遇到问题
Fabric是检测崩溃的工具，适合放置所有执行代码之前，检测后面的崩溃并上传。
于是我想，既然要放置最前，就越前越好吧，于是就把[Fabric with:]加在了Appdelegate的load方法里，这下不会有搜集不到的崩溃了吧，哈哈（真是天真了）。悲剧来了当我们的app启动的时候，发现进入不了主界面，囧。
调用堆栈如下
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0:
0 libsystem_kernel.dylib 0x0000000197e57570 __semwait_signal + 8
1 libsystem_pthread.dylib 0x0000000197ef76d0 pthread_join + 472
2 vImage 0x00000001849dd678 InitCGInterfacesOnAnotherThread + 240
3 libdispatch.dylib 0x0000000197d11950 _dispatch_client_callout + 12
4 libdispatch.dylib 0x0000000197d12828 dispatch_once_f + 92
5 vImage 0x00000001849dd580 LoadCGInterfaces + 64
6 vImage 0x00000001849d0da4 vImageConverter_CreateCGPassList + 136
7 vImage 0x00000001849cf110 vImageConverter_CreateWithCGImageFormat + 116
8 ImageIO 0x00000001870ee888 CGImagePixelDataProviderCreate + 372
9 ImageIO 0x0000000187118a70 CGImagePixelDataProviderCreateConforming + 1772
10 ImageIO 0x00000001870ed288 CGImageDestinationAddImage + 4104
11 UIKit 0x000000018aae7e38 UIImagePNGRepresentation + 576
12 mail 0x0000000100d72dc8 -[FABIcon initWithPNGImageAtPath:size:prerendered:] + 220
13 mail 0x0000000100d76034 -[FABAppIconUtility largestIconInIconNames:prerendered:] + 908
14 mail 0x0000000100d76308 -[FABAppIconUtility iconFromIOS7StyleCFBundleIconsInFieldWithKey:] + 588
15 mail 0x0000000100d766c0 -[FABAppIconUtility fetchApplicationIcon] + 80
16 mail 0x0000000100d75868 -[FABAppIconUtility applicationIcon] + 44
17 mail 0x0000000100d780b4 -[FABApplicationIdentiferModel initWithInstallID:] + 160
18 mail 0x0000000100d731e0 -[Fabric init] + 320
19 mail 0x0000000100d73324 __19+[Fabric sharedSDK]_block_invoke + 32
20 libdispatch.dylib 0x0000000197d11950 _dispatch_client_callout + 12
21 libdispatch.dylib 0x0000000197d12828 dispatch_once_f + 92
22 mail 0x0000000100d732fc +[Fabric sharedSDK] + 104
23 mail 0x0000000100d73478 __15+[Fabric with:]_block_invoke + 72
24 libdispatch.dylib 0x0000000197d11950 _dispatch_client_callout + 12
25 libdispatch.dylib 0x0000000197d12828 dispatch_once_f + 92
26 mail 0x0000000100d73428 +[Fabric with:] + 224
27 mail 0x0000000100739cc4 -[CrashFree prepareInternal] (CrashFree.m:192)
28 mail 0x00000001007391c0 -[CrashFree prepare] (CrashFree.m:61)
29 mail 0x00000001009ba9d0 +[NEMKernelComponentInit nemInit] (NEMKernelComponentInit.m:28)
30 mail 0x0000000100520c18 +[AppDelegate load] (AppDelegate.m:44)
31 libobjc.A.dylib 0x00000001976c1db4 call_load_methods + 612
32 libobjc.A.dylib 0x00000001976c2d18 load_images + 252
33 dyld 0x000000012006de40 dyld::notifySingle(dyld_image_states, ImageLoader const*) + 276
34 dyld 0x0000000120079670 ImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 304
35 dyld 0x00000001200794d8 ImageLoader::processInitializers(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 136
36 dyld 0x00000001200797a0 ImageLoader::runInitializers(ImageLoader::LinkContext const&, ImageLoader::InitializerTimingList&) + 80
37 dyld 0x000000012006e150 dyld::initializeMainExecutable() + 196
38 dyld 0x00000001200718bc dyld::_main(macho_header const*, unsigned long, int, char const**, char const**, char const**, unsigned long*) + 2664
39 dyld 0x000000012006d040 _dyld_start + 64
Thread 1 name: Dispatch queue: com.apple.libdispatch-manager
Thread 1:
0 libsystem_kernel.dylib 0x0000000197e3cc24 kevent64 + 8
1 libdispatch.dylib 0x0000000197d21e6c _dispatch_mgr_invoke + 272
2 libdispatch.dylib 0x0000000197d13998 _dispatch_mgr_thread + 48
Thread 2 name: WebThread
Thread 2:
0 libsystem_kernel.dylib 0x0000000197e570c0 __psynch_mutexwait + 8
1 libsystem_pthread.dylib 0x0000000197ef1490 _pthread_mutex_lock + 416
2 WebCore 0x0000000194772670 _WebTryThreadLock(bool) + 120
3 WebCore 0x00000001947725d4 WebRunLoopLock(__CFRunLoopObserver*, unsigned long, void*) + 40
4 CoreFoundation 0x0000000185e4c2a0 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 28
5 CoreFoundation 0x0000000185e4922c __CFRunLoopDoObservers + 356
6 CoreFoundation 0x0000000185e49700 __CFRunLoopRun + 1076
7 CoreFoundation 0x0000000185d752d0 CFRunLoopRunSpecific + 392
8 WebCore 0x0000000194770890 RunWebThread(void*) + 464
9 libsystem_pthread.dylib 0x0000000197ef3dc4 _pthread_body + 160
10 libsystem_pthread.dylib 0x0000000197ef3d20 _pthread_start + 156
11 libsystem_pthread.dylib 0x0000000197ef0ef4 thread_start + 0
Thread 3 name: JavaScriptCore::BlockFree
Thread 3:
0 libsystem_kernel.dylib 0x0000000197e57078 __psynch_cvwait + 8
1 libsystem_pthread.dylib 0x0000000197ef2f28 _pthread_cond_wait + 620
2 libc++.1.dylib 0x0000000196e3ccac std::__1::condition_variable::wait(std::__1::unique_lock&) + 52
3 JavaScriptCore 0x0000000187369620 JSC::BlockAllocator::blockFreeingThreadMain() + 228
4 JavaScriptCore 0x0000000187364b9c WTF::wtfThreadEntryPoint(void*) + 20
5 libsystem_pthread.dylib 0x0000000197ef3dc4 _pthread_body + 160
6 libsystem_pthread.dylib 0x0000000197ef3d20 _pthread_start + 156
7 libsystem_pthread.dylib 0x0000000197ef0ef4 thread_start + 0
Thread 4 name: JavaScriptCore::Marking
Thread 4:
0 libsystem_kernel.dylib 0x0000000197e57078 __psynch_cvwait + 8
1 libsystem_pthread.dylib 0x0000000197ef2f28 _pthread_cond_wait + 620
2 libc++.1.dylib 0x0000000196e3ccac std::__1::condition_variable::wait(std::__1::unique_lock&) + 52
3 JavaScriptCore 0x0000000187612edc JSC::GCThread::waitForNextPhase() + 152
4 JavaScriptCore 0x0000000187612f80 JSC::GCThread::gcThreadMain() + 88
5 JavaScriptCore 0x0000000187364b9c WTF::wtfThreadEntryPoint(void*) + 20
6 libsystem_pthread.dylib 0x0000000197ef3dc4 _pthread_body + 160
7 libsystem_pthread.dylib 0x0000000197ef3d20 _pthread_start + 156
8 libsystem_pthread.dylib 0x0000000197ef0ef4 thread_start + 0
Thread 5:
0 libsystem_kernel.dylib 0x0000000197e570c0 __psynch_mutexwait + 8
1 libsystem_pthread.dylib 0x0000000197ef1490 _pthread_mutex_lock + 416
2 libobjc.A.dylib 0x00000001976c2c44 load_images + 40
3 dyld 0x000000012006de40 dyld::notifySingle(dyld_image_states, ImageLoader const*) + 276
4 dyld 0x0000000120079670 ImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 304
5 dyld 0x00000001200794d8 ImageLoader::processInitializers(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 136
6 dyld 0x00000001200797a0 ImageLoader::runInitializers(ImageLoader::LinkContext const&, ImageLoader::InitializerTimingList&) + 80
7 dyld 0x0000000120070d34 dyld::runInitializers(ImageLoader*) + 92
8 dyld 0x0000000120076048 dlopen + 784
9 libdyld.dylib 0x0000000197d3db94 dlopen + 68
10 vImage 0x00000001849dcf1c InitCGInterfaces + 44
11 vImage 0x00000001849dd810 InitPthreadWrapper + 8
12 libsystem_pthread.dylib 0x0000000197ef3dc4 _pthread_body + 160
13 libsystem_pthread.dylib 0x0000000197ef3d20 _pthread_start + 156
14 libsystem_pthread.dylib 0x0000000197ef0ef4 thread_start + 0
看上去是死锁了，我去，怎么死锁的呢。仔细观察，我发现Thread 5有调用方法和主线程调用的方法在名字上有相似的地方，InitCGInterfaces这个在主线程和Thread 5都有涉及。于是我有预感，是主线程和Thread 5在争夺资源。继续调查，InitCGInterfacesOnAnotherThread从名字上看是在其他线程执行个什么东东，嗯，应该就是去Thread 5了，再一次坚定了我的猜测。InitCGInterfacesOnAnotherThread上面pthread_join, 貌似在等待Thread 5执行完毕。
接下来看看Thread 5在做什么，libdyld.dylib 0x0000000197d3db94 dlopen + 68,它去加载了一个动态库，这样一来，又重新跑了遍load_images
load_images就是去调用所有类的load方法的入口
load_images的堆栈上方，是加锁的，并处理wait状态
0 libsystem_kernel.dylib 0x0000000197e570c0 __psynch_mutexwait + 8
1 libsystem_pthread.dylib 0x0000000197ef1490 _pthread_mutex_lock + 416
目前为止情况明朗了。
主线程在load_images中发起Thread 5，并在等待Thread 5结束，但Thread 5执行load_images，需要获取load_images的锁，但是这个锁被主线程占用，Thread 5结束不了，就没法释放，导致了死锁
总结
尽量不要在load中做过多复杂是事务，尤其是涉及到锁，多线程方法的代码，容易造成死锁