From aa899f6d785826446f105c18f94e863f8c2e2b94 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukas@zed.dev>
Date: Thu, 27 Nov 2025 18:14:42 +0100
Subject: [PATCH] gpui: Give windows message loop processing chances when we
 overload the main thread with tasks (#43678)

This reduces hangs on windows when we have many tasks queued up on the
main thread that yield a lot.

Release Notes:

- Reduced hangs on windows in some situations
---
 .../gpui/src/platform/windows/dispatcher.rs   |  2 +-
 crates/gpui/src/platform/windows/platform.rs  | 23 +++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/crates/gpui/src/platform/windows/dispatcher.rs b/crates/gpui/src/platform/windows/dispatcher.rs
index f543202e77c75acfd007d632b2023317dcba43b6..dd53c86f5ed687c9b22a08779f262392f44a66ce 100644
--- a/crates/gpui/src/platform/windows/dispatcher.rs
+++ b/crates/gpui/src/platform/windows/dispatcher.rs
@@ -25,7 +25,7 @@ pub(crate) struct WindowsDispatcher {
     pub(crate) wake_posted: AtomicBool,
     main_sender: Sender<RunnableVariant>,
     main_thread_id: ThreadId,
-    platform_window_handle: SafeHwnd,
+    pub(crate) platform_window_handle: SafeHwnd,
     validation_number: usize,
 }
 
diff --git a/crates/gpui/src/platform/windows/platform.rs b/crates/gpui/src/platform/windows/platform.rs
index 942cb62d2216c8d7cd5ea4cf75c4e4fa4a7d007f..548b08eca8f254825bc5a42bf74089c0f230c4ac 100644
--- a/crates/gpui/src/platform/windows/platform.rs
+++ b/crates/gpui/src/platform/windows/platform.rs
@@ -813,9 +813,28 @@ impl WindowsPlatformInner {
 
     #[inline]
     fn run_foreground_task(&self) -> Option<isize> {
+        const MAIN_TASK_TIMEOUT: u128 = 10;
+
+        let start = std::time::Instant::now();
         loop {
-            for runnable in self.main_receiver.drain() {
-                WindowsDispatcher::execute_runnable(runnable);
+            loop {
+                if start.elapsed().as_millis() >= MAIN_TASK_TIMEOUT {
+                    // requeue main thread dispatch and bail, allowing more system messages to be processed
+                    unsafe {
+                        PostMessageW(
+                            Some(self.dispatcher.platform_window_handle.as_raw()),
+                            WM_GPUI_TASK_DISPATCHED_ON_MAIN_THREAD,
+                            WPARAM(self.validation_number),
+                            LPARAM(0),
+                        )
+                        .log_err();
+                    }
+                    return Some(0);
+                }
+                match self.main_receiver.try_recv() {
+                    Err(_) => break,
+                    Ok(runnable) => WindowsDispatcher::execute_runnable(runnable),
+                }
             }
 
             // Someone could enqueue a Runnable here. The flag is still true, so they will not PostMessage.