Los métodos de UIStringDrawing no parecen ser seguros para subprocesos en iOS 6
El uso de cualquier método UIStringDrawing en dos subprocesos provoca simultáneamente un bloqueo. Mi entendimiento fue que todos los métodos de UIStringDrawing estaban a salvo de iOS 4.0.
Este código (que no hace nada de ningún uso) demuestra el problema:
dispatch_queue_t queue = dispatch_queue_create("com.queue", NULL);
for (int i = 0; i < 10000; i++) {
dispatch_async(queue, ^{
NSString *string = @"My string";
CGSize size = [string sizeWithFont:[UIFont boldSystemFontOfSize:13]];
});
}
for (int i = 0; i < 10000; i++) {
NSString *string = @"My string";
CGSize size = [string sizeWithFont:[UIFont boldSystemFontOfSize:13]];
}
dispatch_release(queue);
La aplicación se bloquea después de algunas iteraciones de los bucles con el siguiente retroceso:
* thread #1: tid = 0x2403, 0x00ad40c8, stop reason = EXC_BAD_ACCESS (code=2, address=0xad40c8)
frame #0: 0x00ad40c8
frame #1: 0x36bc4252 WebCore`WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 90
frame #2: 0x36bc41f2 WebCore`WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 10
frame #3: 0x38f0368e WebKit`rendererForFont(__GSFont*) + 246
frame #4: 0x38f03230 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:forWidth:ellipsis:letterSpacing:resultRange:] + 200
frame #5: 0x38f03162 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:forWidth:ellipsis:letterSpacing:] + 66
frame #6: 0x38f04532 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:] + 58
frame #7: 0x361dc5d2 UIKit`-[NSString(UIStringDrawing) sizeWithFont:] + 46
frame #8: 0x00060ca8 myApp`-[TAViewController drawingTest] + 216 at TAViewController.m:157
frame #9: 0x38da1e66 Foundation`__NSFireDelayedPerform + 450
frame #10: 0x3aa47856 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 14
frame #11: 0x3aa47502 CoreFoundation`__CFRunLoopDoTimer + 274
frame #12: 0x3aa46176 CoreFoundation`__CFRunLoopRun + 1230
frame #13: 0x3a9b923c CoreFoundation`CFRunLoopRunSpecific + 356
frame #14: 0x3a9b90c8 CoreFoundation`CFRunLoopRunInMode + 104
frame #15: 0x3a8a433a GraphicsServices`GSEventRunModal + 74
frame #16: 0x3622c288 UIKit`UIApplicationMain + 1120
frame #17: 0x0005f08c myApp`main + 96 at main.m:16
thread #5: tid = 0x2a03, 0x00ad40c8, stop reason = EXC_BAD_ACCESS (code=2, address=0xad40c8)
frame #0: 0x00ad40c8
frame #1: 0x36bc4252 WebCore`WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 90
frame #2: 0x36bc41f2 WebCore`WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 10
frame #3: 0x38f0368e WebKit`rendererForFont(__GSFont*) + 246
frame #4: 0x38f03230 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:forWidth:ellipsis:letterSpacing:resultRange:] + 200
frame #5: 0x38f03162 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:forWidth:ellipsis:letterSpacing:] + 66
frame #6: 0x38f04532 WebKit`-[NSString(WebStringDrawing) _web_sizeWithFont:] + 58
frame #7: 0x361dc5d2 UIKit`-[NSString(UIStringDrawing) sizeWithFont:] + 46
frame #8: 0x00060d5c myApp`__31-[TAViewController drawingTest]_block_invoke_0 + 116 at TAViewController.m:150
frame #9: 0x339f0792 libdispatch.dylib`_dispatch_call_block_and_release + 10
frame #10: 0x339f3b3a libdispatch.dylib`_dispatch_queue_drain + 142
frame #11: 0x339f167c libdispatch.dylib`_dispatch_queue_invoke + 44
frame #12: 0x339f4612 libdispatch.dylib`_dispatch_root_queue_drain + 210
frame #13: 0x339f47d8 libdispatch.dylib`_dispatch_worker_thread2 + 92
frame #14: 0x37f957f0 libsystem_c.dylib`_pthread_wqthread + 360
frame #15: 0x37f95684 libsystem_c.dylib`start_wqthread + 8
Mi entendimiento fue que los métodos de UIStringDrawing eran seguros para subprocesos desde iOS 4. Espero que estos bucles se completen sin errores.
El bloqueo ocurre cuando se ejecuta en un iPhone con iOS 6 (probado en iPhone 5) pero NO ocurre cuando se ejecuta en un iPhone con iOS 5 (probado en iPhone 4) o en el simulador (probado con iOS 6).
He implementado lo que pensé que era una solución al serializar las llamadas de sorteo usando CGD:
- (void)serialiseDrawing:(void (^)())block {
dispatch_sync(self.serialDrawingQueue, block);
}
- (dispatch_queue_t)serialDrawingQueue {
if (_serialDrawingQueue == NULL) _serialDrawingQueue = dispatch_queue_create("com.myApp.SerialDrawQueue", NULL);
return _serialDrawingQueue;
}
... y envolviendo cada sorteo de esta manera:
__block CGSize labelSize = CGSizeZero;
[[TAUtils sharedUtils] serialiseDrawing:^{
labelSize = [label.text sizeWithFont:label.font];
}];
Esto parece haber mejorado un poco las cosas (todas mis llamadas de UIStringDrawing ocurren en un hilo). Pero todavía se estrellará a veces con un retroceso como este:
Exception Type: EXC_CRASH (SIGSEGV)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Crashed Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0 libsystem_kernel.dylib 0x3a28ee80 semaphore_wait_trap + 8
1 libdispatch.dylib 0x32851e90 _dispatch_thread_semaphore_wait + 8
2 libdispatch.dylib 0x32850680 _dispatch_barrier_sync_f_slow + 100
3 myApp 0x000c4330 -[TAUtils serialiseDrawing:] (TAUtils.m:305)
4 myApp 0x000edfd4 -[TAOmniBar updateLabel] (TAOmniBar.m:394)
5 myApp 0x000ee8d6 -[TAOmniBar handleNotification:] (TAOmniBar.m:461)
6 CoreFoundation 0x39820346 _CFXNotificationPost + 1418
7 Foundation 0x37b5838a -[NSNotificationCenter postNotificationName:object:userInfo:] + 66
8 Foundation 0x37b5be9a -[NSNotificationCenter postNotificationName:object:] + 26
9 myApp 0x000f369a -[TAMyViewController update] (TAMyViewController.m:1308)
10 GLKit 0x328383ce -[GLKViewController _updateAndDraw] + 270
11 QuartzCore 0x39ffd77c CA::Display::DisplayLink::dispatch(unsigned long long, unsigned long long) + 156
12 QuartzCore 0x39ffd6d4 CA::Display::IOMFBDisplayLink::callback(__IOMobileFramebuffer*, unsigned long long, unsigned long long, unsigned long long, void*) + 60
13 IOMobileFramebuffer 0x31221fd4 IOMobileFramebufferVsyncNotifyFunc + 152
14 IOKit 0x39f7c5aa IODispatchCalloutFromCFMessage + 190
15 CoreFoundation 0x39899888 __CFMachPortPerform + 116
16 CoreFoundation 0x398a43e4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 32
17 CoreFoundation 0x398a4386 __CFRunLoopDoSource1 + 134
18 CoreFoundation 0x398a320a __CFRunLoopRun + 1378
19 CoreFoundation 0x39816238 CFRunLoopRunSpecific + 352
20 CoreFoundation 0x398160c4 CFRunLoopRunInMode + 100
21 GraphicsServices 0x39701336 GSEventRunModal + 70
22 UIKit 0x35089284 UIApplicationMain + 1116
23 myApp 0x000b806e main (main.m:16)
24 myApp 0x000b8024 start + 36
Thread 7 name: Dispatch queue: com.myApp.SerialDrawQueue
Thread 7:
0 WebCore 0x35a21410 WebCore::FontFallbackList::invalidate(WTF::PassRefPtr<WebCore::FontSelector>) + 156
1 WebCore 0x35a2124e WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 86
2 WebCore 0x35a211ee WebCore::Font::Font(WebCore::FontPlatformData const&, WTF::PassRefPtr<WebCore::FontSelector>) + 6
3 WebKit 0x37d6068a rendererForFont(__GSFont*) + 242
4 WebKit 0x37d61796 -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:renderedStringOut:drawUnderline:] + 198
5 WebKit 0x37d616bc -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:renderedStringOut:] + 84
6 WebKit 0x37d6165e -[NSString(WebStringDrawing) __web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:measureOnly:] + 82
7 WebKit 0x37d61602 -[NSString(WebStringDrawing) _web_drawAtPoint:forWidth:withFont:ellipsis:letterSpacing:includeEmoji:] + 78
8 UIKit 0x35041960 -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:lineBreakMode:letterSpacing:includeEmoji:] + 172
9 UIKit 0x3507de1e -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:fontSize:lineBreakMode:baselineAdjustment:includeEmoji:] + 358
10 UIKit 0x3507dca4 -[NSString(UIStringDrawing) drawAtPoint:forWidth:withFont:fontSize:lineBreakMode:baselineAdjustment:] + 68
11 myApp 0x000d3300 -[TALabelManager textureCGImageForString:] (TALabelManager.m:859)
12 myApp 0x000d350a __39-[TALabelManager textureDataForString:]_block_invoke_0 (TALabelManager.m:875)
13 libdispatch.dylib 0x3284d5d8 _dispatch_client_callout + 20
14 libdispatch.dylib 0x3285080a _dispatch_barrier_sync_f_invoke + 22
15 myApp 0x000c4330 -[TAUtils serialiseDrawing:] (TAUtils.m:305)
16 myApp 0x000d3420 -[TALabelManager textureDataForString:] (TALabelManager.m:873)
17 myApp 0x000d0dde __block_global_0 (TALabelManager.m:516)
18 libdispatch.dylib 0x3284d790 _dispatch_call_block_and_release + 8
19 libdispatch.dylib 0x32850b36 _dispatch_queue_drain + 138
20 libdispatch.dylib 0x3284e678 _dispatch_queue_invoke + 40
21 libdispatch.dylib 0x32851610 _dispatch_root_queue_drain + 208
22 libdispatch.dylib 0x328517d4 _dispatch_worker_thread2 + 88
23 libsystem_c.dylib 0x36df27ee _pthread_wqthread + 358
24 libsystem_c.dylib 0x36df2680 start_wqthread + 4
Pido disculpas por la larga pregunta, pero este es un problema grave para mí y realmente agradecería cualquier ayuda.