ui: Fix hanging up Cocoa display on macOS 10.15 (Catalina)

macOS API documentation says that before applicationDidFinishLaunching is called, any events will not be processed. However, some events are fired before it is called in macOS Catalina. This causes deadlock of iothread_lock in handleEvent while it will be released after the app_started_sem is posted. This patch avoids processing events before the app_started_sem is posted to prevent this deadlock. Buglink: https://bugs.launchpad.net/qemu/+bug/1847906 Signed-off-by: Hikaru Nishida <[email protected]> Message-id: [email protected] Signed-off-by: Gerd Hoffmann <[email protected]>
tanyav2 · Oct 18, 2019 · dff742a · dff742a
1 parent f22f553
commit dff742a
Showing 1 changed file with 12 additions and 0 deletions.
diff --git a/ui/cocoa.m b/ui/cocoa.m
@@ -134,6 +134,7 @@
 
 static QemuSemaphore display_init_sem;
 static QemuSemaphore app_started_sem;
+static bool allow_events;
 
 // Utility functions to run specified code block with iothread lock held
 typedef void (^CodeBlock)(void);
@@ -729,6 +730,16 @@ - (void) handleMonitorInput:(NSEvent *)event
 
 - (bool) handleEvent:(NSEvent *)event
 {
+    if(!allow_events) {
+        /*
+         * Just let OSX have all events that arrive before
+         * applicationDidFinishLaunching.
+         * This avoids a deadlock on the iothread lock, which cocoa_display_init()
+         * will not drop until after the app_started_sem is posted. (In theory
+         * there should not be any such events, but OSX Catalina now emits some.)
+         */
+        return false;
+    }
     return bool_with_iothread_lock(^{
         return [self handleEventLocked:event];
     });
@@ -1156,6 +1167,7 @@ - (void) dealloc
 - (void)applicationDidFinishLaunching: (NSNotification *) note
 {
     COCOA_DEBUG("QemuCocoaAppController: applicationDidFinishLaunching\n");
+    allow_events = true;
     /* Tell cocoa_display_init to proceed */
     qemu_sem_post(&app_started_sem);
 }