dispatch_get_main_queue 在第二次调用的方法中崩溃

Question

我有一个 ViewController，它在 AddressBook 中获取数据。为了在获取数据时收到通知，我向此 ViewController 发布通知以允许它更新 NSViewTable（在主队列中）。当用户结束在 ViewController 视图中编辑 NSTextField 时，此 ViewController 会显示一个瞬态 NSPopover .

当我在此字段中输入第一个字符串时，弹出窗口将显示，然后在用户完成与其交互时关闭。如果我再次编辑文本字段，Popover 不会出现在视图中，但提取过程开始。当它结束并且DataUpdated专门用于通知帖子的方法被触发时。然后我dispatch_sync(dispatch_get_main_queue(), ^{在线路上崩溃了（控制台中没有消息，即使启用了 NSZombie）。这是弹出内容 ViewController 中的代码：

- (void) getContactForName: (NSString *) name
{

    CNEntityType entityType = CNEntityTypeContacts;
    if ([CNContactStore authorizationStatusForEntityType:entityType]){
        CNContactStore *store = [[CNContactStore alloc] init];
        [store requestAccessForEntityType:entityType completionHandler:^(BOOL granted, NSError * _nullableError){
            if (granted) {
                if ([CNContactStore class]){
                    NSError *contactError;
                    CNContactStore *addressBook = [[CNContactStore alloc] init];
                    [addressBook containersMatchingPredicate:[CNContainer predicateForContainersWithIdentifiers:@[addressBook.defaultContainerIdentifier]] error:&contactError];
                    NSArray * keysToFetch =@[CNContactEmailAddressesKey, CNContactPhoneNumbersKey, CNContactFamilyNameKey, CNContactGivenNameKey, CNContactIdentifierKey];
                    NSError *error;

                    contactList = [addressBook unifiedContactsMatchingPredicate:[CNContact predicateForContactsMatchingName:name] keysToFetch:keysToFetch error:&error];
                    [self DataUpdated];
                }
            }
        }];

    }

}
-(void) receiveDataNotification: (NSNotification *) notification
{
    [table reloadData];
}
- (void) DataUpdated
{
    dispatch_sync(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
    });
}
- (void) viewWillAppear
{
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(receiveDataNotification:)
                                                 name:@"DataUpdateNotification"
                                               object:nil];
    [table  setDoubleAction:@selector(doubleClick:)];
}

知道发生了什么吗？源代码中的错误信息是Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

回溯是：

#0  0x000000010034c266 in _dispatch_barrier_sync_f_slow ()
#1  0x00000001000095e6 in -[ContactViewController DataUpdated] at /myDirectoryPath/ContactViewController.m:46
#2  0x0000000100009ea4 in __43-[ContactViewController getContactForName:]_block_invoke at /myDirectoryPath/ContactViewController.m:88
#3  0x00007fffae259a29 in -[CNFutureCompletionBlocks addSuccessBlock:orCallWithFutureResult:] ()
#4  0x00007fffa28eeb4a in -[CNContactStore requestAccessForEntityType:completionHandler:] ()
#5  0x0000000100009b30 in -[ContactViewController getContactForName:] at /myDirectoryPath/ContactViewController.m:78
#6  0x00000001000132dc in -[MainViewController getContactsForName:] at /myDirectoryPath/MainViewController.m:437
#7  0x0000000100013391 in -[MainViewController controlTextDidEndEditing:] at /myDirectoryPath/MainViewController.m:444
#8  0x00007fffa2ee854c in __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ ()
#9  0x00007fffa2ee844b in _CFXRegistrationPost ()
#10 0x00007fffa2ee81b2 in ___CFXNotificationPost_block_invoke ()
#11 0x00007fffa2ea6782 in -[_CFXNotificationRegistrar find:object:observer:enumerator:] ()
#12 0x00007fffa2ea576b in _CFXNotificationPost ()
#13 0x00007fffa48e7677 in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#14 0x00007fffa0b96081 in -[NSTextField textDidEndEditing:] ()
#15 0x00007fffa2ee854c in __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ ()
#16 0x00007fffa2ee844b in _CFXRegistrationPost ()
#17 0x00007fffa2ee81b2 in ___CFXNotificationPost_block_invoke ()
#18 0x00007fffa2ea6782 in -[_CFXNotificationRegistrar find:object:observer:enumerator:] ()
#19 0x00007fffa2ea576b in _CFXNotificationPost ()
#20 0x00007fffa48e7677 in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#21 0x00007fffa0d22099 in -[NSTextView(NSPrivate) _giveUpFirstResponder:] ()
#22 0x00007fffa0b822b7 in -[NSTextView doCommandBySelector:] ()
#23 0x00007fffa0b821d1 in -[NSTextInputContext(NSInputContext_WithCompletion) doCommandBySelector:completionHandler:] ()
#24 0x00007fffa0b5fe00 in -[NSKeyBindingManager(NSKeyBindingManager_MultiClients) interpretEventAsCommand:forClient:] ()
#25 0x00007fffa13a17b1 in __84-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:]_block_invoke.1096 ()
#26 0x00007fffa13a15e5 in __84-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:]_block_invoke_3 ()
#27 0x00007fffa0b67f59 in -[NSTextInputContext tryHandleEvent_HasMarkedText_withDispatchCondition:dispatchWork:continuation:] ()
#28 0x00007fffa13a1560 in __84-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:]_block_invoke.1086 ()
#29 0x00007fffa246489f in __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_5 ()
#30 0x00007fffa24636e2 in ___ZL23DispatchEventToHandlersP14EventTargetRecP14OpaqueEventRefP14HandlerCallRec_block_invoke ()
#31 0x00007fffa139a4f8 in __55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke.314 ()
#32 0x00007fffa0b61835 in __55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke_2 ()
#33 0x00007fffa0b617b4 in -[NSTextInputContext tryHandleTSMEvent_HasMarkedText_withDispatchCondition:dispatchWork:continuation:] ()
#34 0x00007fffa0b6119f in -[NSTextInputContext handleTSMEvent:completionHandler:] ()
#35 0x00007fffa0b60883 in _NSTSMEventHandler ()
#36 0x00007fffa2409d85 in DispatchEventToHandlers(EventTargetRec*, OpaqueEventRef*, HandlerCallRec*) ()
#37 0x00007fffa2408ff6 in SendEventToEventTargetInternal(OpaqueEventRef*, OpaqueEventTargetRef*, HandlerCallRec*) ()
#38 0x00007fffa2408e3f in SendEventToEventTargetWithOptions ()
#39 0x00007fffa24606d6 in SendTSMEvent_WithCompletionHandler ()
#40 0x00007fffa2460bb1 in __SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler_block_invoke ()
#41 0x00007fffa2460a12 in __SendFilterTextEvent_WithCompletionHandler_block_invoke ()
#42 0x00007fffa2460727 in SendTSMEvent_WithCompletionHandler ()
#43 0x00007fffa2460511 in SendFilterTextEvent_WithCompletionHandler ()
#44 0x00007fffa24601d6 in SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler ()
#45 0x00007fffa245ff8c in __utDeliverTSMEvent_WithCompletionHandler_block_invoke_2 ()
#46 0x00007fffa245fe32 in __utDeliverTSMEvent_WithCompletionHandler_block_invoke ()
#47 0x00007fffa245fbf9 in TSMKeyEvent_WithCompletionHandler ()
#48 0x00007fffa245f948 in __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_4 ()
#49 0x00007fffa245f775 in __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_3 ()
#50 0x00007fffa245f48b in __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_2 ()
#51 0x00007fffa245f1c2 in __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke ()
#52 0x00007fffa245e73a in TSMProcessRawKeyEventWithOptionsAndCompletionHandler ()
#53 0x00007fffa13a13d1 in __84-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:]_block_invoke.1077 ()
#54 0x00007fffa13a0689 in __204-[NSTextInputContext tryTSMProcessRawKeyEvent_orSubstitution:dispatchCondition:setupForDispatch:furtherCondition:doubleSpaceSubstitutionCondition:doubleSpaceSubstitutionWork:dispatchTSMWork:continuation:]_block_invoke.1003 ()
#55 0x00007fffa13a04f3 in -[NSTextInputContext tryTSMProcessRawKeyEvent_orSubstitution:dispatchCondition:setupForDispatch:furtherCondition:doubleSpaceSubstitutionCondition:doubleSpaceSubstitutionWork:dispatchTSMWork:continuation:] ()
#56 0x00007fffa13a0e1b in -[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:] ()
#57 0x00007fffa13a0362 in -[NSTextInputContext _handleEvent:allowingSyntheticEvent:] ()
#58 0x00007fffa0b5f28b in -[NSView interpretKeyEvents:] ()
#59 0x00007fffa0b5f0a1 in -[NSTextView keyDown:] ()
#60 0x00007fffa12c12cc in -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] ()
#61 0x00007fffa12bff0a in -[NSWindow(NSEventRouting) sendEvent:] ()
#62 0x00007fffa11454a8 in -[NSApplication(NSEvent) sendEvent:] ()
#63 0x00007fffa0c210f8 in -[NSApplication _doModalLoop:peek:] ()
#64 0x00007fffa0e01374 in __35-[NSApplication runModalForWindow:]_block_invoke ()
#65 0x00007fffa0c1eb98 in -[NSApplication runModalForWindow:] ()
#66 0x00007fffa2ef222c in __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ ()
#67 0x00007fffa2ed33c4 in __CFRunLoopDoBlocks ()
#68 0x00007fffa2ed2b35 in __CFRunLoopRun ()
#69 0x00007fffa2ed2544 in CFRunLoopRunSpecific ()
#70 0x00007fffa2431ebc in RunCurrentEventLoopInMode ()
#71 0x00007fffa2431bf9 in ReceiveNextEventCommon ()
#72 0x00007fffa2431b26 in _BlockUntilNextEventMatchingListInModeWithFilter ()
#73 0x00007fffa09caa54 in _DPSNextEvent ()
#74 0x00007fffa11467ee in -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] ()
#75 0x00007fffa0c210b6 in -[NSApplication _doModalLoop:peek:] ()
#76 0x00007fffa0e01374 in __35-[NSApplication runModalForWindow:]_block_invoke ()
#77 0x00007fffa0c1eb98 in -[NSApplication runModalForWindow:] ()
#78 0x00007fffa2ef222c in __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ ()
#79 0x00007fffa2ed33c4 in __CFRunLoopDoBlocks ()
#80 0x00007fffa2ed2b35 in __CFRunLoopRun ()
#81 0x00007fffa2ed2544 in CFRunLoopRunSpecific ()
#82 0x00007fffa2431ebc in RunCurrentEventLoopInMode ()
#83 0x00007fffa2431bf9 in ReceiveNextEventCommon ()
#84 0x00007fffa2431b26 in _BlockUntilNextEventMatchingListInModeWithFilter ()
#85 0x00007fffa09caa54 in _DPSNextEvent ()
#86 0x00007fffa11467ee in -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] ()
#87 0x00007fffa09bf3db in -[NSApplication run] ()
#88 0x00007fffa0989e0e in NSApplicationMain ()
#89 0x000000010001eb42 in main at /myDirectoryPath/main.m:12
#90 0x00007fffb8a9e235 in start ()
#91 0x00007fffb8a9e235 in start ()

Answer 1

您的dataUpdated方法用于dispatch_sync调用主线程：

- (void) DataUpdated
{
    dispatch_sync(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
    });
}

您想确保此通知仅在主线程上发送，这是一个好主意。从回溯可以清楚地看出，当这个方法从主线程发送时，就会出现问题。很容易看出为什么这是一个问题；dispatch_sync等待直到您给它的块完成，但是如果您尝试在主队列上运行该块，并且主线程正在阻塞等待dispatch_sync完成，则主线程将永远陷入死锁，您的应用程序实际上已挂起。现在，为什么它会崩溃EXC_BAD_INSTRUCTION我不确定，但是当我尝试它时它也在我的机器上这样做。我很确定它只是在我第一次做这件事时不小心挂了，所以谁知道呢。也许他们在某个时候添加了一些保护来检测这种情况并且只是崩溃，这样你就可以得到一个很好的回溯来弄清楚发生了什么。

无论如何，我们只需要在等待主线程时避免阻塞主线程即可。如果你dispatch_async代替dispatch_sync，这会很好用：

- (void) DataUpdated
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
    });
}

dispatch_async在等待块完成时不会阻塞，所以它不会死锁。坏消息是通知不会立即被触发；它将等到事件循环的下一次旋转。如果这是一个问题，只需检查主线程，如下所示：

- (void) DataUpdated
{
    // hopefully my skills at remembering the $@#%ing block syntax haven't 
    // atrophied due to primarily writing Swift lately
    void (^sendIt)(void) = ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
    };   

    if ([NSThread isMainThread]) {
        sendIt();
    } else {
        dispatch_sync(dispatch_get_main_queue(), sendIt);
    }
}

这将确保通知总是立即发送，并且该方法总是等待直到它完成发送。如果你经常做这种事情，你可以把上面写成一个实用函数，它接受一个任意块并在主线程上同步运行它。