Fixed rare crash trying to interrupt SDL_WaitEvent()

Fixes #12797

Author: slouken

src/events/SDL_events.c

@@ -1102,16 +1102,11 @@ static void SDL_SendWakeupEvent(void)
         return;
     }
 
-    SDL_LockMutex(_this->wakeup_lock);
-    {
-        if (_this->wakeup_window) {
-            _this->SendWakeupEvent(_this, _this->wakeup_window);
-
-            // No more wakeup events needed until we enter a new wait
-            _this->wakeup_window = NULL;
-        }
+    // We only want to do this once while waiting for an event, so set it to NULL atomically here
+    SDL_Window *wakeup_window = (SDL_Window *)SDL_SetAtomicPointer(&_this->wakeup_window, NULL);
+    if (wakeup_window) {
+        _this->SendWakeupEvent(_this, wakeup_window);
     }
-    SDL_UnlockMutex(_this->wakeup_lock);
 #endif
 }
 
@@ -1549,18 +1544,7 @@ static int SDL_WaitEventTimeout_Device(SDL_VideoDevice *_this, SDL_Window *wakeu
         */
         SDL_PumpEventsInternal(true);
 
-        SDL_LockMutex(_this->wakeup_lock);
-        {
-            status = SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_EVENT_FIRST, SDL_EVENT_LAST);
-            // If status == 0 we are going to block so wakeup will be needed.
-            if (status == 0) {
-                _this->wakeup_window = wakeup_window;
-            } else {
-                _this->wakeup_window = NULL;
-            }
-        }
-        SDL_UnlockMutex(_this->wakeup_lock);
-
+        status = SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_EVENT_FIRST, SDL_EVENT_LAST);
         if (status < 0) {
             // Got an error: return
             break;
@@ -1573,8 +1557,6 @@ static int SDL_WaitEventTimeout_Device(SDL_VideoDevice *_this, SDL_Window *wakeu
         if (timeoutNS > 0) {
             Sint64 elapsed = SDL_GetTicksNS() - start;
             if (elapsed >= timeoutNS) {
-                // Set wakeup_window to NULL without holding the lock.
-                _this->wakeup_window = NULL;
                 return 0;
             }
             loop_timeoutNS = (timeoutNS - elapsed);
@@ -1587,9 +1569,9 @@ static int SDL_WaitEventTimeout_Device(SDL_VideoDevice *_this, SDL_Window *wakeu
                 loop_timeoutNS = poll_intervalNS;
             }
         }
+        SDL_SetAtomicPointer(&_this->wakeup_window, wakeup_window);
         status = _this->WaitEventTimeout(_this, loop_timeoutNS);
-        // Set wakeup_window to NULL without holding the lock.
-        _this->wakeup_window = NULL;
+        SDL_SetAtomicPointer(&_this->wakeup_window, NULL);
         if (status == 0 && poll_intervalNS != SDL_MAX_SINT64 && loop_timeoutNS == poll_intervalNS) {
             // We may have woken up to poll. Try again
             continue;

src/video/SDL_sysvideo.h

@@ -405,8 +405,7 @@ struct SDL_VideoDevice
     bool checked_texture_framebuffer;
     bool is_dummy;
     bool suspend_screensaver;
-    SDL_Window *wakeup_window;
-    SDL_Mutex *wakeup_lock; // Initialized only if WaitEventTimeout/SendWakeupEvent are supported
+    void *wakeup_window;
     int num_displays;
     SDL_VideoDisplay **displays;
     SDL_Rect desktop_bounds;

src/video/SDL_video.c

@@ -4393,9 +4393,7 @@ void SDL_DestroyWindow(SDL_Window *window)
         _this->current_glwin = NULL;
     }
 
-    if (_this->wakeup_window == window) {
-        _this->wakeup_window = NULL;
-    }
+    SDL_CompareAndSwapAtomicPointer(&_this->wakeup_window, window, NULL);
 
     // Now invalidate magic
     SDL_SetObjectValid(window, SDL_OBJECT_TYPE_WINDOW, false);

src/video/cocoa/SDL_cocoavideo.m

@@ -49,9 +49,6 @@ @implementation SDL_CocoaVideoData
 static void Cocoa_DeleteDevice(SDL_VideoDevice *device)
 {
     @autoreleasepool {
-        if (device->wakeup_lock) {
-            SDL_DestroyMutex(device->wakeup_lock);
-        }
         CFBridgingRelease(device->internal);
         SDL_free(device);
     }
@@ -81,7 +78,6 @@ static void Cocoa_DeleteDevice(SDL_VideoDevice *device)
             return NULL;
         }
         device->internal = (SDL_VideoData *)CFBridgingRetain(data);
-        device->wakeup_lock = SDL_CreateMutex();
         device->system_theme = Cocoa_GetSystemTheme();
 
         // Set the function pointers

src/video/wayland/SDL_waylandvideo.c

@@ -447,9 +447,6 @@ static void Wayland_DeleteDevice(SDL_VideoDevice *device)
         WAYLAND_wl_display_disconnect(data->display);
         SDL_ClearProperty(SDL_GetGlobalProperties(), SDL_PROP_GLOBAL_VIDEO_WAYLAND_WL_DISPLAY_POINTER);
     }
-    if (device->wakeup_lock) {
-        SDL_DestroyMutex(device->wakeup_lock);
-    }
     SDL_free(data);
     SDL_free(device);
     SDL_WAYLAND_UnloadSymbols();
@@ -576,7 +573,6 @@ static SDL_VideoDevice *Wayland_CreateDevice(bool require_preferred_protocols)
     }
 
     device->internal = data;
-    device->wakeup_lock = SDL_CreateMutex();
 
     // Set the function pointers
     device->VideoInit = Wayland_VideoInit;

src/video/windows/SDL_windowsvideo.c

@@ -124,9 +124,6 @@ static void WIN_DeleteDevice(SDL_VideoDevice *device)
         SDL_UnloadObject(data->dxgiDLL);
     }
 #endif
-    if (device->wakeup_lock) {
-        SDL_DestroyMutex(device->wakeup_lock);
-    }
     SDL_free(device->internal->rawinput);
     SDL_free(device->internal);
     SDL_free(device);
@@ -152,7 +149,6 @@ static SDL_VideoDevice *WIN_CreateDevice(void)
         return NULL;
     }
     device->internal = data;
-    device->wakeup_lock = SDL_CreateMutex();
     device->system_theme = WIN_GetSystemTheme();
 
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)

src/video/x11/SDL_x11video.c

@@ -65,9 +65,6 @@ static void X11_DeleteDevice(SDL_VideoDevice *device)
         X11_XCloseDisplay(data->request_display);
     }
     SDL_free(data->windowlist);
-    if (device->wakeup_lock) {
-        SDL_DestroyMutex(device->wakeup_lock);
-    }
     SDL_free(device->internal);
     SDL_free(device);
 
@@ -148,8 +145,6 @@ static SDL_VideoDevice *X11_CreateDevice(void)
         return NULL;
     }
 
-    device->wakeup_lock = SDL_CreateMutex();
-
 #ifdef X11_DEBUG
     X11_XSynchronize(data->display, True);
 #endif