I have a ViewController which fetch data in AddressBook. To be notified when data has been fetched, I post a notification to this ViewController to allow it to update a NSViewTable (in the main queue).This ViewController is presented with a transient NSPopover, when a user ends editing a NSTextField in the ViewController view.
When I enter a first string in this field, the popover is displayed then is closed when the user has finishing interacting with it. If I edit again the Text Field, the Popover do not appear in view, but the fetching process starts. When it ends and the DataUpdated method devoted to the notification post is fired. Then I got a crash on the dispatch_sync(dispatch_get_main_queue(), ^{ line itself (no message in console, even with NSZombie enabled). Here is the code in the popover content ViewController:
- (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:)];
}
Any idea of what's happen? The error message in the source code is Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
The Backtrace is:
#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 ()
Your dataUpdated method uses dispatch_sync to call through to the main thread:
- (void) DataUpdated
{
dispatch_sync(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
});
}
You want to make sure that this notification is sent only on the main thread, which is a good idea. The problem occurs when, as can be clearly seen from the backtrace, this method gets sent from the main thread. It's easy to see why this is a problem; dispatch_sync waits until the block you give it completes, but if you try to run the block on the main queue, and the main thread is blocking waiting for dispatch_sync to complete, the main thread's going to be deadlocked forever, and your app is essentially hung. Now, why it's crashing with EXC_BAD_INSTRUCTION I'm not sure, but it's doing that on my machine too when I try it. I'm pretty sure that it just hung the first time I did this by accident as a wee bab, so who knows. Perhaps they've added some protection at some point to detect this scenario and just crash, so that you can get a nice backtrace to figure out what happened.
In any event, we just need to avoid blocking the main thread while waiting for the main thread. If you dispatch_async instead of dispatch_sync, this'll work great:
- (void) DataUpdated
{
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:@"DataUpdateNotification" object:self];
});
}
dispatch_async doesn't block while waiting for the block to complete, so it won't deadlock. The bad news is that the notification won't be fired immediately; it'll wait until the next spin of the event loop. If that's a problem, just check for the main thread, like this:
- (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);
}
}
This will ensure that the notification is always sent immediately, and the method always waits until it's finished sending. If you do this sort of thing often, you can write the above as a utility function that takes an arbitrary block and runs it synchronously on the main thread.