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Bug 3697

Summary: Main thread gets stuck on left mouse down
Product: SDL Reporter: Amruth Raj <amruthraj.p>
Component: videoAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: major    
Priority: P1 CC: ewasylishen
Version: HG 2.1   
Hardware: x86   
OS: Other   
Attachments: Fix
Fix exiting fullscreen desktop

Description Amruth Raj 2017-07-07 07:21:24 UTC 
- My app runs in full screen to play video(I use SDL_WINDOW_FULLSCREEN_DESKTOP)
- Cmd-tab to go out of full screen to another app
- Cmd-tab again to get back to my app
- Press left mouse button at one of the edges of the screen, don't release yet.
After this point the main thread is stuck until I release the left mouse button and hence video rendering doesn't happen anymore.

On debugging more, I see that thread 0 is stuck as shown below with sendEvent processing left mouse down. It comes out only after it receives a left mouse up. There are some frames below which show NSWindowResizing, but my window flag doesn't have SDL_WINDOW_RESIZABLE set.

Thread 0:: CrBrowserMain Dispatch queue: com.apple.main-thread
0 libsystem_kernel.dylib 0x00007fffbe13d34a mach_msg_trap + 10
1 libsystem_kernel.dylib 0x00007fffbe13c797 mach_msg + 55
2 com.apple.CoreFoundation 0x00007fffa889d434 __CFRunLoopServiceMachPort + 212
3 com.apple.CoreFoundation 0x00007fffa889c8c1 __CFRunLoopRun + 1361
4 com.apple.CoreFoundation 0x00007fffa889c114 CFRunLoopRunSpecific + 420
5 com.apple.HIToolbox 0x00007fffa7dfdebc RunCurrentEventLoopInMode + 240
6 com.apple.HIToolbox 0x00007fffa7dfdcf1 ReceiveNextEventCommon + 432
7 com.apple.HIToolbox 0x00007fffa7dfdb26 _BlockUntilNextEventMatchingListInModeWithFilter + 71
8 com.apple.AppKit 0x00007fffa6396a54 _DPSNextEvent + 1120
9 com.apple.AppKit 0x00007fffa6b127ee -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 2796
10 com.apple.AppKit 0x00007fffa66f568d +[NSWindow(NSWindowResizing) _mouseHysteresisCheck:withExpiration:andDistance:finalMouseLocation:] + 525
11 com.apple.AppKit 0x00007fffa65eedb5 -[NSWindow(NSWindowResizing) _hitTestWithHysteresisCheck:forEvent:allowWindowDragging:] + 394
12 com.apple.AppKit 0x00007fffa6c8f0db -[NSWindow(NSEventRouting) _handleMouseDownEvent:isDelayedEvent:] + 1873
13 com.apple.AppKit 0x00007fffa6c8ca6c -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 1942
14 com.apple.AppKit 0x00007fffa6c8bf0a -[NSWindow(NSEventRouting) sendEvent:] + 541
15 org.libsdl.SDL2 0x000000010d46d74a -[SDLWindow sendEvent:] + 90
16 com.apple.AppKit 0x00007fffa6b10681 -[NSApplication(NSEvent) sendEvent:] + 1145
17 org.libsdl.SDL2 0x000000010d46532b -[SDLApplication sendEvent:] + 139
18 org.libsdl.SDL2 0x000000010d466b2f Cocoa_PumpEvents + 495
19 org.libsdl.SDL2 0x000000010d44c1d5 SDL_PumpEvents_REAL + 53
20 org.libsdl.SDL2 0x000000010d44c2f5 SDL_WaitEventTimeout_REAL + 53
21 org.libsdl.SDL2 0x000000010d44c2b7 SDL_PollEvent_REAL + 23
22 org.libsdl.SDL2 0x000000010d51bb24 SDL_PollEvent + 36
23 libTest.dylib 0x000000010cf3e0e8 SDLEventProcessor::processEvents(int) + 568
24 Test 0x000000010cde6bba BrowserApp::RunAppMessageLoop(BAInstData*, CefStringBase, CefStringBase) + 810
25 Test 0x000000010ce04bbc main + 17980
26 libdyld.dylib 0x00007fffbe016235 start + 1

I further noticed that while entering full screen in SDL_cocoawindow.m NSResizableWindowMask is set. If I clear it inside windowDidEnterFullScreen, then, the issue doesn't repro.


This is discussed at https://discourse.libsdl.org/t/main-thread-gets-stuck-on-left-mouse-down/22753/3 and thanks to Eric for the pointers.
Comment 1 Amruth Raj 2017-07-07 07:23:01 UTC 
I am increasing the priority since it is a very common use case and it easily repros. Once reproduced, it makes the application stop rendering anything on screen.
Comment 2 Amruth Raj 2017-07-07 09:40:28 UTC 
Here is my patch where I verified the issue no longer occurs:

diff -r 9dda3f3e9794 src/video/cocoa/SDL_cocoawindow.m
--- a/src/video/cocoa/SDL_cocoawindow.m Wed Jul 05 12:04:37 2017 -0400
+++ b/src/video/cocoa/SDL_cocoawindow.m Fri Jul 07 15:08:16 2017 +0530
@@ -674,6 +674,7 @@
         pendingWindowOperation = PENDING_OPERATION_NONE;
         [self setFullscreenSpace:NO];
     } else {
+        SetWindowStyle(window, 0);
         if ((window->flags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP) {
             [NSMenu setMenuBarVisible:NO];
         }
Comment 3 Amruth Raj 2017-07-08 15:53:24 UTC 
Created attachment 2793 [details]
Fix
Comment 4 Sam Lantinga 2017-07-11 00:07:37 UTC 
Fixed, thanks!
https://hg.libsdl.org/SDL/rev/81e6d0f852fc
Comment 5 Eric Wasylishen 2017-07-27 19:56:53 UTC 
(In reply to Sam Lantinga from comment #4)
> Fixed, thanks!
> https://hg.libsdl.org/SDL/rev/81e6d0f852fc

Unfortunately this commit seems to have broken exiting desktop-fullscreen.
- Launch testgl2.
- Press alt+enter to go fullscreen-desktop
- Press alt+enter again. The spinning cube will freeze, and the window stays fullscreen desktop.
Comment 6 Amruth Raj 2017-07-28 10:45:25 UTC 
Problem is that the main thread gets stuck in Cocoa_SetWindowFullscreenSpace for 30 seconds while coming out of full screen.
This is happening because NSWindowWillExitFullScreenNotification fails to come after resizable: false flag is set.

I tried explicitly setting this flag before doing toggleFullscreen and a few other places, but that didn't help. I am unsure why the WillExit notification itself cannot come.
Comment 7 Eric Wasylishen 2017-08-02 03:09:25 UTC 
Created attachment 2815 [details]
Fix exiting fullscreen desktop

I think I found a better fix.

The problem with https://hg.libsdl.org/SDL/rev/81e6d0f852fc is setting the styleMask to 0 clears the NSWindowStyleMaskFullScreen bit, which then confuses Cocoa later when you try to leave fullscreen. Instead I'm just clearing the NSWindowStyleMaskResizable bit, although SetWindowStyle(window, NSWindowStyleMaskFullScreen); seems to also work.
Comment 8 Sam Lantinga 2017-08-02 03:16:27 UTC 
This is in, thanks!
https://hg.libsdl.org/SDL/rev/6709dc9adb16