WIP

crates/gpui2/src/executor.rs

@@ -1,7 +1,10 @@
 use crate::{AppContext, PlatformDispatcher};
+use futures::channel::mpsc;
 use smol::prelude::*;
 use std::{
     fmt::Debug,
+    marker::PhantomData,
+    mem,
     pin::Pin,
     sync::Arc,
     task::{Context, Poll},
@@ -133,7 +136,73 @@ impl Executor {
         futures::executor::block_on(future)
     }
 
+    pub async fn scoped<'scope, F>(&self, scheduler: F)
+    where
+        F: FnOnce(&mut Scope<'scope>),
+    {
+        let mut scope = Scope::new(self.clone());
+        (scheduler)(&mut scope);
+        let spawned = mem::take(&mut scope.futures)
+            .into_iter()
+            .map(|f| self.spawn(f))
+            .collect::<Vec<_>>();
+        for task in spawned {
+            task.await;
+        }
+    }
+
     pub fn is_main_thread(&self) -> bool {
         self.dispatcher.is_main_thread()
     }
 }
+
+pub struct Scope<'a> {
+    executor: Executor,
+    futures: Vec<Pin<Box<dyn Future<Output = ()> + Send + 'static>>>,
+    tx: Option<mpsc::Sender<()>>,
+    rx: mpsc::Receiver<()>,
+    lifetime: PhantomData<&'a ()>,
+}
+
+impl<'a> Scope<'a> {
+    fn new(executor: Executor) -> Self {
+        let (tx, rx) = mpsc::channel(1);
+        Self {
+            executor,
+            tx: Some(tx),
+            rx,
+            futures: Default::default(),
+            lifetime: PhantomData,
+        }
+    }
+
+    pub fn spawn<F>(&mut self, f: F)
+    where
+        F: Future<Output = ()> + Send + 'a,
+    {
+        let tx = self.tx.clone().unwrap();
+
+        // Safety: The 'a lifetime is guaranteed to outlive any of these futures because
+        // dropping this `Scope` blocks until all of the futures have resolved.
+        let f = unsafe {
+            mem::transmute::<
+                Pin<Box<dyn Future<Output = ()> + Send + 'a>>,
+                Pin<Box<dyn Future<Output = ()> + Send + 'static>>,
+            >(Box::pin(async move {
+                f.await;
+                drop(tx);
+            }))
+        };
+        self.futures.push(f);
+    }
+}
+
+impl<'a> Drop for Scope<'a> {
+    fn drop(&mut self) {
+        self.tx.take().unwrap();
+
+        // Wait until the channel is closed, which means that all of the spawned
+        // futures have resolved.
+        self.executor.block(self.rx.next());
+    }
+}