ios - 当应用程序进入前台时 Webthread 锁定主线程

Question

我正在使用 UIWebView 在我的 iOS 应用程序中嵌入 YouTube HTML 播放器，有时当应用程序从后台进入前台(并且正在播放视频)时，应用程序刚刚卡住，我遇到了 0x000000008badf00d 崩溃。

OS Version:          iOS 7.1.1 (11D201)
Report Version:      104

Exception Type:  00000020
Exception Codes: 0x000000008badf00d
Highlighted Thread:  0

Application Specific Information:
com.myapp.myapp failed to resume in time

Elapsed total CPU time (seconds): 6.460 (user 6.460, system 0.000), 27% CPU 
Elapsed application CPU time (seconds): 3.069, 13% CPU

Thread 0:
0   libsystem_kernel.dylib          0x39911f9c __psynch_mutexwait + 24
1   libsystem_pthread.dylib         0x3997b298 _pthread_mutex_lock_contended + 48
2   libsystem_pthread.dylib         0x39977d36 _pthread_mutex_lock + 258
3   WebCore                         0x36e2f190 _WebTryThreadLock(bool) + 40
4   WebCore                         0x36e2ffb8 WebThreadLock + 76
5   WebCore                         0x36e6b962 -[TileLayer layoutSublayers] + 14
6   QuartzCore                      0x3106db3a CA::Layer::layout_if_needed(CA::Transaction*) + 346
7   QuartzCore                      0x3106d9cc CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 12
8   QuartzCore                      0x3106d3e0 CA::Context::commit_transaction(CA::Transaction*) + 224
9   QuartzCore                      0x3106d1f2 CA::Transaction::commit() + 310
10  AVFoundation                    0x2da4fb60 -[AVPlayerLayer _updateSubtitles:forceRender:] + 696
11  AVFoundation                    0x2da500a8 -[AVPlayerLayer layerDidBecomeVisible:] + 200
12  QuartzCore                      0x3106bbf4 CA::Layer::mark_visible(CA::Transaction*, bool) + 80
13  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
14  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
15  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
16  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
17  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
18  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
19  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
20  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
21  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
22  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
23  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
24  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
25  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
26  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
27  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
28  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
29  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
30  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
31  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
32  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
33  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
34  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
35  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
36  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
37  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
38  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
39  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
40  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
41  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
42  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
43  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
44  QuartzCore                      0x3106bc30 CA::Layer::mark_visible(CA::Transaction*, bool) + 140
45  QuartzCore                      0x3106cb82 CA::Layer::set_visible(unsigned int) + 346
46  QuartzCore                      0x3106c9e6 CA::Context::set_layer(void const*) + 134
47  UIKit                           0x313feab2 -[UIWindow _createContext] + 1138
48  UIKit                           0x316572a4 _UIWindowUpdateVisibleContextOrder + 172
49  UIKit                           0x31657158 +[UIWindow _prepareWindowsPassingTestForAppResume:] +         12
50  UIKit                           0x315fc534 -[UIApplication _handleApplicationResumeEvent:] + 72
51  UIKit                           0x313fb60e -[UIApplication handleEvent:withNewEvent:] + 1878
52  UIKit                           0x313fadf4 -[UIApplication sendEvent:] + 68
53  UIKit                           0x3145f400 _UIApplicationHandleEvent + 612
54  GraphicsServices                0x33a68b52 _PurpleEventCallback + 606
55  GraphicsServices                0x33a6873a PurpleEventCallback + 30
56  CoreFoundation                  0x2eb91844     __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 32
57  CoreFoundation                  0x2eb917de __CFRunLoopDoSource1 + 342
58  CoreFoundation                  0x2eb8ffaa __CFRunLoopRun + 1402
59  CoreFoundation                  0x2eafa764 CFRunLoopRunSpecific + 520
60  CoreFoundation                  0x2eafa546 CFRunLoopRunInMode + 102
61  GraphicsServices                0x33a676ce GSEventRunModal + 134
62  UIKit                           0x3145988c UIApplicationMain + 1132
63  myapp                           0x0003ba0e main (main.m:14)
64  myapp                           0x0003b9c4 start + 36

基本上我使用 UIWebView 通过 YouTube HTML 播放器加载 HTML 文件，并使用 [webView stringByEvaluatingJavaScriptFromString: jsString] 来控制它(如 loadVideoById( ), play(), pause() 等)。还有一些机制可以让应用程序在后台播放视频，大多数时候它运行良好，这个崩溃只发生在它在后台播放几个视频，并试图进入前台，但很难重现。

似乎 webthread 正在锁定主线程，所以 iOS 杀死了我的应用程序，我已经研究了这个问题几个星期但没有运气，欢迎任何建议。

Answer 1

经过大量实验，可以通过在应用进入后台时使用 CSS 隐藏 html 播放器 div 标签来避免此问题，然后在 AFTER 收到 appDidBecomeActive 事件后再次显示它。

我认为 YouTube html 播放器正在尝试在应用程序激活时执行一些与 UI 相关的操作，因此它可能会锁定主线程并导致 0x000000008badf00d 崩溃。

希望这个回答可以帮助到一些人。