gpui-pre-windows: guard the VSync `RedrawWindow` loop with `IsWindow` (spurious ERROR_INVALID_WINDOW_HANDLE on window close)

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
77/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
rust
Domain
desktop

Research direction

Read src/platform.rs and inspect begin_vsync_thread, especially the loop over all_windows and its RedrawWindow call. Check how WindowsWindow::drop and WM_GPUI_CLOSE_ONE_WINDOW affect the lifetime of those handles. Add the described guard for invalid HWNDs, then confirm closing a secondary window no longer logs the error.

Written by the indexing model from the issue text.

Description

What happens

Closing a secondary GPUI window on Windows logs a spurious COM error once per frame, for a tick or two after the window is gone:

ERROR 无效的窗口句柄。 (0x80070578)      // ERROR_INVALID_WINDOW_HANDLE

It comes from the VSync thread calling RedrawWindow on an already destroyed HWND. Every close of a settings/dialog window in our app prints it, so it looks like the app is broken even though nothing is.

Why

gpui-pre-windows' begin_vsync_thread (src/platform.rs, zed's crates/gpui_windows/src/platform.rs) redraws every handle tracked in all_windows:

for hwnd in all_windows.read().iter() {
    unsafe {
        if let Some(signal_at) = signal_at {
            if IsWindowVisible(hwnd.as_raw()).as_bool() && !IsIconic(hwnd.as_raw()).as_bool() {
                ...
            }
        }
        RedrawWindow(Some(hwnd.as_raw()), None, None, RDW_INVALIDATE)
            .ok()
            .log_err();
    }
}

The handle is destroyed by WindowsWindow::drop → DestroyWindow, but its entry in the raw-handle list is pruned only when the WM_GPUI_CLOSE_ONE_WINDOW message that DestroyWindow posts gets processed. Between those two points the VSync thread still sees the destroyed handle, and RedrawWindow fails with ERROR_INVALID_WINDOW_HANDLE (which is then log_err'd at ERROR level).

IsWindowVisible does not help: it returns false for an invalid handle, but the RedrawWindow call is unconditional, so it is reached either way.

Fix

Skip stale handles in the VSync loop:

for hwnd in all_windows.read().iter() {
    unsafe {
        // The HWND outlives its GPUI entry for a tick or two: the raw handle is
        // pruned only after WM_DESTROY is processed. RedrawWindow on a destroyed
        // handle logs a spurious ERROR_INVALID_WINDOW_HANDLE; skip it.
        if !IsWindow(Some(hwnd.as_raw())).as_bool() {
            continue;
        }
        ...

A more thorough fix would be to remove the handle from all_windows in WindowsWindow::drop (or in the DestroyWindow path) so the VSync thread never sees a stale handle at all; the IsWindow check above is the minimal, allocation-free version we have been carrying.

Notes
  • Verified against gpui-pre-windows 0.3.10 and 0.3.11 (zed f816e1f). The same loop in zed main (crates/gpui_windows/src/platform.rs) is still unguarded, so this may be worth a PR upstream as well.
  • IsWindow is already in scope there (UI::WindowsAndMessaging::*), windows 0.62 signature: IsWindow(Some(hwnd.as_raw())).as_bool().
  • We vendor gpui-pre-windows with this one-line guard (diff and repro notes in https://github.com/qiuzhanghua/qcode/blob/main/vendor/gpui-pre-windows/README.qcode.md); once this is fixed upstream we can drop the fork.
Dominant language
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