Question

我在我的应用中有这个代码：

[[self assetsLibrary] assetForURL:info.media.url resultBlock:^(ALAsset *asset) {
    ALAssetRepresentation *rep = [asset defaultRepresentation];
    CGImageRef img = [rep fullScreenImage];
    photoLayer.contents =  img;
} failureBlock:^(NSError *error) {

}];

代码到达填充img变量的行并停在那里，应用程序锁定没有错误。 NSLog回声大小，所以我知道资产就在那里。我不知道如何解决这个问题，它以前工作过，但刚刚停止了！有没有人在这里看到任何不合适的东西？

以下是网址的内容：

assets-library://asset/asset.JPG?id=36E68169-7BB4-48D7-B8E1-244234C9F1DA&ext=JPG

冻结时堆栈跟踪：

Thread 1, Queue : NSManagedObjectContext Queue
#0  0x37b1af38 in syscall_thread_switch ()
#1  0x331a5978 in OSSpinLockLock$VARIANT$wfe ()
#2  0x3318bcae in pthread_once ()
#3  0x348f66e2 in _internalCheckSupportsDCTDownScaling ()
#4  0x348f63fa in _initalizeService ()
#5  0x3318bcde in pthread_once ()
#6  0x348f63ba in jpegService ()
#7  0x3497009c in FigCreateCGImageFromJPEG ()
#8  0x356b5728 in PLCreateImageFromDataWithFormat ()
#9  0x35a3205e in __block_global_0 ()
#10 0x356a03f4 in -[PLAssetsSaver requestSynchronousImageFromAsset:withFormat:completionBlock:] ()
#11 0x35a32028 in __40-[ALAssetRepresentation fullScreenImage]_block_invoke_0 ()
#12 0x35a387ec in __53-[ALAssetRepresentationPrivate _performBlockAndWait:]_block_invoke_0 ()
#13 0x328e79a0 in developerSubmittedBlockToNSManagedObjectContextPerform ()
#14 0x3121c5da in _dispatch_client_callout ()
#15 0x3121f80e in _dispatch_barrier_sync_f_invoke ()
#16 0x328e7b22 in -[NSManagedObjectContext performBlockAndWait:] ()
#17 0x35a351b2 in -[ALAssetsLibrary _performBlockAndWait:] ()
#18 0x35a385ac in -[ALAssetRepresentationPrivate _performBlockAndWait:] ()
#19 0x35a31f24 in -[ALAssetRepresentation fullScreenImage] ()
#20 0x0008a3ca in __31-[MasterTimeLine getPhotoItem:]_block_invoke_0 at /Users/jasoncandelora/Desktop/Glance/iOS/projects/VideoBuilderTest1/VideoBuilderTest1/MasterTimeLine.m:789
#21 0x35a371b2 in __block_global_14 ()
#22 0x3121c792 in _dispatch_call_block_and_release ()
#23 0x3121c5da in _dispatch_client_callout ()
#24 0x3121fe44 in _dispatch_main_queue_callback_4CF ()
#25 0x357ff1b0 in __CFRunLoopRun ()
#26 0x3577223c in CFRunLoopRunSpecific ()
#27 0x357720c8 in CFRunLoopRunInMode ()
#28 0x3702133a in GSEventRunModal ()
#29 0x340ec290 in UIApplicationMain ()
#30 0x0006eda4 in main at /Users/jasoncandelora/Desktop/Glance/iOS/projects/VideoBuilderTest1/VideoBuilderTest1/main.m:16


Thread 3, Queue : com.apple.libdispatch-manager
#0  0x37b1b5d0 in kevent64 ()
#1  0x31221d26 in _dispatch_mgr_invoke ()
#2  0x3121d378 in _dispatch_mgr_thread ()



Thread 5 WebThread, Queue : (null)
#0  0x37b1ae30 in mach_msg_trap ()
#1  0x37b1afd4 in mach_msg ()
#2  0x358002ba in __CFRunLoopServiceMachPort ()
#3  0x357ff030 in __CFRunLoopRun ()
#4  0x3577223c in CFRunLoopRunSpecific ()
#5  0x357720c8 in CFRunLoopRunInMode ()
#6  0x3376ea5c in RunWebThread(void*) ()
#7  0x331950e0 in _pthread_start ()
#8  0x33194fa8 in thread_start ()


Thread 8 com.apple.coremedia.player.async, Queue : (null)
#0  0x37b2b08c in __psynch_cvwait ()
#1  0x3318db00 in _pthread_cond_wait ()
#2  0x33197cfc in pthread_cond_wait ()
#3  0x336ef8b8 in FigSemaphoreWaitRelative ()
#4  0x39b30eae in fpa_AsyncMovieControlThread ()
#5  0x3370d97a in figThreadMain ()
#6  0x331950e0 in _pthread_start ()
#7  0x33194fa8 in thread_start ()





Thread 9 com.apple.coremedia.player.remote, Queue : (null)
#0  0x37b1ae30 in mach_msg_trap ()
#1  0x37b1afd4 in mach_msg ()
#2  0x39b370d8 in FigExpressNotificationThread ()
#3  0x3370d97a in figThreadMain ()
#4  0x331950e0 in _pthread_start ()
#5  0x33194fa8 in thread_start ()

Answer 1

您不应该使用这种技巧来尝试强制异步资产检索操作进入同步操作。最有可能的原因是死锁，检查各种线程的堆栈跟踪，你可能会看到多个线程正在等待信号量。

我建议您删除信号量锁定内容并让操作异步。

另一个建议：您是否确保用户实际允许访问照片（iOS6上的新隐私设置）？

关于您发布的堆栈输出：

我看到了一个FigSemaphoreWaitRelative和OSSpinLockLock $ VARIANT $ wfe。第一个是等待信号量被解锁。后者是另一种形式的锁定，而系统显然会检查您尝试访问的媒体是否可以在硬件中解码（_internalCheckSupportsDCTDownScaling）。

由于某种原因，此操作不仅会卡住，而且还会阻塞主线程，即线程1.您是否打开了一个媒体播放器视图（com.apple.coremedia.player.async）阻止视频硬件和这可以防止上面的DCTDownScaling检查死锁？

长话短说：听起来你应该为此提交雷达，对我来说看起来像是一个iOS错误。

Answer 2

尝试将最后一行代码移至主队列：

[[self assetsLibrary] assetForURL:info.media.url resultBlock:^(ALAsset *asset) {
    ALAssetRepresentation *rep = [asset defaultRepresentation];
    CGImageRef img = [rep fullScreenImage];
    dispatch_async(dispatch_get_main_queue(), ^{
        photoLayer.contents =  img;
    };
} failureBlock:^(NSError *error) {

}];

如果这不起作用，这有多大的资产？

Answer 3

在我的情况下，我重启了设备，现在正在运行。谢谢你的帮助

从AlAsset获取图像会破坏我的应用程序

3 个答案: