NSOperationQueue 随机暂停？

Question

我有一个大量使用 NSOperationQueue 的应用程序。

有时我注意到一些 NSOperationQueues 会“锁定”或随机进入“isSuspished”状态，即使我的代码从未调用 setSuspished: 方法。

这是不可能复制的，而且很难调试，因为每当我将设备连接到 Xcode 进行调试时，应用程序就会重新加载，错误就会消失。

我在所有可能出现问题的点添加了很多 NSLog，并且只需要使用该应用程序几天，直到错误再次出现。

查看设备系统日志，我发现 [myOperationQueue operationCount] 会增加，但队列中的操作不会执行。

我还没有尝试手动设置“setSuspished：NO”，但这真的有必要吗？

可能是什么原因造成的？

这是我的代码的一小部分

调用操作的视图控制器

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        self.operationQueue = [[[NSOperationQueue alloc] init] autorelease];
        [self.operationQueue setMaxConcurrentOperationCount:2];

        self.sendOperationQueue = [[[NSOperationQueue alloc] init] autorelease];
        [self.sendOperationQueue setMaxConcurrentOperationCount:2];

        self.receiveOperationQueue = [[[NSOperationQueue alloc] init] autorelease];
        [self.receiveOperationQueue setMaxConcurrentOperationCount:1];
    }
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];

    [operationQueue cancelAllOperations];
    [sendOperationQueue cancelAllOperations];
    [receiveOperationQueue cancelAllOperations];

    [operationQueue release];
    [sendOperationQueue release];
    [receiveOperationQueue release];
}

- (IBAction)sendMessage
{
    if(![chatInput.text isEqualToString:@""])
    {
        NSString *message = self.chatInput.text;
        SendMessageOperation *sendMessageOperation = [[SendMessageOperation alloc] initWithMatchData:matchData andMessage:message resendWithKey:nil];
        [self.sendOperationQueue addOperation:sendMessageOperation];
        [sendMessageOperation release];
    }
}

NSOperation 子类 SendMessageOperation

- (id)initWithMatchData:(MatchData*)data andMessage:(NSString*)messageString resendWithKey:(NSString*)resendKey
{
self = [super init];

    if(self != nil)
    {
        if(data == nil || messageString == nil)
        {
            [self release];
            return nil;
        }
        appDelegate = (YongoPalAppDelegate *) [[UIApplication sharedApplication] delegate];

        context = [[NSManagedObjectContext alloc] init];
        [context setPersistentStoreCoordinator:[appDelegate persistentStoreCoordinator]];
        [context setMergePolicy:NSMergeByPropertyObjectTrumpMergePolicy];

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeContextChanges:) name:NSManagedObjectContextDidSaveNotification object:context];

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeMainContextChanges:) name:NSManagedObjectContextDidSaveNotification object:appDelegate.managedObjectContext];

        self.matchData = (MatchData*)[context objectWithID:[data objectID]];
        matchNo = [[matchData valueForKey:@"matchNo"] intValue];
        partnerNo = [[matchData valueForKey:@"partnerNo"] intValue];

        self.message = messageString;
        self.key = resendKey;

        apiRequest = [[APIRequest alloc] init];
    }
    return self;
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];

    self.matchData = nil;
    self.message = nil;
    self.key = nil;
    [context release];
    [apiRequest release];
    [super dealloc];
}

- (void)start
{
    if([self isCancelled] == YES)
    {
        [self willChangeValueForKey:@"isFinished"];
        finished = YES;
        [self didChangeValueForKey:@"isFinished"];
        return;
    }
    else
    {
        [self willChangeValueForKey:@"isExecuting"];
        executing = YES;
        [self main];
        [self didChangeValueForKey:@"isExecuting"];
    }
}

- (void)main
{
    @try
    {
        NSAutoreleasePool *pool = [NSAutoreleasePool new];

        bool taskIsFinished = NO;
        while(taskIsFinished == NO && [self isCancelled] == NO)
        {
            NSDictionary *requestData = nil;

            if(key == nil)
            {
                requestData = [self sendMessage];
            }
            else
            {
                requestData = [self resendMessage];
            }

            NSDictionary *apiResult = nil;
            if(requestData != nil)
            {
                apiResult = [self sendMessageToServer:requestData];
            }

            if(apiResult != nil)
            {                
                [[NSNotificationCenter defaultCenter] postNotificationName:@"shouldConfirmSentMessage" object:nil userInfo:apiResult];
            }

            taskIsFinished = YES;
        }

        [self willChangeValueForKey:@"isFinished"];
        [self willChangeValueForKey:@"isExecuting"];
        finished = YES;
        executing = NO;
        [self didChangeValueForKey:@"isFinished"];
        [self didChangeValueForKey:@"isExecuting"];

        [pool drain];
    }
    @catch (NSException *e)
    {
        NSLog(@"Exception %@", e);
    }
}

- (BOOL)isConcurrent
{
    return YES;
}

- (BOOL)isFinished
{
    return finished;
}

- (BOOL)isExecuting
{
    return executing;
}

- (void)mergeContextChanges:(NSNotification *)notification
{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"mergeChatDataChanges" object:nil userInfo:[notification userInfo]];
}

- (void)mergeMainContextChanges:(NSNotification *)notification
{
    NSSet *updated = [[notification userInfo] objectForKey:NSUpdatedObjectsKey];
    for(NSManagedObject *thing in updated)
    {
        [[context objectWithID:[thing objectID]] willAccessValueForKey:nil];
    }

    [context mergeChangesFromContextDidSaveNotification:notification];
}

Answer 1

您正在使用：

setMaxConcurrentOperationCount:X

我的预感是队列中的 X 个操作尚未完成，因此导致添加到队列中的任何后续操作在这种情况之前不会运行。

Answer 2

来自 NSOperationQueue 的 isSuspended 方法文档：

如果想知道队列的挂起状态何时发生变化，可以配置一个KVO观察者来观察操作队列的挂起键路径。

您可以与观察者并行实现的另一个想法是创建一个 NSOperationQueue 的子类来重新定义 setSuspished: 方法。在重新定义的版本中，如果您在调试器上运行，则可以设置断点；如果您在不带调试器的情况下运行，则可以将堆栈跟踪打印到日志中。

希望这有帮助。

Answer 3

看一下 ASIHTTPRequestConfig.h，它有一些标志，您可以打开它们来查看幕后真正发生的情况。