最近在iOS4.3.3的机器上发现用asi的block会有很大概率产生crash.
用了ARC
crash表现情况为:bool _WebTryThreadLock(bool), 0x20a0fb20: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now...
2 libsystem_c.dylib 0x3388b727 _sigtramp + 34;
3 WebCore 0x31d363bf _ZL17_WebTryThreadLockb + 102;
4 WebCore 0x31d381b1 WebThreadLock + 52;
5 UIKit 0x3317265f -[UITextView dealloc] + 30;
6 CoreFoundation 0x334afc43 -[NSObject(NSObject) release] + 30;
7 snstaoban 0x00190ffb __arclite_objc_storeStrong + 54;
8 snstaoban 0x0001e5ab -[ShareInputView .cxx_destruct] + 106;
9 libobjc.A.dylib 0x3398d961 object_cxxDestructFromClass + 52;
10 libobjc.A.dylib 0x3398fb15 object_cxxDestruct + 12;
11 libobjc.A.dylib 0x3398fb25 objc_destructInstance + 12;
12 libobjc.A.dylib 0x3398d917 object_dispose + 26;
13 CoreFoundation 0x334afee5 -[NSObject(NSObject) dealloc] + 24;
14 UIKit 0x32ffbec7 -[UIView dealloc] + 382;
15 UIKit 0x33058739 -[UIImageView dealloc] + 64;
16 snstaoban 0x0001d485 -[ShareInputView dealloc] + 120;
17 CoreFoundation 0x334afc43 -[NSObject(NSObject) release] + 30;
18 UIKit 0x32fe85f5 -[UIView(Hierarchy) removeFromSuperview] + 364;
19 UIKit 0x32ffbde3 -[UIView dealloc] + 154;
20 CoreFoundation 0x334afc43 -[NSObject(NSObject) release] + 30;
21 UIKit 0x3305400f -[UIViewController dealloc] + 174;
22 snstaoban 0x00070467 -[RootViewController dealloc] + 238;
23 snstaoban 0x00015f21 -[ShareSetViewController dealloc] + 120;
24 CoreFoundation 0x334afc43 -[NSObject(NSObject) release] + 30;
25 snstaoban 0x00190f29 __arclite_objc_release + 20;
26 snstaoban 0x00178723 __destroy_helper_block_160 + 10;
27 libsystem_blocks.dylib 0x365a688f _Block_release + 58;
28 CoreFoundation 0x334e4285 -[__NSMallocBlock release] + 8;
29 snstaoban 0x00190f29 __arclite_objc_release + 20;
30 snstaoban 0x000733a9 __destroy_helper_block_64 + 12;
31 libsystem_blocks.dylib 0x365a688f _Block_release + 58;
32 CoreFoundation 0x334e4285 -[__NSMallocBlock release] + 8;
33 CoreFoundation 0x334b01a1 CFRelease + 68;
34 CoreFoundation 0x334b5ba9 -[__NSArrayM dealloc] + 92;
35 CoreFoundation 0x334afc43 -[NSObject(NSObject) release] + 30;
36 CoreFoundation 0x334b01a1 CFRelease + 68;
37 CoreFoundation 0x334b2ebb _CFAutoreleasePoolPop + 146;
38 libdispatch.dylib 0x30df06a5 _dispatch_worker_thread2 + 372;
39 libsystem_c.dylib 0x33881591 _pthread_wqthread + 264;
40 libsystem_c.dylib 0x33881bc4 _init_cpu_capabilities + 4294967295||dep=58,idx=57
原因是asi的completionBlock和failureBlock在非主线程(Thread 1 name: Dispatch queue: com.apple.root.low-priority)被释放,然后controller, view接着在这个线程被释放导致crash.
测试了5.0一上也是在非主线程被释放, 但是不会导致crash.
但是4.3.3的模拟器block是在主线程被释放.
于是查看asi的代码发现一个trick.
在dealloc里有

#if NS_BLOCKS_AVAILABLE
[self releaseBlocksOnMainThread];
#endif

if NS_BLOCKS_AVAILABLE

• (void)releaseBlocksOnMainThread
  {
  NSMutableArray *blocks = [NSMutableArray array];
  if (completionBlock) {

  [blocks addObject:completionBlock];
  [completionBlock release];
  completionBlock = nil;

  }
  if (failureBlock) {

  [blocks addObject:failureBlock];
  [failureBlock release];
  failureBlock = nil;

  }
  ....
  [[self class] performSelectorOnMainThread:@selector(releaseBlocks:) withObject:blocks waitUntilDone:[NSThread isMainThread]];
  }

// Always called on main thread

• (void)releaseBlocks:(NSArray *)blocks
  {

  // Blocks will be released when this method exits

  }

endif

疑问:
1.blocks变量应该在主线程被释放还是releaseBlocksOnMainThread所在线程?有文档能证明么?
2.releaseBlocks为什么里面什么都不干呢?

另外:我测试解决4.3.3的blockcrash问题就是改掉

• (void)releaseBlocks:(NSMutableArray *)blocks
  {

  // Blocks will be released when this method exits
  [blocks removeAllObjects];//解决4.3.3子线程释放block的bug

  }

不知道这样做是否合理, 如果是合理的为什么作者不这样做呢?