Start removing the Send impl for App

Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Nathan <nathan@zed.dev>

crates/ai2/src/providers/open_ai/completion.rs

@@ -4,7 +4,7 @@ use futures::{
     future::BoxFuture, io::BufReader, stream::BoxStream, AsyncBufReadExt, AsyncReadExt, FutureExt,
     Stream, StreamExt,
 };
-use gpui2::{AppContext, Executor};
+use gpui2::{AppContext, BackgroundExecutor};
 use isahc::{http::StatusCode, Request, RequestExt};
 use parking_lot::RwLock;
 use serde::{Deserialize, Serialize};
@@ -105,7 +105,7 @@ pub struct OpenAIResponseStreamEvent {
 
 pub async fn stream_completion(
     credential: ProviderCredential,
-    executor: Arc<Executor>,
+    executor: Arc<BackgroundExecutor>,
     request: Box<dyn CompletionRequest>,
 ) -> Result<impl Stream<Item = Result<OpenAIResponseStreamEvent>>> {
     let api_key = match credential {
@@ -198,11 +198,11 @@ pub async fn stream_completion(
 pub struct OpenAICompletionProvider {
     model: OpenAILanguageModel,
     credential: Arc<RwLock<ProviderCredential>>,
-    executor: Arc<Executor>,
+    executor: Arc<BackgroundExecutor>,
 }
 
 impl OpenAICompletionProvider {
-    pub fn new(model_name: &str, executor: Arc<Executor>) -> Self {
+    pub fn new(model_name: &str, executor: Arc<BackgroundExecutor>) -> Self {
         let model = OpenAILanguageModel::load(model_name);
         let credential = Arc::new(RwLock::new(ProviderCredential::NoCredentials));
         Self {

crates/ai2/src/providers/open_ai/embedding.rs

@@ -1,7 +1,7 @@
 use anyhow::{anyhow, Result};
 use async_trait::async_trait;
 use futures::AsyncReadExt;
-use gpui2::Executor;
+use gpui2::BackgroundExecutor;
 use gpui2::{serde_json, AppContext};
 use isahc::http::StatusCode;
 use isahc::prelude::Configurable;
@@ -35,7 +35,7 @@ pub struct OpenAIEmbeddingProvider {
     model: OpenAILanguageModel,
     credential: Arc<RwLock<ProviderCredential>>,
     pub client: Arc<dyn HttpClient>,
-    pub executor: Arc<Executor>,
+    pub executor: Arc<BackgroundExecutor>,
     rate_limit_count_rx: watch::Receiver<Option<Instant>>,
     rate_limit_count_tx: Arc<Mutex<watch::Sender<Option<Instant>>>>,
 }
@@ -66,7 +66,7 @@ struct OpenAIEmbeddingUsage {
 }
 
 impl OpenAIEmbeddingProvider {
-    pub fn new(client: Arc<dyn HttpClient>, executor: Arc<Executor>) -> Self {
+    pub fn new(client: Arc<dyn HttpClient>, executor: Arc<BackgroundExecutor>) -> Self {
         let (rate_limit_count_tx, rate_limit_count_rx) = watch::channel_with(None);
         let rate_limit_count_tx = Arc::new(Mutex::new(rate_limit_count_tx));
 

crates/audio2/src/audio2.rs

@@ -1,6 +1,6 @@
 use assets::SoundRegistry;
 use futures::{channel::mpsc, StreamExt};
-use gpui2::{AppContext, AssetSource, Executor};
+use gpui2::{AppContext, AssetSource, BackgroundExecutor};
 use rodio::{OutputStream, OutputStreamHandle};
 use util::ResultExt;
 
@@ -34,7 +34,7 @@ impl Sound {
 }
 
 pub struct Audio {
-    tx: mpsc::UnboundedSender<Box<dyn FnOnce(&mut AudioState) + Send>>,
+    tx: mpsc::UnboundedSender<Box<dyn FnOnce(&mut AudioState)>>,
 }
 
 struct AudioState {
@@ -60,8 +60,8 @@ impl AudioState {
 }
 
 impl Audio {
-    pub fn new(executor: &Executor) -> Self {
+    pub fn new(executor: &BackgroundExecutor) -> Self {
-        let (tx, mut rx) = mpsc::unbounded::<Box<dyn FnOnce(&mut AudioState) + Send>>();
+        let (tx, mut rx) = mpsc::unbounded::<Box<dyn FnOnce(&mut AudioState)>>();
         executor
             .spawn_on_main(|| async move {
                 let mut audio = AudioState {

crates/call2/src/room.rs

@@ -445,7 +445,8 @@ impl Room {
 
                 // Wait for client to re-establish a connection to the server.
                 {
-                    let mut reconnection_timeout = cx.executor().timer(RECONNECT_TIMEOUT).fuse();
+                    let mut reconnection_timeout =
+                        cx.background_executor().timer(RECONNECT_TIMEOUT).fuse();
                     let client_reconnection = async {
                         let mut remaining_attempts = 3;
                         while remaining_attempts > 0 {

crates/client2/src/client2.rs

@@ -505,7 +505,7 @@ impl Client {
                                 },
                                 &cx,
                             );
-                            cx.executor().timer(delay).await;
+                            cx.background_executor().timer(delay).await;
                             delay = delay
                                 .mul_f32(rng.gen_range(1.0..=2.0))
                                 .min(reconnect_interval);
@@ -763,7 +763,8 @@ impl Client {
             self.set_status(Status::Reconnecting, cx);
         }
 
-        let mut timeout = futures::FutureExt::fuse(cx.executor().timer(CONNECTION_TIMEOUT));
+        let mut timeout =
+            futures::FutureExt::fuse(cx.background_executor().timer(CONNECTION_TIMEOUT));
         futures::select_biased! {
             connection = self.establish_connection(&credentials, cx).fuse() => {
                 match connection {
@@ -814,7 +815,7 @@ impl Client {
         conn: Connection,
         cx: &AsyncAppContext,
     ) -> Result<()> {
-        let executor = cx.executor();
+        let executor = cx.background_executor();
         log::info!("add connection to peer");
         let (connection_id, handle_io, mut incoming) = self.peer.add_connection(conn, {
             let executor = executor.clone();
@@ -978,7 +979,7 @@ impl Client {
             .header("x-zed-protocol-version", rpc2::PROTOCOL_VERSION);
 
         let http = self.http.clone();
-        cx.executor().spawn(async move {
+        cx.background_executor().spawn(async move {
             let mut rpc_url = Self::get_rpc_url(http, use_preview_server).await?;
             let rpc_host = rpc_url
                 .host_str()
@@ -1382,7 +1383,7 @@ mod tests {
     use super::*;
     use crate::test::FakeServer;
 
-    use gpui2::{Context, Executor, TestAppContext};
+    use gpui2::{BackgroundExecutor, Context, TestAppContext};
     use parking_lot::Mutex;
     use std::future;
     use util::http::FakeHttpClient;
@@ -1422,7 +1423,7 @@ mod tests {
     }
 
     #[gpui2::test(iterations = 10)]
-    async fn test_connection_timeout(executor: Executor, cx: &mut TestAppContext) {
+    async fn test_connection_timeout(executor: BackgroundExecutor, cx: &mut TestAppContext) {
         let user_id = 5;
         let client = cx.update(|cx| Client::new(FakeHttpClient::with_404_response(), cx));
         let mut status = client.status();
@@ -1490,7 +1491,10 @@ mod tests {
     }
 
     #[gpui2::test(iterations = 10)]
-    async fn test_authenticating_more_than_once(cx: &mut TestAppContext, executor: Executor) {
+    async fn test_authenticating_more_than_once(
+        cx: &mut TestAppContext,
+        executor: BackgroundExecutor,
+    ) {
         let auth_count = Arc::new(Mutex::new(0));
         let dropped_auth_count = Arc::new(Mutex::new(0));
         let client = cx.update(|cx| Client::new(FakeHttpClient::with_404_response(), cx));

crates/client2/src/test.rs

@@ -1,7 +1,7 @@
 use crate::{Client, Connection, Credentials, EstablishConnectionError, UserStore};
 use anyhow::{anyhow, Result};
 use futures::{stream::BoxStream, StreamExt};
-use gpui2::{Context, Executor, Model, TestAppContext};
+use gpui2::{BackgroundExecutor, Context, Model, TestAppContext};
 use parking_lot::Mutex;
 use rpc2::{
     proto::{self, GetPrivateUserInfo, GetPrivateUserInfoResponse},
@@ -14,7 +14,7 @@ pub struct FakeServer {
     peer: Arc<Peer>,
     state: Arc<Mutex<FakeServerState>>,
     user_id: u64,
-    executor: Executor,
+    executor: BackgroundExecutor,
 }
 
 #[derive(Default)]
@@ -79,10 +79,10 @@ impl FakeServer {
                         }
 
                         let (client_conn, server_conn, _) =
-                            Connection::in_memory(cx.executor().clone());
+                            Connection::in_memory(cx.background_executor().clone());
                         let (connection_id, io, incoming) =
-                            peer.add_test_connection(server_conn, cx.executor().clone());
+                            peer.add_test_connection(server_conn, cx.background_executor().clone());
-                        cx.executor().spawn(io).detach();
+                        cx.background_executor().spawn(io).detach();
                         {
                             let mut state = state.lock();
                             state.connection_id = Some(connection_id);

crates/copilot2/src/copilot2.rs

@@ -208,7 +208,7 @@ impl RegisteredBuffer {
                 let new_snapshot = buffer.update(&mut cx, |buffer, _| buffer.snapshot()).ok()?;
 
                 let content_changes = cx
-                    .executor()
+                    .background_executor()
                     .spawn({
                         let new_snapshot = new_snapshot.clone();
                         async move {

crates/editor/src/test/editor_lsp_test_context.rs

@@ -266,9 +266,9 @@ impl<'a> EditorLspTestContext<'a> {
     ) -> futures::channel::mpsc::UnboundedReceiver<()>
     where
         T: 'static + request::Request,
-        T::Params: 'static + Send,
+        T::Params: 'static,
-        F: 'static + Send + FnMut(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
+        F: 'static + FnMut(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
-        Fut: 'static + Send + Future<Output = Result<T::Result>>,
+        Fut: 'static + Future<Output = Result<T::Result>>,
     {
         let url = self.buffer_lsp_url.clone();
         self.lsp.handle_request::<T, _, _>(move |params, cx| {

crates/fs2/src/fs2.rs

@@ -288,7 +288,7 @@ impl Fs for RealFs {
 pub struct FakeFs {
     // Use an unfair lock to ensure tests are deterministic.
     state: Mutex<FakeFsState>,
-    executor: gpui2::Executor,
+    executor: gpui2::BackgroundExecutor,
 }
 
 #[cfg(any(test, feature = "test-support"))]
@@ -434,7 +434,7 @@ lazy_static::lazy_static! {
 
 #[cfg(any(test, feature = "test-support"))]
 impl FakeFs {
-    pub fn new(executor: gpui2::Executor) -> Arc<Self> {
+    pub fn new(executor: gpui2::BackgroundExecutor) -> Arc<Self> {
         Arc::new(Self {
             executor,
             state: Mutex::new(FakeFsState {
@@ -1222,11 +1222,11 @@ pub fn copy_recursive<'a>(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use gpui2::Executor;
+    use gpui2::BackgroundExecutor;
     use serde_json::json;
 
     #[gpui2::test]
-    async fn test_fake_fs(executor: Executor) {
+    async fn test_fake_fs(executor: BackgroundExecutor) {
         let fs = FakeFs::new(executor.clone());
         fs.insert_tree(
             "/root",

crates/fuzzy2/src/paths.rs

@@ -1,4 +1,4 @@
-use gpui2::Executor;
+use gpui2::BackgroundExecutor;
 use std::{
     borrow::Cow,
     cmp::{self, Ordering},
@@ -134,7 +134,7 @@ pub async fn match_path_sets<'a, Set: PathMatchCandidateSet<'a>>(
     smart_case: bool,
     max_results: usize,
     cancel_flag: &AtomicBool,
-    executor: Executor,
+    executor: BackgroundExecutor,
 ) -> Vec<PathMatch> {
     let path_count: usize = candidate_sets.iter().map(|s| s.len()).sum();
     if path_count == 0 {

crates/gpui2/src/app.rs

@@ -14,8 +14,8 @@ pub use test_context::*;
 
 use crate::{
     current_platform, image_cache::ImageCache, Action, AnyBox, AnyView, AppMetadata, AssetSource,
-    ClipboardItem, Context, DispatchPhase, DisplayId, Executor, FocusEvent, FocusHandle, FocusId,
+    BackgroundExecutor, ClipboardItem, Context, DispatchPhase, DisplayId, FocusEvent, FocusHandle,
-    KeyBinding, Keymap, LayoutId, MainThread, MainThreadOnly, Pixels, Platform, Point, Render,
+    FocusId, ForegroundExecutor, KeyBinding, Keymap, LayoutId, Pixels, Platform, Point, Render,
     SharedString, SubscriberSet, Subscription, SvgRenderer, Task, TextStyle, TextStyleRefinement,
     TextSystem, View, Window, WindowContext, WindowHandle, WindowId,
 };
@@ -26,17 +26,18 @@ use parking_lot::Mutex;
 use slotmap::SlotMap;
 use std::{
     any::{type_name, Any, TypeId},
-    borrow::Borrow,
+    cell::RefCell,
     marker::PhantomData,
     mem,
     ops::{Deref, DerefMut},
     path::PathBuf,
-    sync::{atomic::Ordering::SeqCst, Arc, Weak},
+    rc::{Rc, Weak},
+    sync::{atomic::Ordering::SeqCst, Arc},
     time::Duration,
 };
 use util::http::{self, HttpClient};
 
-pub struct App(Arc<Mutex<AppContext>>);
+pub struct App(Rc<RefCell<AppContext>>);
 
 /// Represents an application before it is fully launched. Once your app is
 /// configured, you'll start the app with `App::run`.
@@ -54,13 +55,12 @@ impl App {
     /// app is fully launched.
     pub fn run<F>(self, on_finish_launching: F)
     where
-        F: 'static + FnOnce(&mut MainThread<AppContext>),
+        F: 'static + FnOnce(&mut AppContext),
     {
         let this = self.0.clone();
-        let platform = self.0.lock().platform.clone();
+        let platform = self.0.borrow().platform.clone();
-        platform.borrow_on_main_thread().run(Box::new(move || {
+        platform.run(Box::new(move || {
-            let cx = &mut *this.lock();
+            let cx = &mut *this.borrow_mut();
-            let cx = unsafe { mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx) };
             on_finish_launching(cx);
         }));
     }
@@ -71,16 +71,12 @@ impl App {
     where
         F: 'static + FnMut(Vec<String>, &mut AppContext),
     {
-        let this = Arc::downgrade(&self.0);
+        let this = Rc::downgrade(&self.0);
-        self.0
+        self.0.borrow().platform.on_open_urls(Box::new(move |urls| {
-            .lock()
+            if let Some(app) = this.upgrade() {
-            .platform
+                callback(urls, &mut *app.borrow_mut());
-            .borrow_on_main_thread()
+            }
-            .on_open_urls(Box::new(move |urls| {
+        }));
-                if let Some(app) = this.upgrade() {
-                    callback(urls, &mut app.lock());
-                }
-            }));
         self
     }
 
@@ -88,29 +84,25 @@ impl App {
     where
         F: 'static + FnMut(&mut AppContext),
     {
-        let this = Arc::downgrade(&self.0);
+        let this = Rc::downgrade(&self.0);
-        self.0
+        self.0.borrow_mut().platform.on_reopen(Box::new(move || {
-            .lock()
+            if let Some(app) = this.upgrade() {
-            .platform
+                callback(&mut app.borrow_mut());
-            .borrow_on_main_thread()
+            }
-            .on_reopen(Box::new(move || {
+        }));
-                if let Some(app) = this.upgrade() {
-                    callback(&mut app.lock());
-                }
-            }));
         self
     }
 
     pub fn metadata(&self) -> AppMetadata {
-        self.0.lock().app_metadata.clone()
+        self.0.borrow().app_metadata.clone()
     }
 
-    pub fn executor(&self) -> Executor {
+    pub fn background_executor(&self) -> BackgroundExecutor {
-        self.0.lock().executor.clone()
+        self.0.borrow().background_executor.clone()
     }
 
     pub fn text_system(&self) -> Arc<TextSystem> {
-        self.0.lock().text_system.clone()
+        self.0.borrow().text_system.clone()
     }
 }
 
@@ -122,15 +114,16 @@ type QuitHandler = Box<dyn FnMut(&mut AppContext) -> BoxFuture<'static, ()> + Se
 type ReleaseListener = Box<dyn FnMut(&mut dyn Any, &mut AppContext) + Send + 'static>;
 
 pub struct AppContext {
-    this: Weak<Mutex<AppContext>>,
+    this: Weak<RefCell<AppContext>>,
-    pub(crate) platform: MainThreadOnly<dyn Platform>,
+    pub(crate) platform: Rc<dyn Platform>,
     app_metadata: AppMetadata,
     text_system: Arc<TextSystem>,
     flushing_effects: bool,
     pending_updates: usize,
     pub(crate) active_drag: Option<AnyDrag>,
     pub(crate) next_frame_callbacks: HashMap<DisplayId, Vec<FrameCallback>>,
-    pub(crate) executor: Executor,
+    pub(crate) background_executor: BackgroundExecutor,
+    pub(crate) foreground_executor: ForegroundExecutor,
     pub(crate) svg_renderer: SvgRenderer,
     asset_source: Arc<dyn AssetSource>,
     pub(crate) image_cache: ImageCache,
@@ -156,11 +149,12 @@ pub struct AppContext {
 
 impl AppContext {
     pub(crate) fn new(
-        platform: Arc<dyn Platform>,
+        platform: Rc<dyn Platform>,
         asset_source: Arc<dyn AssetSource>,
         http_client: Arc<dyn HttpClient>,
-    ) -> Arc<Mutex<Self>> {
+    ) -> Rc<RefCell<Self>> {
-        let executor = platform.executor();
+        let executor = platform.background_executor();
+        let foreground_executor = platform.foreground_executor();
         assert!(
             executor.is_main_thread(),
             "must construct App on main thread"
@@ -175,16 +169,17 @@ impl AppContext {
             app_version: platform.app_version().ok(),
         };
 
-        Arc::new_cyclic(|this| {
+        Rc::new_cyclic(|this| {
-            Mutex::new(AppContext {
+            RefCell::new(AppContext {
                 this: this.clone(),
                 text_system,
-                platform: MainThreadOnly::new(platform, executor.clone()),
+                platform,
                 app_metadata,
                 flushing_effects: false,
                 pending_updates: 0,
                 next_frame_callbacks: Default::default(),
-                executor,
+                background_executor: executor,
+                foreground_executor,
                 svg_renderer: SvgRenderer::new(asset_source.clone()),
                 asset_source,
                 image_cache: ImageCache::new(http_client),
@@ -225,7 +220,7 @@ impl AppContext {
 
         let futures = futures::future::join_all(futures);
         if self
-            .executor
+            .background_executor
             .block_with_timeout(Duration::from_millis(100), futures)
             .is_err()
         {
@@ -244,7 +239,6 @@ impl AppContext {
     pub fn refresh(&mut self) {
         self.pending_effects.push_back(Effect::Refresh);
     }
-
     pub(crate) fn update<R>(&mut self, update: impl FnOnce(&mut Self) -> R) -> R {
         self.pending_updates += 1;
         let result = update(self);
@@ -258,7 +252,7 @@ impl AppContext {
     }
 
     pub(crate) fn read_window<R>(
-        &mut self,
+        &self,
         id: WindowId,
         read: impl FnOnce(&WindowContext) -> R,
     ) -> Result<R> {
@@ -295,6 +289,68 @@ impl AppContext {
         })
     }
 
+    /// Opens a new window with the given option and the root view returned by the given function.
+    /// The function is invoked with a `WindowContext`, which can be used to interact with window-specific
+    /// functionality.
+    pub fn open_window<V: Render>(
+        &mut self,
+        options: crate::WindowOptions,
+        build_root_view: impl FnOnce(&mut WindowContext) -> View<V> + Send + 'static,
+    ) -> WindowHandle<V> {
+        self.update(|cx| {
+            let id = cx.windows.insert(None);
+            let handle = WindowHandle::new(id);
+            let mut window = Window::new(handle.into(), options, cx);
+            let root_view = build_root_view(&mut WindowContext::mutable(cx, &mut window));
+            window.root_view.replace(root_view.into());
+            cx.windows.get_mut(id).unwrap().replace(window);
+            handle
+        })
+    }
+
+    pub(crate) fn platform(&self) -> &Rc<dyn Platform> {
+        &self.platform
+    }
+
+    /// Instructs the platform to activate the application by bringing it to the foreground.
+    pub fn activate(&self, ignoring_other_apps: bool) {
+        self.platform().activate(ignoring_other_apps);
+    }
+
+    /// Writes data to the platform clipboard.
+    pub fn write_to_clipboard(&self, item: ClipboardItem) {
+        self.platform().write_to_clipboard(item)
+    }
+
+    /// Reads data from the platform clipboard.
+    pub fn read_from_clipboard(&self) -> Option<ClipboardItem> {
+        self.platform().read_from_clipboard()
+    }
+
+    /// Writes credentials to the platform keychain.
+    pub fn write_credentials(&self, url: &str, username: &str, password: &[u8]) -> Result<()> {
+        self.platform().write_credentials(url, username, password)
+    }
+
+    /// Reads credentials from the platform keychain.
+    pub fn read_credentials(&self, url: &str) -> Result<Option<(String, Vec<u8>)>> {
+        self.platform().read_credentials(url)
+    }
+
+    /// Deletes credentials from the platform keychain.
+    pub fn delete_credentials(&self, url: &str) -> Result<()> {
+        self.platform().delete_credentials(url)
+    }
+
+    /// Directs the platform's default browser to open the given URL.
+    pub fn open_url(&self, url: &str) {
+        self.platform().open_url(url);
+    }
+
+    pub fn path_for_auxiliary_executable(&self, name: &str) -> Result<PathBuf> {
+        self.platform().path_for_auxiliary_executable(name)
+    }
+
     pub(crate) fn push_effect(&mut self, effect: Effect) {
         match &effect {
             Effect::Notify { emitter } => {
@@ -473,67 +529,24 @@ impl AppContext {
     pub fn to_async(&self) -> AsyncAppContext {
         AsyncAppContext {
             app: unsafe { mem::transmute(self.this.clone()) },
-            executor: self.executor.clone(),
+            background_executor: self.background_executor.clone(),
+            foreground_executor: self.foreground_executor.clone(),
         }
     }
 
     /// Obtains a reference to the executor, which can be used to spawn futures.
-    pub fn executor(&self) -> &Executor {
+    pub fn executor(&self) -> &BackgroundExecutor {
-        &self.executor
+        &self.background_executor
-    }
-
-    /// Runs the given closure on the main thread, where interaction with the platform
-    /// is possible. The given closure will be invoked with a `MainThread<AppContext>`, which
-    /// has platform-specific methods that aren't present on `AppContext`.
-    pub fn run_on_main<R>(
-        &mut self,
-        f: impl FnOnce(&mut MainThread<AppContext>) -> R + Send + 'static,
-    ) -> Task<R>
-    where
-        R: Send + 'static,
-    {
-        if self.executor.is_main_thread() {
-            Task::ready(f(unsafe {
-                mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(self)
-            }))
-        } else {
-            let this = self.this.upgrade().unwrap();
-            self.executor.run_on_main(move || {
-                let cx = &mut *this.lock();
-                cx.update(|cx| f(unsafe { mem::transmute::<&mut Self, &mut MainThread<Self>>(cx) }))
-            })
-        }
-    }
-
-    /// Spawns the future returned by the given function on the main thread, where interaction with
-    /// the platform is possible. The given closure will be invoked with a `MainThread<AsyncAppContext>`,
-    /// which has platform-specific methods that aren't present on `AsyncAppContext`. The future will be
-    /// polled exclusively on the main thread.
-    // todo!("I think we need somehow to prevent the MainThread<AsyncAppContext> from implementing Send")
-    pub fn spawn_on_main<F, R>(
-        &self,
-        f: impl FnOnce(MainThread<AsyncAppContext>) -> F + Send + 'static,
-    ) -> Task<R>
-    where
-        F: Future<Output = R> + 'static,
-        R: Send + 'static,
-    {
-        let cx = self.to_async();
-        self.executor.spawn_on_main(move || f(MainThread(cx)))
     }
 
     /// Spawns the future returned by the given function on the thread pool. The closure will be invoked
     /// with AsyncAppContext, which allows the application state to be accessed across await points.
-    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut + Send + 'static) -> Task<R>
+    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut) -> Task<R>
     where
-        Fut: Future<Output = R> + Send + 'static,
+        Fut: Future<Output = R> + 'static,
-        R: Send + 'static,
+        R: 'static,
     {
-        let cx = self.to_async();
+        self.foreground_executor.spawn(f(self.to_async()))
-        self.executor.spawn(async move {
-            let future = f(cx);
-            future.await
-        })
     }
 
     /// Schedules the given function to be run at the end of the current effect cycle, allowing entities
@@ -597,7 +610,7 @@ impl AppContext {
 
     /// Access the global of the given type mutably. A default value is assigned if a global of this type has not
     /// yet been assigned.
-    pub fn default_global<G: 'static + Default + Send>(&mut self) -> &mut G {
+    pub fn default_global<G: 'static + Default>(&mut self) -> &mut G {
         let global_type = TypeId::of::<G>();
         self.push_effect(Effect::NotifyGlobalObservers { global_type });
         self.globals_by_type
@@ -608,7 +621,7 @@ impl AppContext {
     }
 
     /// Set the value of the global of the given type.
-    pub fn set_global<G: Any + Send>(&mut self, global: G) {
+    pub fn set_global<G: Any>(&mut self, global: G) {
         let global_type = TypeId::of::<G>();
         self.push_effect(Effect::NotifyGlobalObservers { global_type });
         self.globals_by_type.insert(global_type, Box::new(global));
@@ -717,7 +730,7 @@ impl Context for AppContext {
     /// Build an entity that is owned by the application. The given function will be invoked with
     /// a `ModelContext` and must return an object representing the entity. A `Model` will be returned
     /// which can be used to access the entity in a context.
-    fn build_model<T: 'static + Send>(
+    fn build_model<T: 'static>(
         &mut self,
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
     ) -> Model<T> {
@@ -747,107 +760,6 @@ impl Context for AppContext {
     }
 }
 
-impl<C> MainThread<C>
-where
-    C: Borrow<AppContext>,
-{
-    pub(crate) fn platform(&self) -> &dyn Platform {
-        self.0.borrow().platform.borrow_on_main_thread()
-    }
-
-    /// Instructs the platform to activate the application by bringing it to the foreground.
-    pub fn activate(&self, ignoring_other_apps: bool) {
-        self.platform().activate(ignoring_other_apps);
-    }
-
-    /// Writes data to the platform clipboard.
-    pub fn write_to_clipboard(&self, item: ClipboardItem) {
-        self.platform().write_to_clipboard(item)
-    }
-
-    /// Reads data from the platform clipboard.
-    pub fn read_from_clipboard(&self) -> Option<ClipboardItem> {
-        self.platform().read_from_clipboard()
-    }
-
-    /// Writes credentials to the platform keychain.
-    pub fn write_credentials(&self, url: &str, username: &str, password: &[u8]) -> Result<()> {
-        self.platform().write_credentials(url, username, password)
-    }
-
-    /// Reads credentials from the platform keychain.
-    pub fn read_credentials(&self, url: &str) -> Result<Option<(String, Vec<u8>)>> {
-        self.platform().read_credentials(url)
-    }
-
-    /// Deletes credentials from the platform keychain.
-    pub fn delete_credentials(&self, url: &str) -> Result<()> {
-        self.platform().delete_credentials(url)
-    }
-
-    /// Directs the platform's default browser to open the given URL.
-    pub fn open_url(&self, url: &str) {
-        self.platform().open_url(url);
-    }
-
-    pub fn path_for_auxiliary_executable(&self, name: &str) -> Result<PathBuf> {
-        self.platform().path_for_auxiliary_executable(name)
-    }
-}
-
-impl MainThread<AppContext> {
-    fn update<R>(&mut self, update: impl FnOnce(&mut Self) -> R) -> R {
-        self.0.update(|cx| {
-            update(unsafe {
-                std::mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx)
-            })
-        })
-    }
-
-    pub(crate) fn update_window<R>(
-        &mut self,
-        id: WindowId,
-        update: impl FnOnce(&mut MainThread<WindowContext>) -> R,
-    ) -> Result<R> {
-        self.0.update_window(id, |cx| {
-            update(unsafe {
-                std::mem::transmute::<&mut WindowContext, &mut MainThread<WindowContext>>(cx)
-            })
-        })
-    }
-
-    /// Opens a new window with the given option and the root view returned by the given function.
-    /// The function is invoked with a `WindowContext`, which can be used to interact with window-specific
-    /// functionality.
-    pub fn open_window<V: Render>(
-        &mut self,
-        options: crate::WindowOptions,
-        build_root_view: impl FnOnce(&mut WindowContext) -> View<V> + Send + 'static,
-    ) -> WindowHandle<V> {
-        self.update(|cx| {
-            let id = cx.windows.insert(None);
-            let handle = WindowHandle::new(id);
-            let mut window = Window::new(handle.into(), options, cx);
-            let root_view = build_root_view(&mut WindowContext::mutable(cx, &mut window));
-            window.root_view.replace(root_view.into());
-            cx.windows.get_mut(id).unwrap().replace(window);
-            handle
-        })
-    }
-
-    /// Update the global of the given type with a closure. Unlike `global_mut`, this method provides
-    /// your closure with mutable access to the `MainThread<AppContext>` and the global simultaneously.
-    pub fn update_global<G: 'static + Send, R>(
-        &mut self,
-        update: impl FnOnce(&mut G, &mut MainThread<AppContext>) -> R,
-    ) -> R {
-        self.0.update_global(|global, cx| {
-            let cx = unsafe { mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx) };
-            update(global, cx)
-        })
-    }
-}
-
 /// These effects are processed at the end of each application update cycle.
 pub(crate) enum Effect {
     Notify {
@@ -855,7 +767,7 @@ pub(crate) enum Effect {
     },
     Emit {
         emitter: EntityId,
-        event: Box<dyn Any + Send + 'static>,
+        event: Box<dyn Any>,
     },
     FocusChanged {
         window_id: WindowId,
@@ -905,15 +817,3 @@ pub(crate) struct AnyDrag {
     pub view: AnyView,
     pub cursor_offset: Point<Pixels>,
 }
-
-#[cfg(test)]
-mod tests {
-    use super::AppContext;
-
-    #[test]
-    fn test_app_context_send_sync() {
-        // This will not compile if `AppContext` does not implement `Send`
-        fn assert_send<T: Send>() {}
-        assert_send::<AppContext>();
-    }
-}

crates/gpui2/src/app/async_context.rs

@@ -1,16 +1,16 @@
 use crate::{
-    AnyWindowHandle, AppContext, Context, Executor, MainThread, Model, ModelContext, Result, Task,
+    AnyWindowHandle, AppContext, BackgroundExecutor, Context, ForegroundExecutor, Model,
-    WindowContext,
+    ModelContext, Result, Task, WindowContext,
 };
 use anyhow::anyhow;
 use derive_more::{Deref, DerefMut};
-use parking_lot::Mutex;
+use std::{cell::RefCell, future::Future, rc::Weak};
-use std::{future::Future, sync::Weak};
 
 #[derive(Clone)]
 pub struct AsyncAppContext {
-    pub(crate) app: Weak<Mutex<AppContext>>,
+    pub(crate) app: Weak<RefCell<AppContext>>,
-    pub(crate) executor: Executor,
+    pub(crate) background_executor: BackgroundExecutor,
+    pub(crate) foreground_executor: ForegroundExecutor,
 }
 
 impl Context for AsyncAppContext {
@@ -22,14 +22,14 @@ impl Context for AsyncAppContext {
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
     ) -> Self::Result<Model<T>>
     where
-        T: 'static + Send,
+        T: 'static,
     {
         let app = self
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut lock = app.lock(); // Need this to compile
+        let mut app = app.borrow_mut();
-        Ok(lock.build_model(build_model))
+        Ok(app.build_model(build_model))
     }
 
     fn update_model<T: 'static, R>(
@@ -41,8 +41,8 @@ impl Context for AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut lock = app.lock(); // Need this to compile
+        let mut app = app.borrow_mut();
-        Ok(lock.update_model(handle, update))
+        Ok(app.update_model(handle, update))
     }
 }
 
@@ -52,13 +52,17 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut lock = app.lock(); // Need this to compile
+        let mut lock = app.borrow_mut();
         lock.refresh();
         Ok(())
     }
 
-    pub fn executor(&self) -> &Executor {
+    pub fn background_executor(&self) -> &BackgroundExecutor {
-        &self.executor
+        &self.background_executor
+    }
+
+    pub fn foreground_executor(&self) -> &ForegroundExecutor {
+        &self.foreground_executor
     }
 
     pub fn update<R>(&self, f: impl FnOnce(&mut AppContext) -> R) -> Result<R> {
@@ -66,7 +70,7 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut lock = app.lock();
+        let mut lock = app.borrow_mut();
         Ok(f(&mut *lock))
     }
 
@@ -79,7 +83,7 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut app_context = app.lock();
+        let app_context = app.borrow();
         app_context.read_window(handle.id, update)
     }
 
@@ -92,44 +96,16 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut app_context = app.lock();
+        let mut app_context = app.borrow_mut();
         app_context.update_window(handle.id, update)
     }
 
-    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut + Send + 'static) -> Task<R>
+    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut) -> Task<R>
-    where
-        Fut: Future<Output = R> + Send + 'static,
-        R: Send + 'static,
-    {
-        let this = self.clone();
-        self.executor.spawn(async move { f(this).await })
-    }
-
-    pub fn spawn_on_main<Fut, R>(
-        &self,
-        f: impl FnOnce(AsyncAppContext) -> Fut + Send + 'static,
-    ) -> Task<R>
     where
         Fut: Future<Output = R> + 'static,
-        R: Send + 'static,
+        R: 'static,
     {
-        let this = self.clone();
+        self.foreground_executor.spawn(f(self.clone()))
-        self.executor.spawn_on_main(|| f(this))
-    }
-
-    pub fn run_on_main<R>(
-        &self,
-        f: impl FnOnce(&mut MainThread<AppContext>) -> R + Send + 'static,
-    ) -> Result<Task<R>>
-    where
-        R: Send + 'static,
-    {
-        let app = self
-            .app
-            .upgrade()
-            .ok_or_else(|| anyhow!("app was released"))?;
-        let mut app_context = app.lock();
-        Ok(app_context.run_on_main(f))
     }
 
     pub fn has_global<G: 'static>(&self) -> Result<bool> {
@@ -137,8 +113,8 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let lock = app.lock(); // Need this to compile
+        let app = app.borrow_mut();
-        Ok(lock.has_global::<G>())
+        Ok(app.has_global::<G>())
     }
 
     pub fn read_global<G: 'static, R>(&self, read: impl FnOnce(&G, &AppContext) -> R) -> Result<R> {
@@ -146,8 +122,8 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let lock = app.lock(); // Need this to compile
+        let app = app.borrow_mut(); // Need this to compile
-        Ok(read(lock.global(), &lock))
+        Ok(read(app.global(), &app))
     }
 
     pub fn try_read_global<G: 'static, R>(
@@ -155,8 +131,8 @@ impl AsyncAppContext {
         read: impl FnOnce(&G, &AppContext) -> R,
     ) -> Option<R> {
         let app = self.app.upgrade()?;
-        let lock = app.lock(); // Need this to compile
+        let app = app.borrow_mut();
-        Some(read(lock.try_global()?, &lock))
+        Some(read(app.try_global()?, &app))
     }
 
     pub fn update_global<G: 'static, R>(
@@ -167,8 +143,8 @@ impl AsyncAppContext {
             .app
             .upgrade()
             .ok_or_else(|| anyhow!("app was released"))?;
-        let mut lock = app.lock(); // Need this to compile
+        let mut app = app.borrow_mut();
-        Ok(lock.update_global(update))
+        Ok(app.update_global(update))
     }
 }
 
@@ -224,7 +200,7 @@ impl Context for AsyncWindowContext {
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
     ) -> Result<Model<T>>
     where
-        T: 'static + Send,
+        T: 'static,
     {
         self.app
             .update_window(self.window, |cx| cx.build_model(build_model))
@@ -239,14 +215,3 @@ impl Context for AsyncWindowContext {
             .update_window(self.window, |cx| cx.update_model(handle, update))
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_async_app_context_send_sync() {
-        fn assert_send_sync<T: Send + Sync>() {}
-        assert_send_sync::<AsyncAppContext>();
-    }
-}

crates/gpui2/src/app/entity_map.rs

@@ -59,7 +59,7 @@ impl EntityMap {
     /// Insert an entity into a slot obtained by calling `reserve`.
     pub fn insert<T>(&mut self, slot: Slot<T>, entity: T) -> Model<T>
     where
-        T: 'static + Send,
+        T: 'static,
     {
         let model = slot.0;
         self.entities.insert(model.entity_id, Box::new(entity));

crates/gpui2/src/app/model_context.rs

@@ -1,6 +1,6 @@
 use crate::{
-    AppContext, AsyncAppContext, Context, Effect, Entity, EntityId, EventEmitter, MainThread,
+    AppContext, AsyncAppContext, Context, Effect, Entity, EntityId, EventEmitter, Model, Reference,
-    Model, Reference, Subscription, Task, WeakModel,
+    Subscription, Task, WeakModel,
 };
 use derive_more::{Deref, DerefMut};
 use futures::FutureExt;
@@ -191,36 +191,20 @@ impl<'a, T: 'static> ModelContext<'a, T> {
         result
     }
 
-    pub fn spawn<Fut, R>(
+    pub fn spawn<Fut, R>(&self, f: impl FnOnce(WeakModel<T>, AsyncAppContext) -> Fut) -> Task<R>
-        &self,
-        f: impl FnOnce(WeakModel<T>, AsyncAppContext) -> Fut + Send + 'static,
-    ) -> Task<R>
     where
         T: 'static,
-        Fut: Future<Output = R> + Send + 'static,
+        Fut: Future<Output = R> + 'static,
-        R: Send + 'static,
+        R: 'static,
     {
         let this = self.weak_model();
         self.app.spawn(|cx| f(this, cx))
     }
-
-    pub fn spawn_on_main<Fut, R>(
-        &self,
-        f: impl FnOnce(WeakModel<T>, MainThread<AsyncAppContext>) -> Fut + Send + 'static,
-    ) -> Task<R>
-    where
-        Fut: Future<Output = R> + 'static,
-        R: Send + 'static,
-    {
-        let this = self.weak_model();
-        self.app.spawn_on_main(|cx| f(this, cx))
-    }
 }
 
 impl<'a, T> ModelContext<'a, T>
 where
     T: EventEmitter,
-    T::Event: Send,
 {
     pub fn emit(&mut self, event: T::Event) {
         self.app.pending_effects.push_back(Effect::Emit {
@@ -234,13 +218,10 @@ impl<'a, T> Context for ModelContext<'a, T> {
     type ModelContext<'b, U> = ModelContext<'b, U>;
     type Result<U> = U;
 
-    fn build_model<U>(
+    fn build_model<U: 'static>(
         &mut self,
         build_model: impl FnOnce(&mut Self::ModelContext<'_, U>) -> U,
-    ) -> Model<U>
+    ) -> Model<U> {
-    where
-        U: 'static + Send,
-    {
         self.app.build_model(build_model)
     }
 

crates/gpui2/src/app/test_context.rs

@@ -1,15 +1,16 @@
 use crate::{
-    AnyWindowHandle, AppContext, AsyncAppContext, Context, EventEmitter, Executor, MainThread,
+    AnyWindowHandle, AppContext, AsyncAppContext, BackgroundExecutor, Context, EventEmitter,
-    Model, ModelContext, Result, Task, TestDispatcher, TestPlatform, WindowContext,
+    ForegroundExecutor, Model, ModelContext, Result, Task, TestDispatcher, TestPlatform,
+    WindowContext,
 };
 use futures::SinkExt;
-use parking_lot::Mutex;
+use std::{cell::RefCell, future::Future, rc::Rc, sync::Arc};
-use std::{future::Future, sync::Arc};
 
 #[derive(Clone)]
 pub struct TestAppContext {
-    pub app: Arc<Mutex<AppContext>>,
+    pub app: Rc<RefCell<AppContext>>,
-    pub executor: Executor,
+    pub background_executor: BackgroundExecutor,
+    pub foreground_executor: ForegroundExecutor,
 }
 
 impl Context for TestAppContext {
@@ -21,10 +22,10 @@ impl Context for TestAppContext {
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
     ) -> Self::Result<Model<T>>
     where
-        T: 'static + Send,
+        T: 'static,
     {
-        let mut lock = self.app.lock();
+        let mut app = self.app.borrow_mut();
-        lock.build_model(build_model)
+        app.build_model(build_model)
     }
 
     fn update_model<T: 'static, R>(
@@ -32,39 +33,45 @@ impl Context for TestAppContext {
         handle: &Model<T>,
         update: impl FnOnce(&mut T, &mut Self::ModelContext<'_, T>) -> R,
     ) -> Self::Result<R> {
-        let mut lock = self.app.lock();
+        let mut app = self.app.borrow_mut();
-        lock.update_model(handle, update)
+        app.update_model(handle, update)
     }
 }
 
 impl TestAppContext {
     pub fn new(dispatcher: TestDispatcher) -> Self {
-        let executor = Executor::new(Arc::new(dispatcher));
+        let dispatcher = Arc::new(dispatcher);
-        let platform = Arc::new(TestPlatform::new(executor.clone()));
+        let background_executor = BackgroundExecutor::new(dispatcher.clone());
+        let foreground_executor = ForegroundExecutor::new(dispatcher);
+        let platform = Rc::new(TestPlatform::new(
+            background_executor.clone(),
+            foreground_executor.clone(),
+        ));
         let asset_source = Arc::new(());
         let http_client = util::http::FakeHttpClient::with_404_response();
         Self {
             app: AppContext::new(platform, asset_source, http_client),
-            executor,
+            background_executor,
+            foreground_executor,
         }
     }
 
     pub fn quit(&self) {
-        self.app.lock().quit();
+        self.app.borrow_mut().quit();
     }
 
     pub fn refresh(&mut self) -> Result<()> {
-        let mut lock = self.app.lock();
+        let mut app = self.app.borrow_mut();
-        lock.refresh();
+        app.refresh();
         Ok(())
     }
 
-    pub fn executor(&self) -> &Executor {
+    pub fn executor(&self) -> &BackgroundExecutor {
-        &self.executor
+        &self.background_executor
     }
 
     pub fn update<R>(&self, f: impl FnOnce(&mut AppContext) -> R) -> R {
-        let mut cx = self.app.lock();
+        let mut cx = self.app.borrow_mut();
         cx.update(f)
     }
 
@@ -73,7 +80,7 @@ impl TestAppContext {
         handle: AnyWindowHandle,
         read: impl FnOnce(&WindowContext) -> R,
     ) -> R {
-        let mut app_context = self.app.lock();
+        let app_context = self.app.borrow();
         app_context.read_window(handle.id, read).unwrap()
     }
 
@@ -82,57 +89,33 @@ impl TestAppContext {
         handle: AnyWindowHandle,
         update: impl FnOnce(&mut WindowContext) -> R,
     ) -> R {
-        let mut app = self.app.lock();
+        let mut app = self.app.borrow_mut();
         app.update_window(handle.id, update).unwrap()
     }
 
-    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut + Send + 'static) -> Task<R>
+    pub fn spawn<Fut, R>(&self, f: impl FnOnce(AsyncAppContext) -> Fut) -> Task<R>
-    where
-        Fut: Future<Output = R> + Send + 'static,
-        R: Send + 'static,
-    {
-        let cx = self.to_async();
-        self.executor.spawn(async move { f(cx).await })
-    }
-
-    pub fn spawn_on_main<Fut, R>(
-        &self,
-        f: impl FnOnce(AsyncAppContext) -> Fut + Send + 'static,
-    ) -> Task<R>
     where
         Fut: Future<Output = R> + 'static,
-        R: Send + 'static,
+        R: 'static,
     {
-        let cx = self.to_async();
+        self.foreground_executor.spawn(f(self.to_async()))
-        self.executor.spawn_on_main(|| f(cx))
-    }
-
-    pub fn run_on_main<R>(
-        &self,
-        f: impl FnOnce(&mut MainThread<AppContext>) -> R + Send + 'static,
-    ) -> Task<R>
-    where
-        R: Send + 'static,
-    {
-        let mut app_context = self.app.lock();
-        app_context.run_on_main(f)
     }
 
     pub fn has_global<G: 'static>(&self) -> bool {
-        let lock = self.app.lock();
+        let app = self.app.borrow();
-        lock.has_global::<G>()
+        app.has_global::<G>()
     }
 
     pub fn read_global<G: 'static, R>(&self, read: impl FnOnce(&G, &AppContext) -> R) -> R {
-        let lock = self.app.lock();
+        let app = self.app.borrow();
-        read(lock.global(), &lock)
+        read(app.global(), &app)
     }
 
     pub fn try_read_global<G: 'static, R>(
         &self,
         read: impl FnOnce(&G, &AppContext) -> R,
     ) -> Option<R> {
-        let lock = self.app.lock();
+        let lock = self.app.borrow();
         Some(read(lock.try_global()?, &lock))
     }
 
@@ -140,14 +123,15 @@ impl TestAppContext {
         &mut self,
         update: impl FnOnce(&mut G, &mut AppContext) -> R,
     ) -> R {
-        let mut lock = self.app.lock();
+        let mut lock = self.app.borrow_mut();
         lock.update_global(update)
     }
 
     pub fn to_async(&self) -> AsyncAppContext {
         AsyncAppContext {
-            app: Arc::downgrade(&self.app),
+            app: Rc::downgrade(&self.app),
-            executor: self.executor.clone(),
+            background_executor: self.background_executor.clone(),
+            foreground_executor: self.foreground_executor.clone(),
         }
     }
 

crates/gpui2/src/assets.rs

@@ -8,7 +8,7 @@ use std::{
     sync::atomic::{AtomicUsize, Ordering::SeqCst},
 };
 
-pub trait AssetSource: 'static + Send + Sync {
+pub trait AssetSource: 'static + Sync {
     fn load(&self, path: &str) -> Result<Cow<[u8]>>;
     fn list(&self, path: &str) -> Result<Vec<SharedString>>;
 }

crates/gpui2/src/element.rs

@@ -4,7 +4,7 @@ pub(crate) use smallvec::SmallVec;
 use std::{any::Any, mem};
 
 pub trait Element<V: 'static> {
-    type ElementState: 'static + Send;
+    type ElementState: 'static;
 
     fn id(&self) -> Option<ElementId>;
 
@@ -97,7 +97,7 @@ impl<V, E: Element<V>> RenderedElement<V, E> {
 impl<V, E> ElementObject<V> for RenderedElement<V, E>
 where
     E: Element<V>,
-    E::ElementState: 'static + Send,
+    E::ElementState: 'static,
 {
     fn initialize(&mut self, view_state: &mut V, cx: &mut ViewContext<V>) {
         let frame_state = if let Some(id) = self.element.id() {
@@ -170,16 +170,14 @@ where
     }
 }
 
-pub struct AnyElement<V>(Box<dyn ElementObject<V> + Send>);
+pub struct AnyElement<V>(Box<dyn ElementObject<V>>);
-
-unsafe impl<V> Send for AnyElement<V> {}
 
 impl<V> AnyElement<V> {
     pub fn new<E>(element: E) -> Self
     where
         V: 'static,
-        E: 'static + Element<V> + Send,
+        E: 'static + Element<V>,
-        E::ElementState: Any + Send,
+        E::ElementState: Any,
     {
         AnyElement(Box::new(RenderedElement::new(element)))
     }

crates/gpui2/src/executor.rs

@@ -6,6 +6,7 @@ use std::{
     marker::PhantomData,
     mem,
     pin::Pin,
+    rc::Rc,
     sync::{
         atomic::{AtomicBool, Ordering::SeqCst},
         Arc,
@@ -17,10 +18,16 @@ use util::TryFutureExt;
 use waker_fn::waker_fn;
 
 #[derive(Clone)]
-pub struct Executor {
+pub struct BackgroundExecutor {
     dispatcher: Arc<dyn PlatformDispatcher>,
 }
 
+#[derive(Clone)]
+pub struct ForegroundExecutor {
+    dispatcher: Arc<dyn PlatformDispatcher>,
+    not_send: PhantomData<Rc<()>>,
+}
+
 #[must_use]
 pub enum Task<T> {
     Ready(Option<T>),
@@ -61,7 +68,7 @@ impl<T> Future for Task<T> {
     }
 }
 
-impl Executor {
+impl BackgroundExecutor {
     pub fn new(dispatcher: Arc<dyn PlatformDispatcher>) -> Self {
         Self { dispatcher }
     }
@@ -79,63 +86,6 @@ impl Executor {
         Task::Spawned(task)
     }
 
-    /// Enqueues the given closure to run on the application's event loop.
-    /// Returns the result asynchronously.
-    pub fn run_on_main<F, R>(&self, func: F) -> Task<R>
-    where
-        F: FnOnce() -> R + Send + 'static,
-        R: Send + 'static,
-    {
-        if self.dispatcher.is_main_thread() {
-            Task::ready(func())
-        } else {
-            self.spawn_on_main(move || async move { func() })
-        }
-    }
-
-    /// Enqueues the given closure to be run on the application's event loop. The
-    /// closure returns a future which will be run to completion on the main thread.
-    pub fn spawn_on_main<F, R>(&self, func: impl FnOnce() -> F + Send + 'static) -> Task<R>
-    where
-        F: Future<Output = R> + 'static,
-        R: Send + 'static,
-    {
-        let (runnable, task) = async_task::spawn(
-            {
-                let this = self.clone();
-                async move {
-                    let task = this.spawn_on_main_local(func());
-                    task.await
-                }
-            },
-            {
-                let dispatcher = self.dispatcher.clone();
-                move |runnable| dispatcher.dispatch_on_main_thread(runnable)
-            },
-        );
-        runnable.schedule();
-        Task::Spawned(task)
-    }
-
-    /// Enqueues the given closure to be run on the application's event loop. Must
-    /// be called on the main thread.
-    pub fn spawn_on_main_local<R>(&self, future: impl Future<Output = R> + 'static) -> Task<R>
-    where
-        R: 'static,
-    {
-        assert!(
-            self.dispatcher.is_main_thread(),
-            "must be called on main thread"
-        );
-
-        let dispatcher = self.dispatcher.clone();
-        let (runnable, task) = async_task::spawn_local(future, move |runnable| {
-            dispatcher.dispatch_on_main_thread(runnable)
-        });
-        runnable.schedule();
-        Task::Spawned(task)
-    }
-
     pub fn block<R>(&self, future: impl Future<Output = R>) -> R {
         pin_mut!(future);
         let (parker, unparker) = parking::pair();
@@ -261,8 +211,31 @@ impl Executor {
     }
 }
 
+impl ForegroundExecutor {
+    pub fn new(dispatcher: Arc<dyn PlatformDispatcher>) -> Self {
+        Self {
+            dispatcher,
+            not_send: PhantomData,
+        }
+    }
+
+    /// Enqueues the given closure to be run on any thread. The closure returns
+    /// a future which will be run to completion on any available thread.
+    pub fn spawn<R>(&self, future: impl Future<Output = R> + 'static) -> Task<R>
+    where
+        R: 'static,
+    {
+        let dispatcher = self.dispatcher.clone();
+        let (runnable, task) = async_task::spawn_local(future, move |runnable| {
+            dispatcher.dispatch_on_main_thread(runnable)
+        });
+        runnable.schedule();
+        Task::Spawned(task)
+    }
+}
+
 pub struct Scope<'a> {
-    executor: Executor,
+    executor: BackgroundExecutor,
     futures: Vec<Pin<Box<dyn Future<Output = ()> + Send + 'static>>>,
     tx: Option<mpsc::Sender<()>>,
     rx: mpsc::Receiver<()>,
@@ -270,7 +243,7 @@ pub struct Scope<'a> {
 }
 
 impl<'a> Scope<'a> {
-    fn new(executor: Executor) -> Self {
+    fn new(executor: BackgroundExecutor) -> Self {
         let (tx, rx) = mpsc::channel(1);
         Self {
             executor,

crates/gpui2/src/gpui2.rs

@@ -68,24 +68,20 @@ use derive_more::{Deref, DerefMut};
 use std::{
     any::{Any, TypeId},
     borrow::{Borrow, BorrowMut},
-    mem,
     ops::{Deref, DerefMut},
-    sync::Arc,
 };
 use taffy::TaffyLayoutEngine;
 
-type AnyBox = Box<dyn Any + Send>;
+type AnyBox = Box<dyn Any>;
 
 pub trait Context {
     type ModelContext<'a, T>;
     type Result<T>;
 
-    fn build_model<T>(
+    fn build_model<T: 'static>(
         &mut self,
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
-    ) -> Self::Result<Model<T>>
+    ) -> Self::Result<Model<T>>;
-    where
-        T: 'static + Send;
 
     fn update_model<T: 'static, R>(
         &mut self,
@@ -102,7 +98,7 @@ pub trait VisualContext: Context {
         build_view_state: impl FnOnce(&mut Self::ViewContext<'_, '_, V>) -> V,
     ) -> Self::Result<View<V>>
     where
-        V: 'static + Send;
+        V: 'static;
 
     fn update_view<V: 'static, R>(
         &mut self,
@@ -127,100 +123,6 @@ pub enum GlobalKey {
     Type(TypeId),
 }
 
-#[repr(transparent)]
-pub struct MainThread<T>(T);
-
-impl<T> Deref for MainThread<T> {
-    type Target = T;
-
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-impl<T> DerefMut for MainThread<T> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
-    }
-}
-
-impl<C: Context> Context for MainThread<C> {
-    type ModelContext<'a, T> = MainThread<C::ModelContext<'a, T>>;
-    type Result<T> = C::Result<T>;
-
-    fn build_model<T>(
-        &mut self,
-        build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
-    ) -> Self::Result<Model<T>>
-    where
-        T: 'static + Send,
-    {
-        self.0.build_model(|cx| {
-            let cx = unsafe {
-                mem::transmute::<
-                    &mut C::ModelContext<'_, T>,
-                    &mut MainThread<C::ModelContext<'_, T>>,
-                >(cx)
-            };
-            build_model(cx)
-        })
-    }
-
-    fn update_model<T: 'static, R>(
-        &mut self,
-        handle: &Model<T>,
-        update: impl FnOnce(&mut T, &mut Self::ModelContext<'_, T>) -> R,
-    ) -> Self::Result<R> {
-        self.0.update_model(handle, |entity, cx| {
-            let cx = unsafe {
-                mem::transmute::<
-                    &mut C::ModelContext<'_, T>,
-                    &mut MainThread<C::ModelContext<'_, T>>,
-                >(cx)
-            };
-            update(entity, cx)
-        })
-    }
-}
-
-impl<C: VisualContext> VisualContext for MainThread<C> {
-    type ViewContext<'a, 'w, V> = MainThread<C::ViewContext<'a, 'w, V>>;
-
-    fn build_view<V>(
-        &mut self,
-        build_view_state: impl FnOnce(&mut Self::ViewContext<'_, '_, V>) -> V,
-    ) -> Self::Result<View<V>>
-    where
-        V: 'static + Send,
-    {
-        self.0.build_view(|cx| {
-            let cx = unsafe {
-                mem::transmute::<
-                    &mut C::ViewContext<'_, '_, V>,
-                    &mut MainThread<C::ViewContext<'_, '_, V>>,
-                >(cx)
-            };
-            build_view_state(cx)
-        })
-    }
-
-    fn update_view<V: 'static, R>(
-        &mut self,
-        view: &View<V>,
-        update: impl FnOnce(&mut V, &mut Self::ViewContext<'_, '_, V>) -> R,
-    ) -> Self::Result<R> {
-        self.0.update_view(view, |view_state, cx| {
-            let cx = unsafe {
-                mem::transmute::<
-                    &mut C::ViewContext<'_, '_, V>,
-                    &mut MainThread<C::ViewContext<'_, '_, V>>,
-                >(cx)
-            };
-            update(view_state, cx)
-        })
-    }
-}
-
 pub trait BorrowAppContext {
     fn with_text_style<F, R>(&mut self, style: TextStyleRefinement, f: F) -> R
     where
@@ -333,32 +235,3 @@ impl<'a, T> DerefMut for Reference<'a, T> {
         }
     }
 }
-
-pub(crate) struct MainThreadOnly<T: ?Sized> {
-    executor: Executor,
-    value: Arc<T>,
-}
-
-impl<T: ?Sized> Clone for MainThreadOnly<T> {
-    fn clone(&self) -> Self {
-        Self {
-            executor: self.executor.clone(),
-            value: self.value.clone(),
-        }
-    }
-}
-
-/// Allows a value to be accessed only on the main thread, allowing a non-`Send` type
-/// to become `Send`.
-impl<T: 'static + ?Sized> MainThreadOnly<T> {
-    pub(crate) fn new(value: Arc<T>, executor: Executor) -> Self {
-        Self { executor, value }
-    }
-
-    pub(crate) fn borrow_on_main_thread(&self) -> &T {
-        assert!(self.executor.is_main_thread());
-        &self.value
-    }
-}
-
-unsafe impl<T: ?Sized> Send for MainThreadOnly<T> {}

crates/gpui2/src/interactive.rs

@@ -50,7 +50,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
     fn on_mouse_down(
         mut self,
         button: MouseButton,
-        handler: impl Fn(&mut V, &MouseDownEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &MouseDownEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -71,7 +71,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
     fn on_mouse_up(
         mut self,
         button: MouseButton,
-        handler: impl Fn(&mut V, &MouseUpEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &MouseUpEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -92,7 +92,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
     fn on_mouse_down_out(
         mut self,
         button: MouseButton,
-        handler: impl Fn(&mut V, &MouseDownEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &MouseDownEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -113,7 +113,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
     fn on_mouse_up_out(
         mut self,
         button: MouseButton,
-        handler: impl Fn(&mut V, &MouseUpEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &MouseUpEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -133,7 +133,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
 
     fn on_mouse_move(
         mut self,
-        handler: impl Fn(&mut V, &MouseMoveEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &MouseMoveEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -150,7 +150,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
 
     fn on_scroll_wheel(
         mut self,
-        handler: impl Fn(&mut V, &ScrollWheelEvent, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &ScrollWheelEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -178,7 +178,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
 
     fn on_action<A: 'static>(
         mut self,
-        listener: impl Fn(&mut V, &A, DispatchPhase, &mut ViewContext<V>) + Send + 'static,
+        listener: impl Fn(&mut V, &A, DispatchPhase, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -196,7 +196,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
 
     fn on_key_down(
         mut self,
-        listener: impl Fn(&mut V, &KeyDownEvent, DispatchPhase, &mut ViewContext<V>) + Send + 'static,
+        listener: impl Fn(&mut V, &KeyDownEvent, DispatchPhase, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -214,7 +214,7 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
 
     fn on_key_up(
         mut self,
-        listener: impl Fn(&mut V, &KeyUpEvent, DispatchPhase, &mut ViewContext<V>) + Send + 'static,
+        listener: impl Fn(&mut V, &KeyUpEvent, DispatchPhase, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -258,9 +258,9 @@ pub trait StatelessInteractive<V: 'static>: Element<V> {
         self
     }
 
-    fn on_drop<W: 'static + Send>(
+    fn on_drop<W: 'static>(
         mut self,
-        listener: impl Fn(&mut V, View<W>, &mut ViewContext<V>) + Send + 'static,
+        listener: impl Fn(&mut V, View<W>, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -303,7 +303,7 @@ pub trait StatefulInteractive<V: 'static>: StatelessInteractive<V> {
 
     fn on_click(
         mut self,
-        listener: impl Fn(&mut V, &ClickEvent, &mut ViewContext<V>) + Send + 'static,
+        listener: impl Fn(&mut V, &ClickEvent, &mut ViewContext<V>) + 'static,
     ) -> Self
     where
         Self: Sized,
@@ -316,11 +316,11 @@ pub trait StatefulInteractive<V: 'static>: StatelessInteractive<V> {
 
     fn on_drag<W>(
         mut self,
-        listener: impl Fn(&mut V, &mut ViewContext<V>) -> View<W> + Send + 'static,
+        listener: impl Fn(&mut V, &mut ViewContext<V>) -> View<W> + 'static,
     ) -> Self
     where
         Self: Sized,
-        W: 'static + Send + Render,
+        W: 'static + Render,
     {
         debug_assert!(
             self.stateful_interaction().drag_listener.is_none(),
@@ -335,7 +335,7 @@ pub trait StatefulInteractive<V: 'static>: StatelessInteractive<V> {
     }
 }
 
-pub trait ElementInteraction<V: 'static>: 'static + Send {
+pub trait ElementInteraction<V: 'static>: 'static {
     fn as_stateless(&self) -> &StatelessInteraction<V>;
     fn as_stateless_mut(&mut self) -> &mut StatelessInteraction<V>;
     fn as_stateful(&self) -> Option<&StatefulInteraction<V>>;
@@ -672,7 +672,7 @@ impl<V> From<ElementId> for StatefulInteraction<V> {
     }
 }
 
-type DropListener<V> = dyn Fn(&mut V, AnyView, &mut ViewContext<V>) + 'static + Send;
+type DropListener<V> = dyn Fn(&mut V, AnyView, &mut ViewContext<V>) + 'static;
 
 pub struct StatelessInteraction<V> {
     pub dispatch_context: DispatchContext,
@@ -1077,32 +1077,25 @@ pub struct FocusEvent {
 }
 
 pub type MouseDownListener<V> = Box<
-    dyn Fn(&mut V, &MouseDownEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>)
+    dyn Fn(&mut V, &MouseDownEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>) + 'static,
-        + Send
-        + 'static,
 >;
 pub type MouseUpListener<V> = Box<
-    dyn Fn(&mut V, &MouseUpEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>)
+    dyn Fn(&mut V, &MouseUpEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>) + 'static,
-        + Send
-        + 'static,
 >;
 
 pub type MouseMoveListener<V> = Box<
-    dyn Fn(&mut V, &MouseMoveEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>)
+    dyn Fn(&mut V, &MouseMoveEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>) + 'static,
-        + Send
-        + 'static,
 >;
 
 pub type ScrollWheelListener<V> = Box<
     dyn Fn(&mut V, &ScrollWheelEvent, &Bounds<Pixels>, DispatchPhase, &mut ViewContext<V>)
-        + Send
         + 'static,
 >;
 
-pub type ClickListener<V> = Box<dyn Fn(&mut V, &ClickEvent, &mut ViewContext<V>) + Send + 'static>;
+pub type ClickListener<V> = Box<dyn Fn(&mut V, &ClickEvent, &mut ViewContext<V>) + 'static>;
 
 pub(crate) type DragListener<V> =
-    Box<dyn Fn(&mut V, Point<Pixels>, &mut ViewContext<V>) -> AnyDrag + Send + 'static>;
+    Box<dyn Fn(&mut V, Point<Pixels>, &mut ViewContext<V>) -> AnyDrag + 'static>;
 
 pub type KeyListener<V> = Box<
     dyn Fn(
@@ -1112,6 +1105,5 @@ pub type KeyListener<V> = Box<
             DispatchPhase,
             &mut ViewContext<V>,
         ) -> Option<Box<dyn Action>>
-        + Send
         + 'static,
 >;

crates/gpui2/src/platform.rs

@@ -5,9 +5,9 @@ mod mac;
 mod test;
 
 use crate::{
-    AnyWindowHandle, Bounds, DevicePixels, Executor, Font, FontId, FontMetrics, FontRun,
+    AnyWindowHandle, BackgroundExecutor, Bounds, DevicePixels, Font, FontId, FontMetrics, FontRun,
-    GlobalPixels, GlyphId, InputEvent, LineLayout, Pixels, Point, RenderGlyphParams,
+    ForegroundExecutor, GlobalPixels, GlyphId, InputEvent, LineLayout, Pixels, Point,
-    RenderImageParams, RenderSvgParams, Result, Scene, SharedString, Size,
+    RenderGlyphParams, RenderImageParams, RenderSvgParams, Result, Scene, SharedString, Size,
 };
 use anyhow::anyhow;
 use async_task::Runnable;
@@ -35,12 +35,13 @@ pub use test::*;
 pub use time::UtcOffset;
 
 #[cfg(target_os = "macos")]
-pub(crate) fn current_platform() -> Arc<dyn Platform> {
+pub(crate) fn current_platform() -> Rc<dyn Platform> {
-    Arc::new(MacPlatform::new())
+    Rc::new(MacPlatform::new())
 }
 
 pub(crate) trait Platform: 'static {
-    fn executor(&self) -> Executor;
+    fn background_executor(&self) -> BackgroundExecutor;
+    fn foreground_executor(&self) -> ForegroundExecutor;
     fn text_system(&self) -> Arc<dyn PlatformTextSystem>;
 
     fn run(&self, on_finish_launching: Box<dyn 'static + FnOnce()>);

crates/gpui2/src/platform/mac/platform.rs

@@ -1,9 +1,9 @@
 use super::BoolExt;
 use crate::{
-    AnyWindowHandle, ClipboardItem, CursorStyle, DisplayId, Executor, InputEvent, MacDispatcher,
+    AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, DisplayId, ForegroundExecutor,
-    MacDisplay, MacDisplayLinker, MacTextSystem, MacWindow, PathPromptOptions, Platform,
+    InputEvent, MacDispatcher, MacDisplay, MacDisplayLinker, MacTextSystem, MacWindow,
-    PlatformDisplay, PlatformTextSystem, PlatformWindow, Result, SemanticVersion, VideoTimestamp,
+    PathPromptOptions, Platform, PlatformDisplay, PlatformTextSystem, PlatformWindow, Result,
-    WindowOptions,
+    SemanticVersion, VideoTimestamp, WindowOptions,
 };
 use anyhow::anyhow;
 use block::ConcreteBlock;
@@ -143,7 +143,8 @@ unsafe fn build_classes() {
 pub struct MacPlatform(Mutex<MacPlatformState>);
 
 pub struct MacPlatformState {
-    executor: Executor,
+    background_executor: BackgroundExecutor,
+    foreground_executor: ForegroundExecutor,
     text_system: Arc<MacTextSystem>,
     display_linker: MacDisplayLinker,
     pasteboard: id,
@@ -164,8 +165,10 @@ pub struct MacPlatformState {
 
 impl MacPlatform {
     pub fn new() -> Self {
+        let dispatcher = Arc::new(MacDispatcher);
         Self(Mutex::new(MacPlatformState {
-            executor: Executor::new(Arc::new(MacDispatcher)),
+            background_executor: BackgroundExecutor::new(dispatcher.clone()),
+            foreground_executor: ForegroundExecutor::new(dispatcher.clone()),
             text_system: Arc::new(MacTextSystem::new()),
             display_linker: MacDisplayLinker::new(),
             pasteboard: unsafe { NSPasteboard::generalPasteboard(nil) },
@@ -345,8 +348,12 @@ impl MacPlatform {
 }
 
 impl Platform for MacPlatform {
-    fn executor(&self) -> Executor {
+    fn background_executor(&self) -> BackgroundExecutor {
-        self.0.lock().executor.clone()
+        self.0.lock().background_executor.clone()
+    }
+
+    fn foreground_executor(&self) -> crate::ForegroundExecutor {
+        self.0.lock().foreground_executor.clone()
     }
 
     fn text_system(&self) -> Arc<dyn PlatformTextSystem> {
@@ -457,6 +464,10 @@ impl Platform for MacPlatform {
         }
     }
 
+    // fn add_status_item(&self, _handle: AnyWindowHandle) -> Box<dyn platform::Window> {
+    //     Box::new(StatusItem::add(self.fonts()))
+    // }
+
     fn displays(&self) -> Vec<Rc<dyn PlatformDisplay>> {
         MacDisplay::all()
             .into_iter()
@@ -464,10 +475,6 @@ impl Platform for MacPlatform {
             .collect()
     }
 
-    // fn add_status_item(&self, _handle: AnyWindowHandle) -> Box<dyn platform::Window> {
-    //     Box::new(StatusItem::add(self.fonts()))
-    // }
-
     fn display(&self, id: DisplayId) -> Option<Rc<dyn PlatformDisplay>> {
         MacDisplay::find_by_id(id).map(|screen| Rc::new(screen) as Rc<_>)
     }
@@ -481,7 +488,7 @@ impl Platform for MacPlatform {
         handle: AnyWindowHandle,
         options: WindowOptions,
     ) -> Box<dyn PlatformWindow> {
-        Box::new(MacWindow::open(handle, options, self.executor()))
+        Box::new(MacWindow::open(handle, options, self.foreground_executor()))
     }
 
     fn set_display_link_output_callback(
@@ -589,8 +596,8 @@ impl Platform for MacPlatform {
             let path = path.to_path_buf();
             self.0
                 .lock()
-                .executor
+                .background_executor
-                .spawn_on_main_local(async move {
+                .spawn(async move {
                     let full_path = ns_string(path.to_str().unwrap_or(""));
                     let root_full_path = ns_string("");
                     let workspace: id = msg_send![class!(NSWorkspace), sharedWorkspace];
@@ -674,23 +681,6 @@ impl Platform for MacPlatform {
         }
     }
 
-    fn path_for_auxiliary_executable(&self, name: &str) -> Result<PathBuf> {
-        unsafe {
-            let bundle: id = NSBundle::mainBundle();
-            if bundle.is_null() {
-                Err(anyhow!("app is not running inside a bundle"))
-            } else {
-                let name = ns_string(name);
-                let url: id = msg_send![bundle, URLForAuxiliaryExecutable: name];
-                if url.is_null() {
-                    Err(anyhow!("resource not found"))
-                } else {
-                    ns_url_to_path(url)
-                }
-            }
-        }
-    }
-
     // fn on_menu_command(&self, callback: Box<dyn FnMut(&dyn Action)>) {
     //     self.0.lock().menu_command = Some(callback);
     // }
@@ -717,6 +707,23 @@ impl Platform for MacPlatform {
     //     }
     // }
 
+    fn path_for_auxiliary_executable(&self, name: &str) -> Result<PathBuf> {
+        unsafe {
+            let bundle: id = NSBundle::mainBundle();
+            if bundle.is_null() {
+                Err(anyhow!("app is not running inside a bundle"))
+            } else {
+                let name = ns_string(name);
+                let url: id = msg_send![bundle, URLForAuxiliaryExecutable: name];
+                if url.is_null() {
+                    Err(anyhow!("resource not found"))
+                } else {
+                    ns_url_to_path(url)
+                }
+            }
+        }
+    }
+
     fn set_cursor_style(&self, style: CursorStyle) {
         unsafe {
             let new_cursor: id = match style {

crates/gpui2/src/platform/mac/window.rs

@@ -1,10 +1,10 @@
 use super::{display_bounds_from_native, ns_string, MacDisplay, MetalRenderer, NSRange};
 use crate::{
-    display_bounds_to_native, point, px, size, AnyWindowHandle, Bounds, Executor, ExternalPaths,
+    display_bounds_to_native, point, px, size, AnyWindowHandle, Bounds, ExternalPaths,
-    FileDropEvent, GlobalPixels, InputEvent, KeyDownEvent, Keystroke, Modifiers,
+    FileDropEvent, ForegroundExecutor, GlobalPixels, InputEvent, KeyDownEvent, Keystroke,
-    ModifiersChangedEvent, MouseButton, MouseDownEvent, MouseMoveEvent, MouseUpEvent, Pixels,
+    Modifiers, ModifiersChangedEvent, MouseButton, MouseDownEvent, MouseMoveEvent, MouseUpEvent,
-    PlatformAtlas, PlatformDisplay, PlatformInputHandler, PlatformWindow, Point, Scene, Size,
+    Pixels, PlatformAtlas, PlatformDisplay, PlatformInputHandler, PlatformWindow, Point, Scene,
-    Timer, WindowAppearance, WindowBounds, WindowKind, WindowOptions, WindowPromptLevel,
+    Size, Timer, WindowAppearance, WindowBounds, WindowKind, WindowOptions, WindowPromptLevel,
 };
 use block::ConcreteBlock;
 use cocoa::{
@@ -315,7 +315,7 @@ struct InsertText {
 
 struct MacWindowState {
     handle: AnyWindowHandle,
-    executor: Executor,
+    executor: ForegroundExecutor,
     native_window: id,
     renderer: MetalRenderer,
     scene_to_render: Option<Scene>,
@@ -451,7 +451,11 @@ unsafe impl Send for MacWindowState {}
 pub struct MacWindow(Arc<Mutex<MacWindowState>>);
 
 impl MacWindow {
-    pub fn open(handle: AnyWindowHandle, options: WindowOptions, executor: Executor) -> Self {
+    pub fn open(
+        handle: AnyWindowHandle,
+        options: WindowOptions,
+        executor: ForegroundExecutor,
+    ) -> Self {
         unsafe {
             let pool = NSAutoreleasePool::new(nil);
 
@@ -674,13 +678,10 @@ impl MacWindow {
 
 impl Drop for MacWindow {
     fn drop(&mut self) {
-        let this = self.0.clone();
+        let native_window = self.0.lock().native_window;
-        let executor = self.0.lock().executor.clone();
+        unsafe {
-        executor
+            native_window.close();
-            .run_on_main(move || unsafe {
+        }
-                this.lock().native_window.close();
-            })
-            .detach();
     }
 }
 
@@ -807,7 +808,7 @@ impl PlatformWindow for MacWindow {
             let native_window = self.0.lock().native_window;
             let executor = self.0.lock().executor.clone();
             executor
-                .spawn_on_main_local(async move {
+                .spawn(async move {
                     let _: () = msg_send![
                         alert,
                         beginSheetModalForWindow: native_window
@@ -824,7 +825,7 @@ impl PlatformWindow for MacWindow {
         let window = self.0.lock().native_window;
         let executor = self.0.lock().executor.clone();
         executor
-            .spawn_on_main_local(async move {
+            .spawn(async move {
                 unsafe {
                     let _: () = msg_send![window, makeKeyAndOrderFront: nil];
                 }
@@ -872,25 +873,17 @@ impl PlatformWindow for MacWindow {
     fn zoom(&self) {
         let this = self.0.lock();
         let window = this.native_window;
-        this.executor
+        unsafe {
-            .spawn_on_main_local(async move {
+            window.zoom_(nil);
-                unsafe {
+        }
-                    window.zoom_(nil);
-                }
-            })
-            .detach();
     }
 
     fn toggle_full_screen(&self) {
         let this = self.0.lock();
         let window = this.native_window;
-        this.executor
+        unsafe {
-            .spawn_on_main_local(async move {
+            window.toggleFullScreen_(nil);
-                unsafe {
+        }
-                    window.toggleFullScreen_(nil);
-                }
-            })
-            .detach();
     }
 
     fn on_input(&self, callback: Box<dyn FnMut(InputEvent) -> bool>) {
@@ -1189,7 +1182,7 @@ extern "C" fn handle_view_event(this: &Object, _: Sel, native_event: id) {
                 lock.synthetic_drag_counter += 1;
                 let executor = lock.executor.clone();
                 executor
-                    .spawn_on_main_local(synthetic_drag(
+                    .spawn(synthetic_drag(
                         weak_window_state,
                         lock.synthetic_drag_counter,
                         event.clone(),
@@ -1317,7 +1310,7 @@ extern "C" fn window_did_change_key_status(this: &Object, selector: Sel, _: id)
     let executor = lock.executor.clone();
     drop(lock);
     executor
-        .spawn_on_main_local(async move {
+        .spawn(async move {
             let mut lock = window_state.as_ref().lock();
             if let Some(mut callback) = lock.activate_callback.take() {
                 drop(lock);

crates/gpui2/src/platform/test/dispatcher.rs

@@ -215,58 +215,3 @@ impl PlatformDispatcher for TestDispatcher {
         Some(self)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::Executor;
-    use std::sync::Arc;
-
-    #[test]
-    fn test_dispatch() {
-        let dispatcher = TestDispatcher::new(StdRng::seed_from_u64(0));
-        let executor = Executor::new(Arc::new(dispatcher));
-
-        let result = executor.block(async { executor.run_on_main(|| 1).await });
-        assert_eq!(result, 1);
-
-        let result = executor.block({
-            let executor = executor.clone();
-            async move {
-                executor
-                    .spawn_on_main({
-                        let executor = executor.clone();
-                        assert!(executor.is_main_thread());
-                        || async move {
-                            assert!(executor.is_main_thread());
-                            let result = executor
-                                .spawn({
-                                    let executor = executor.clone();
-                                    async move {
-                                        assert!(!executor.is_main_thread());
-
-                                        let result = executor
-                                            .spawn_on_main({
-                                                let executor = executor.clone();
-                                                || async move {
-                                                    assert!(executor.is_main_thread());
-                                                    2
-                                                }
-                                            })
-                                            .await;
-
-                                        assert!(!executor.is_main_thread());
-                                        result
-                                    }
-                                })
-                                .await;
-                            assert!(executor.is_main_thread());
-                            result
-                        }
-                    })
-                    .await
-            }
-        });
-        assert_eq!(result, 2);
-    }
-}

crates/gpui2/src/platform/test/platform.rs

@@ -1,21 +1,29 @@
-use crate::{DisplayId, Executor, Platform, PlatformTextSystem};
+use crate::{BackgroundExecutor, DisplayId, ForegroundExecutor, Platform, PlatformTextSystem};
 use anyhow::{anyhow, Result};
 use std::sync::Arc;
 
 pub struct TestPlatform {
-    executor: Executor,
+    background_executor: BackgroundExecutor,
+    foreground_executor: ForegroundExecutor,
 }
 
 impl TestPlatform {
-    pub fn new(executor: Executor) -> Self {
+    pub fn new(executor: BackgroundExecutor, foreground_executor: ForegroundExecutor) -> Self {
-        TestPlatform { executor }
+        TestPlatform {
+            background_executor: executor,
+            foreground_executor,
+        }
     }
 }
 
 // todo!("implement out what our tests needed in GPUI 1")
 impl Platform for TestPlatform {
-    fn executor(&self) -> Executor {
+    fn background_executor(&self) -> BackgroundExecutor {
-        self.executor.clone()
+        self.background_executor.clone()
+    }
+
+    fn foreground_executor(&self) -> ForegroundExecutor {
+        self.foreground_executor.clone()
     }
 
     fn text_system(&self) -> Arc<dyn PlatformTextSystem> {

crates/gpui2/src/subscription.rs

@@ -21,8 +21,8 @@ struct SubscriberSetState<EmitterKey, Callback> {
 
 impl<EmitterKey, Callback> SubscriberSet<EmitterKey, Callback>
 where
-    EmitterKey: 'static + Send + Ord + Clone + Debug,
+    EmitterKey: 'static + Ord + Clone + Debug,
-    Callback: 'static + Send,
+    Callback: 'static,
 {
     pub fn new() -> Self {
         Self(Arc::new(Mutex::new(SubscriberSetState {
@@ -96,7 +96,7 @@ where
 
 #[must_use]
 pub struct Subscription {
-    unsubscribe: Option<Box<dyn FnOnce() + Send + 'static>>,
+    unsubscribe: Option<Box<dyn FnOnce() + 'static>>,
 }
 
 impl Subscription {

crates/gpui2/src/view.rs

@@ -4,10 +4,13 @@ use crate::{
     Size, ViewContext, VisualContext, WeakModel, WindowContext,
 };
 use anyhow::{Context, Result};
-use std::{any::TypeId, marker::PhantomData};
+use std::{
+    any::{Any, TypeId},
+    marker::PhantomData,
+};
 
 pub trait Render: 'static + Sized {
-    type Element: Element<Self> + 'static + Send;
+    type Element: Element<Self> + 'static;
 
     fn render(&mut self, cx: &mut ViewContext<Self>) -> Self::Element;
 }
@@ -163,7 +166,7 @@ impl<V: Render, ParentV: 'static> Component<ParentV> for EraseViewState<V, Paren
 }
 
 impl<V: Render, ParentV: 'static> Element<ParentV> for EraseViewState<V, ParentV> {
-    type ElementState = AnyBox;
+    type ElementState = Box<dyn Any>;
 
     fn id(&self) -> Option<crate::ElementId> {
         Element::id(&self.view)
@@ -343,7 +346,7 @@ impl<V: Render> From<View<V>> for AnyView {
 }
 
 impl<ParentViewState: 'static> Element<ParentViewState> for AnyView {
-    type ElementState = AnyBox;
+    type ElementState = Box<dyn Any>;
 
     fn id(&self) -> Option<ElementId> {
         Some(self.model.entity_id.into())

crates/gpui2/src/window.rs

@@ -3,12 +3,11 @@ use crate::{
     Bounds, BoxShadow, Context, Corners, DevicePixels, DispatchContext, DisplayId, Edges, Effect,
     Entity, EntityId, EventEmitter, FileDropEvent, FocusEvent, FontId, GlobalElementId, GlyphId,
     Hsla, ImageData, InputEvent, IsZero, KeyListener, KeyMatch, KeyMatcher, Keystroke, LayoutId,
-    MainThread, MainThreadOnly, Model, ModelContext, Modifiers, MonochromeSprite, MouseButton,
+    Model, ModelContext, Modifiers, MonochromeSprite, MouseButton, MouseDownEvent, MouseMoveEvent,
-    MouseDownEvent, MouseMoveEvent, MouseUpEvent, Path, Pixels, PlatformAtlas, PlatformWindow,
+    MouseUpEvent, Path, Pixels, PlatformAtlas, PlatformWindow, Point, PolychromeSprite, Quad,
-    Point, PolychromeSprite, Quad, Reference, RenderGlyphParams, RenderImageParams,
+    Reference, RenderGlyphParams, RenderImageParams, RenderSvgParams, ScaledPixels, SceneBuilder,
-    RenderSvgParams, ScaledPixels, SceneBuilder, Shadow, SharedString, Size, Style, Subscription,
+    Shadow, SharedString, Size, Style, Subscription, TaffyLayoutEngine, Task, Underline,
-    TaffyLayoutEngine, Task, Underline, UnderlineStyle, View, VisualContext, WeakModel, WeakView,
+    UnderlineStyle, View, VisualContext, WeakModel, WeakView, WindowOptions, SUBPIXEL_VARIANTS,
-    WindowOptions, SUBPIXEL_VARIANTS,
 };
 use anyhow::Result;
 use collections::HashMap;
@@ -52,7 +51,7 @@ pub enum DispatchPhase {
     Capture,
 }
 
-type AnyListener = Box<dyn Fn(&dyn Any, DispatchPhase, &mut WindowContext) + Send + 'static>;
+type AnyListener = Box<dyn Fn(&dyn Any, DispatchPhase, &mut WindowContext) + 'static>;
 type AnyKeyListener = Box<
     dyn Fn(
             &dyn Any,
@@ -60,10 +59,9 @@ type AnyKeyListener = Box<
             DispatchPhase,
             &mut WindowContext,
         ) -> Option<Box<dyn Action>>
-        + Send
         + 'static,
 >;
-type AnyFocusListener = Box<dyn Fn(&FocusEvent, &mut WindowContext) + Send + 'static>;
+type AnyFocusListener = Box<dyn Fn(&FocusEvent, &mut WindowContext) + 'static>;
 
 slotmap::new_key_type! { pub struct FocusId; }
 
@@ -159,7 +157,7 @@ impl Drop for FocusHandle {
 // Holds the state for a specific window.
 pub struct Window {
     handle: AnyWindowHandle,
-    platform_window: MainThreadOnly<Box<dyn PlatformWindow>>,
+    platform_window: Box<dyn PlatformWindow>,
     display_id: DisplayId,
     sprite_atlas: Arc<dyn PlatformAtlas>,
     rem_size: Pixels,
@@ -194,7 +192,7 @@ impl Window {
     pub(crate) fn new(
         handle: AnyWindowHandle,
         options: WindowOptions,
-        cx: &mut MainThread<AppContext>,
+        cx: &mut AppContext,
     ) -> Self {
         let platform_window = cx.platform().open_window(handle, options);
         let display_id = platform_window.display().id();
@@ -209,12 +207,7 @@ impl Window {
                     cx.window.scale_factor = scale_factor;
                     cx.window.scene_builder = SceneBuilder::new();
                     cx.window.content_size = content_size;
-                    cx.window.display_id = cx
+                    cx.window.display_id = cx.window.platform_window.display().id();
-                        .window
-                        .platform_window
-                        .borrow_on_main_thread()
-                        .display()
-                        .id();
                     cx.window.dirty = true;
                 })
                 .log_err();
@@ -230,8 +223,6 @@ impl Window {
             })
         });
 
-        let platform_window = MainThreadOnly::new(Arc::new(platform_window), cx.executor.clone());
-
         Window {
             handle,
             platform_window,
@@ -378,26 +369,6 @@ impl<'a, 'w> WindowContext<'a, 'w> {
         self.notify();
     }
 
-    /// Schedule the given closure to be run on the main thread. It will be invoked with
-    /// a `MainThread<WindowContext>`, which provides access to platform-specific functionality
-    /// of the window.
-    pub fn run_on_main<R>(
-        &mut self,
-        f: impl FnOnce(&mut MainThread<WindowContext<'_, '_>>) -> R + Send + 'static,
-    ) -> Task<Result<R>>
-    where
-        R: Send + 'static,
-    {
-        if self.executor.is_main_thread() {
-            Task::ready(Ok(f(unsafe {
-                mem::transmute::<&mut Self, &mut MainThread<Self>>(self)
-            })))
-        } else {
-            let id = self.window.handle.id;
-            self.app.run_on_main(move |cx| cx.update_window(id, f))
-        }
-    }
-
     /// Create an `AsyncWindowContext`, which has a static lifetime and can be held across
     /// await points in async code.
     pub fn to_async(&self) -> AsyncWindowContext {
@@ -408,44 +379,39 @@ impl<'a, 'w> WindowContext<'a, 'w> {
     pub fn on_next_frame(&mut self, f: impl FnOnce(&mut WindowContext) + Send + 'static) {
         let f = Box::new(f);
         let display_id = self.window.display_id;
-        self.run_on_main(move |cx| {
-            if let Some(callbacks) = cx.next_frame_callbacks.get_mut(&display_id) {
-                callbacks.push(f);
-                // If there was already a callback, it means that we already scheduled a frame.
-                if callbacks.len() > 1 {
-                    return;
-                }
-            } else {
-                let async_cx = cx.to_async();
-                cx.next_frame_callbacks.insert(display_id, vec![f]);
-                cx.platform().set_display_link_output_callback(
-                    display_id,
-                    Box::new(move |_current_time, _output_time| {
-                        let _ = async_cx.update(|cx| {
-                            let callbacks = cx
-                                .next_frame_callbacks
-                                .get_mut(&display_id)
-                                .unwrap()
-                                .drain(..)
-                                .collect::<Vec<_>>();
-                            for callback in callbacks {
-                                callback(cx);
-                            }
 
-                            cx.run_on_main(move |cx| {
+        if let Some(callbacks) = self.next_frame_callbacks.get_mut(&display_id) {
-                                if cx.next_frame_callbacks.get(&display_id).unwrap().is_empty() {
+            callbacks.push(f);
-                                    cx.platform().stop_display_link(display_id);
+            // If there was already a callback, it means that we already scheduled a frame.
-                                }
+            if callbacks.len() > 1 {
-                            })
+                return;
-                            .detach();
-                        });
-                    }),
-                );
             }
+        } else {
+            let async_cx = self.to_async();
+            self.next_frame_callbacks.insert(display_id, vec![f]);
+            self.platform().set_display_link_output_callback(
+                display_id,
+                Box::new(move |_current_time, _output_time| {
+                    let _ = async_cx.update(|cx| {
+                        let callbacks = cx
+                            .next_frame_callbacks
+                            .get_mut(&display_id)
+                            .unwrap()
+                            .drain(..)
+                            .collect::<Vec<_>>();
+                        for callback in callbacks {
+                            callback(cx);
+                        }
 
-            cx.platform().start_display_link(display_id);
+                        if cx.next_frame_callbacks.get(&display_id).unwrap().is_empty() {
-        })
+                            cx.platform().stop_display_link(display_id);
-        .detach();
+                        }
+                    });
+                }),
+            );
+        }
+
+        self.platform().start_display_link(display_id);
     }
 
     /// Spawn the future returned by the given closure on the application thread pool.
@@ -453,17 +419,16 @@ impl<'a, 'w> WindowContext<'a, 'w> {
     /// use within your future.
     pub fn spawn<Fut, R>(
         &mut self,
-        f: impl FnOnce(AnyWindowHandle, AsyncWindowContext) -> Fut + Send + 'static,
+        f: impl FnOnce(AnyWindowHandle, AsyncWindowContext) -> Fut,
     ) -> Task<R>
     where
-        R: Send + 'static,
+        R: 'static,
-        Fut: Future<Output = R> + Send + 'static,
+        Fut: Future<Output = R> + 'static,
     {
         let window = self.window.handle;
         self.app.spawn(move |app| {
             let cx = AsyncWindowContext::new(app, window);
-            let future = f(window, cx);
+            f(window, cx)
-            async move { future.await }
         })
     }
 
@@ -569,7 +534,7 @@ impl<'a, 'w> WindowContext<'a, 'w> {
     /// a specific need to register a global listener.
     pub fn on_mouse_event<Event: 'static>(
         &mut self,
-        handler: impl Fn(&Event, DispatchPhase, &mut WindowContext) + Send + 'static,
+        handler: impl Fn(&Event, DispatchPhase, &mut WindowContext) + 'static,
     ) {
         let order = self.window.z_index_stack.clone();
         self.window
@@ -906,14 +871,8 @@ impl<'a, 'w> WindowContext<'a, 'w> {
         self.window.root_view = Some(root_view);
         let scene = self.window.scene_builder.build();
 
-        self.run_on_main(|cx| {
+        self.window.platform_window.draw(scene);
-            cx.window
+        self.window.dirty = false;
-                .platform_window
-                .borrow_on_main_thread()
-                .draw(scene);
-            cx.window.dirty = false;
-        })
-        .detach();
     }
 
     fn start_frame(&mut self) {
@@ -1246,7 +1205,7 @@ impl Context for WindowContext<'_, '_> {
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
     ) -> Model<T>
     where
-        T: 'static + Send,
+        T: 'static,
     {
         let slot = self.app.entities.reserve();
         let model = build_model(&mut ModelContext::mutable(&mut *self.app, slot.downgrade()));
@@ -1276,7 +1235,7 @@ impl VisualContext for WindowContext<'_, '_> {
         build_view_state: impl FnOnce(&mut Self::ViewContext<'_, '_, V>) -> V,
     ) -> Self::Result<View<V>>
     where
-        V: 'static + Send,
+        V: 'static,
     {
         let slot = self.app.entities.reserve();
         let view = View {
@@ -1422,7 +1381,7 @@ pub trait BorrowWindow: BorrowMut<Window> + BorrowMut<AppContext> {
         f: impl FnOnce(Option<S>, &mut Self) -> (R, S),
     ) -> R
     where
-        S: 'static + Send,
+        S: 'static,
     {
         self.with_element_id(id, |global_id, cx| {
             if let Some(any) = cx
@@ -1460,7 +1419,7 @@ pub trait BorrowWindow: BorrowMut<Window> + BorrowMut<AppContext> {
         f: impl FnOnce(Option<S>, &mut Self) -> (R, S),
     ) -> R
     where
-        S: 'static + Send,
+        S: 'static,
     {
         if let Some(element_id) = element_id {
             self.with_element_state(element_id, f)
@@ -1772,30 +1731,13 @@ impl<'a, 'w, V: 'static> ViewContext<'a, 'w, V> {
         result
     }
 
-    pub fn run_on_main<R>(
-        &mut self,
-        view: &mut V,
-        f: impl FnOnce(&mut V, &mut MainThread<ViewContext<'_, '_, V>>) -> R + Send + 'static,
-    ) -> Task<Result<R>>
-    where
-        R: Send + 'static,
-    {
-        if self.executor.is_main_thread() {
-            let cx = unsafe { mem::transmute::<&mut Self, &mut MainThread<Self>>(self) };
-            Task::ready(Ok(f(view, cx)))
-        } else {
-            let view = self.view().upgrade().unwrap();
-            self.window_cx.run_on_main(move |cx| view.update(cx, f))
-        }
-    }
-
     pub fn spawn<Fut, R>(
         &mut self,
-        f: impl FnOnce(WeakView<V>, AsyncWindowContext) -> Fut + Send + 'static,
+        f: impl FnOnce(WeakView<V>, AsyncWindowContext) -> Fut,
     ) -> Task<R>
     where
-        R: Send + 'static,
+        R: 'static,
-        Fut: Future<Output = R> + Send + 'static,
+        Fut: Future<Output = R> + 'static,
     {
         let view = self.view();
         self.window_cx.spawn(move |_, cx| {
@@ -1833,7 +1775,7 @@ impl<'a, 'w, V: 'static> ViewContext<'a, 'w, V> {
 
     pub fn on_mouse_event<Event: 'static>(
         &mut self,
-        handler: impl Fn(&mut V, &Event, DispatchPhase, &mut ViewContext<V>) + Send + 'static,
+        handler: impl Fn(&mut V, &Event, DispatchPhase, &mut ViewContext<V>) + 'static,
     ) {
         let handle = self.view().upgrade().unwrap();
         self.window_cx.on_mouse_event(move |event, phase, cx| {
@@ -1862,13 +1804,10 @@ impl<'a, 'w, V> Context for ViewContext<'a, 'w, V> {
     type ModelContext<'b, U> = ModelContext<'b, U>;
     type Result<U> = U;
 
-    fn build_model<T>(
+    fn build_model<T: 'static>(
         &mut self,
         build_model: impl FnOnce(&mut Self::ModelContext<'_, T>) -> T,
-    ) -> Model<T>
+    ) -> Model<T> {
-    where
-        T: 'static + Send,
-    {
         self.window_cx.build_model(build_model)
     }
 
@@ -1884,7 +1823,7 @@ impl<'a, 'w, V> Context for ViewContext<'a, 'w, V> {
 impl<V: 'static> VisualContext for ViewContext<'_, '_, V> {
     type ViewContext<'a, 'w, V2> = ViewContext<'a, 'w, V2>;
 
-    fn build_view<W: 'static + Send>(
+    fn build_view<W: 'static>(
         &mut self,
         build_view: impl FnOnce(&mut Self::ViewContext<'_, '_, W>) -> W,
     ) -> Self::Result<View<W>> {

crates/language2/src/language2.rs

@@ -17,7 +17,7 @@ use futures::{
     future::{BoxFuture, Shared},
     FutureExt, TryFutureExt as _,
 };
-use gpui2::{AppContext, AsyncAppContext, Executor, Task};
+use gpui2::{AppContext, AsyncAppContext, BackgroundExecutor, Task};
 pub use highlight_map::HighlightMap;
 use lazy_static::lazy_static;
 use lsp2::{CodeActionKind, LanguageServerBinary};
@@ -631,7 +631,7 @@ pub struct LanguageRegistry {
     lsp_binary_paths: Mutex<
         HashMap<LanguageServerName, Shared<Task<Result<LanguageServerBinary, Arc<anyhow::Error>>>>>,
     >,
-    executor: Option<Executor>,
+    executor: Option<BackgroundExecutor>,
     lsp_binary_status_tx: LspBinaryStatusSender,
 }
 
@@ -680,7 +680,7 @@ impl LanguageRegistry {
         Self::new(Task::ready(()))
     }
 
-    pub fn set_executor(&mut self, executor: Executor) {
+    pub fn set_executor(&mut self, executor: BackgroundExecutor) {
         self.executor = Some(executor);
     }
 
@@ -916,7 +916,7 @@ impl LanguageRegistry {
                 }
 
                 let servers_tx = servers_tx.clone();
-                cx.executor()
+                cx.background_executor()
                     .spawn(async move {
                         if fake_server
                             .try_receive_notification::<lsp2::notification::Initialized>()

crates/lsp2/src/lsp2.rs

@@ -5,7 +5,7 @@ pub use lsp_types::*;
 use anyhow::{anyhow, Context, Result};
 use collections::HashMap;
 use futures::{channel::oneshot, io::BufWriter, AsyncRead, AsyncWrite, FutureExt};
-use gpui2::{AsyncAppContext, Executor, Task};
+use gpui2::{AsyncAppContext, BackgroundExecutor, Task};
 use parking_lot::Mutex;
 use postage::{barrier, prelude::Stream};
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
@@ -62,7 +62,7 @@ pub struct LanguageServer {
     notification_handlers: Arc<Mutex<HashMap<&'static str, NotificationHandler>>>,
     response_handlers: Arc<Mutex<Option<HashMap<usize, ResponseHandler>>>>,
     io_handlers: Arc<Mutex<HashMap<usize, IoHandler>>>,
-    executor: Executor,
+    executor: BackgroundExecutor,
     #[allow(clippy::type_complexity)]
     io_tasks: Mutex<Option<(Task<Option<()>>, Task<Option<()>>)>>,
     output_done_rx: Mutex<Option<barrier::Receiver>>,
@@ -248,7 +248,7 @@ impl LanguageServer {
             let (stdout, stderr) = futures::join!(stdout_input_task, stderr_input_task);
             stdout.or(stderr)
         });
-        let output_task = cx.executor().spawn({
+        let output_task = cx.background_executor().spawn({
             Self::handle_output(
                 stdin,
                 outbound_rx,
@@ -269,7 +269,7 @@ impl LanguageServer {
             code_action_kinds,
             next_id: Default::default(),
             outbound_tx,
-            executor: cx.executor().clone(),
+            executor: cx.background_executor().clone(),
             io_tasks: Mutex::new(Some((input_task, output_task))),
             output_done_rx: Mutex::new(Some(output_done_rx)),
             root_path: root_path.to_path_buf(),
@@ -670,10 +670,10 @@ impl LanguageServer {
                     match serde_json::from_str(params) {
                         Ok(params) => {
                             let response = f(params, cx.clone());
-                            cx.executor()
+                            cx.foreground_executor()
-                                .spawn_on_main({
+                                .spawn({
                                     let outbound_tx = outbound_tx.clone();
-                                    move || async move {
+                                    async move {
                                         let response = match response.await {
                                             Ok(result) => Response {
                                                 jsonrpc: JSON_RPC_VERSION,
@@ -769,7 +769,7 @@ impl LanguageServer {
         next_id: &AtomicUsize,
         response_handlers: &Mutex<Option<HashMap<usize, ResponseHandler>>>,
         outbound_tx: &channel::Sender<String>,
-        executor: &Executor,
+        executor: &BackgroundExecutor,
         params: T::Params,
     ) -> impl 'static + Future<Output = anyhow::Result<T::Result>>
     where
@@ -1048,7 +1048,7 @@ impl FakeLanguageServer {
                 let result = handler(params, cx.clone());
                 let responded_tx = responded_tx.clone();
                 async move {
-                    cx.executor().simulate_random_delay().await;
+                    cx.background_executor().simulate_random_delay().await;
                     let result = result.await;
                     responded_tx.unbounded_send(()).ok();
                     result

crates/project2/src/project2.rs

@@ -26,8 +26,8 @@ use futures::{
 };
 use globset::{Glob, GlobSet, GlobSetBuilder};
 use gpui2::{
-    AnyModel, AppContext, AsyncAppContext, Context, Entity, EventEmitter, Executor, Model,
+    AnyModel, AppContext, AsyncAppContext, BackgroundExecutor, Context, Entity, EventEmitter,
-    ModelContext, Task, WeakModel,
+    Model, ModelContext, Task, WeakModel,
 };
 use itertools::Itertools;
 use language2::{
@@ -207,7 +207,7 @@ impl DelayedDebounced {
 
         let previous_task = self.task.take();
         self.task = Some(cx.spawn(move |project, mut cx| async move {
-            let mut timer = cx.executor().timer(delay).fuse();
+            let mut timer = cx.background_executor().timer(delay).fuse();
             if let Some(previous_task) = previous_task {
                 previous_task.await;
             }
@@ -1453,7 +1453,7 @@ impl Project {
                             };
                             if client.send(initial_state).log_err().is_some() {
                                 let client = client.clone();
-                                cx.executor()
+                                cx.background_executor()
                                     .spawn(async move {
                                         let mut chunks = split_operations(operations).peekable();
                                         while let Some(chunk) = chunks.next() {
@@ -2436,7 +2436,7 @@ impl Project {
                                 Duration::from_secs(1);
 
                             let task = cx.spawn(move |this, mut cx| async move {
-                                cx.executor().timer(DISK_BASED_DIAGNOSTICS_DEBOUNCE).await;
+                                cx.background_executor().timer(DISK_BASED_DIAGNOSTICS_DEBOUNCE).await;
                                 if let Some(this) = this.upgrade() {
                                     this.update(&mut cx, |this, cx| {
                                         this.disk_based_diagnostics_finished(
@@ -3477,7 +3477,7 @@ impl Project {
             });
 
             const PROCESS_TIMEOUT: Duration = Duration::from_secs(5);
-            let mut timeout = cx.executor().timer(PROCESS_TIMEOUT).fuse();
+            let mut timeout = cx.background_executor().timer(PROCESS_TIMEOUT).fuse();
 
             let mut errored = false;
             if let Some(mut process) = process {
@@ -5741,7 +5741,7 @@ impl Project {
     async fn background_search(
         unnamed_buffers: Vec<Model<Buffer>>,
         opened_buffers: HashMap<Arc<Path>, (Model<Buffer>, BufferSnapshot)>,
-        executor: Executor,
+        executor: BackgroundExecutor,
         fs: Arc<dyn Fs>,
         workers: usize,
         query: SearchQuery,
@@ -6376,7 +6376,7 @@ impl Project {
             let snapshot =
                 worktree_handle.update(&mut cx, |tree, _| tree.as_local().unwrap().snapshot())?;
             let diff_bases_by_buffer = cx
-                .executor()
+                .background_executor()
                 .spawn(async move {
                     future_buffers
                         .into_iter()
@@ -7983,7 +7983,7 @@ impl Project {
             // Any incomplete buffers have open requests waiting. Request that the host sends
             // creates these buffers for us again to unblock any waiting futures.
             for id in incomplete_buffer_ids {
-                cx.executor()
+                cx.background_executor()
                     .spawn(client.request(proto::OpenBufferById { project_id, id }))
                     .detach();
             }
@@ -8438,7 +8438,7 @@ impl Project {
             let fs = self.fs.clone();
             cx.spawn(move |this, mut cx| async move {
                 let prettier_dir = match cx
-                    .executor()
+                    .background_executor()
                     .spawn(Prettier::locate(
                         worktree_path.zip(buffer_path).map(
                             |(worktree_root_path, starting_path)| LocateStart {

crates/project2/src/worktree.rs

@@ -22,7 +22,8 @@ use futures::{
 use fuzzy2::CharBag;
 use git::{DOT_GIT, GITIGNORE};
 use gpui2::{
-    AppContext, AsyncAppContext, Context, EventEmitter, Executor, Model, ModelContext, Task,
+    AppContext, AsyncAppContext, BackgroundExecutor, Context, EventEmitter, Model, ModelContext,
+    Task,
 };
 use language2::{
     proto::{
@@ -600,7 +601,7 @@ impl LocalWorktree {
                 .update(&mut cx, |t, cx| t.as_local().unwrap().load(&path, cx))?
                 .await?;
             let text_buffer = cx
-                .executor()
+                .background_executor()
                 .spawn(async move { text::Buffer::new(0, id, contents) })
                 .await;
             cx.build_model(|_| Buffer::build(text_buffer, diff_base, Some(Arc::new(file))))
@@ -888,7 +889,7 @@ impl LocalWorktree {
                 if let Some(repo) = snapshot.git_repositories.get(&*repo.work_directory) {
                     let repo = repo.repo_ptr.clone();
                     index_task = Some(
-                        cx.executor()
+                        cx.background_executor()
                             .spawn(async move { repo.lock().load_index_text(&repo_path) }),
                     );
                 }
@@ -3012,7 +3013,7 @@ struct BackgroundScanner {
     state: Mutex<BackgroundScannerState>,
     fs: Arc<dyn Fs>,
     status_updates_tx: UnboundedSender<ScanState>,
-    executor: Executor,
+    executor: BackgroundExecutor,
     scan_requests_rx: channel::Receiver<ScanRequest>,
     path_prefixes_to_scan_rx: channel::Receiver<Arc<Path>>,
     next_entry_id: Arc<AtomicUsize>,
@@ -3032,7 +3033,7 @@ impl BackgroundScanner {
         next_entry_id: Arc<AtomicUsize>,
         fs: Arc<dyn Fs>,
         status_updates_tx: UnboundedSender<ScanState>,
-        executor: Executor,
+        executor: BackgroundExecutor,
         scan_requests_rx: channel::Receiver<ScanRequest>,
         path_prefixes_to_scan_rx: channel::Receiver<Arc<Path>>,
     ) -> Self {

crates/rpc2/src/conn.rs

@@ -34,7 +34,7 @@ impl Connection {
 
     #[cfg(any(test, feature = "test-support"))]
     pub fn in_memory(
-        executor: gpui2::Executor,
+        executor: gpui2::BackgroundExecutor,
     ) -> (Self, Self, std::sync::Arc<std::sync::atomic::AtomicBool>) {
         use std::sync::{
             atomic::{AtomicBool, Ordering::SeqCst},
@@ -53,7 +53,7 @@ impl Connection {
         #[allow(clippy::type_complexity)]
         fn channel(
             killed: Arc<AtomicBool>,
-            executor: gpui2::Executor,
+            executor: gpui2::BackgroundExecutor,
         ) -> (
             Box<dyn Send + Unpin + futures::Sink<WebSocketMessage, Error = anyhow::Error>>,
             Box<dyn Send + Unpin + futures::Stream<Item = Result<WebSocketMessage, anyhow::Error>>>,

crates/rpc2/src/peer.rs

@@ -342,7 +342,7 @@ impl Peer {
     pub fn add_test_connection(
         self: &Arc<Self>,
         connection: Connection,
-        executor: gpui2::Executor,
+        executor: gpui2::BackgroundExecutor,
     ) -> (
         ConnectionId,
         impl Future<Output = anyhow::Result<()>> + Send,

crates/settings2/src/settings_file.rs

@@ -2,7 +2,7 @@ use crate::{settings_store::SettingsStore, Settings};
 use anyhow::Result;
 use fs2::Fs;
 use futures::{channel::mpsc, StreamExt};
-use gpui2::{AppContext, Executor};
+use gpui2::{AppContext, BackgroundExecutor};
 use std::{io::ErrorKind, path::PathBuf, str, sync::Arc, time::Duration};
 use util::{paths, ResultExt};
 
@@ -28,7 +28,7 @@ pub fn test_settings() -> String {
 }
 
 pub fn watch_config_file(
-    executor: &Executor,
+    executor: &BackgroundExecutor,
     fs: Arc<dyn Fs>,
     path: PathBuf,
 ) -> mpsc::UnboundedReceiver<String> {

crates/sqlez/src/thread_safe_connection.rs

@@ -336,13 +336,13 @@ mod test {
                         FOREIGN KEY(dock_pane) REFERENCES panes(pane_id),
                         FOREIGN KEY(active_pane) REFERENCES panes(pane_id)
                     ) STRICT;
-                    
+
                     CREATE TABLE panes(
                         pane_id INTEGER PRIMARY KEY,
                         workspace_id INTEGER NOT NULL,
                         active INTEGER NOT NULL, -- Boolean
-                        FOREIGN KEY(workspace_id) REFERENCES workspaces(workspace_id) 
+                        FOREIGN KEY(workspace_id) REFERENCES workspaces(workspace_id)
-                            ON DELETE CASCADE 
+                            ON DELETE CASCADE
                             ON UPDATE CASCADE
                     ) STRICT;
                 "]

crates/vim/src/test/vim_test_context.rs

@@ -133,9 +133,9 @@ impl<'a> VimTestContext<'a> {
     ) -> futures::channel::mpsc::UnboundedReceiver<()>
     where
         T: 'static + request::Request,
-        T::Params: 'static + Send,
+        T::Params: 'static,
-        F: 'static + Send + FnMut(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
+        F: 'static + FnMut(lsp::Url, T::Params, gpui::AsyncAppContext) -> Fut,
-        Fut: 'static + Send + Future<Output = Result<T::Result>>,
+        Fut: 'static + Future<Output = Result<T::Result>>,
     {
         self.cx.handle_request::<T, F, Fut>(handler)
     }

crates/zed2/src/main.rs

@@ -62,20 +62,26 @@ fn main() {
     log::info!("========== starting zed ==========");
     let app = App::production(Arc::new(Assets));
 
-    let installation_id = app.executor().block(installation_id()).ok();
+    let installation_id = app.background_executor().block(installation_id()).ok();
     let session_id = Uuid::new_v4().to_string();
     init_panic_hook(&app, installation_id.clone(), session_id.clone());
 
     let fs = Arc::new(RealFs);
-    let user_settings_file_rx =
+    let user_settings_file_rx = watch_config_file(
-        watch_config_file(&app.executor(), fs.clone(), paths::SETTINGS.clone());
+        &app.background_executor(),
-    let _user_keymap_file_rx =
+        fs.clone(),
-        watch_config_file(&app.executor(), fs.clone(), paths::KEYMAP.clone());
+        paths::SETTINGS.clone(),
+    );
+    let _user_keymap_file_rx = watch_config_file(
+        &app.background_executor(),
+        fs.clone(),
+        paths::KEYMAP.clone(),
+    );
 
     let login_shell_env_loaded = if stdout_is_a_pty() {
         Task::ready(())
     } else {
-        app.executor().spawn(async {
+        app.background_executor().spawn(async {
             load_login_shell_environment().await.log_err();
         })
     };