Suspend macOS threads during crashes (#36520)

This should improve our detection of which thread crashed since they
wont be able to resume while the minidump is being generated.

Release Notes:

- N/A

crates/crashes/Cargo.toml

@@ -16,6 +16,9 @@ serde.workspace = true
 serde_json.workspace = true
 workspace-hack.workspace = true
 
+[target.'cfg(target_os = "macos")'.dependencies]
+mach2.workspace = true
+
 [lints]
 workspace = true
 

crates/crashes/src/crashes.rs

@@ -74,6 +74,9 @@ pub async fn init(crash_init: InitCrashHandler) {
                 .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
                 .is_ok()
             {
+                #[cfg(target_os = "macos")]
+                suspend_all_other_threads();
+
                 client.ping().unwrap();
                 client.request_dump(crash_context).is_ok()
             } else {
@@ -98,6 +101,23 @@ pub async fn init(crash_init: InitCrashHandler) {
     }
 }
 
+#[cfg(target_os = "macos")]
+unsafe fn suspend_all_other_threads() {
+    let task = unsafe { mach2::traps::current_task() };
+    let mut threads: mach2::mach_types::thread_act_array_t = std::ptr::null_mut();
+    let mut count = 0;
+    unsafe {
+        mach2::task::task_threads(task, &raw mut threads, &raw mut count);
+    }
+    let current = unsafe { mach2::mach_init::mach_thread_self() };
+    for i in 0..count {
+        let t = unsafe { *threads.add(i as usize) };
+        if t != current {
+            unsafe { mach2::thread_act::thread_suspend(t) };
+        }
+    }
+}
+
 pub struct CrashServer {
     initialization_params: OnceLock<InitCrashHandler>,
     panic_info: OnceLock<CrashPanic>,