Question

这是我的代码：

@interface MyObject ()
@property(nonatomic) dispatch_queue_t queue;
@end

@implementation MyObject {
    NSThread *_check;
}

- (id)init {
    self = [super init];
    if (self) {
        _queue = dispatch_queue_create("com.Thread.queue", NULL);
        dispatch_async(_queue, ^{
            _check = [NSThread currentThread]; //for ex. thread number = 3
            //some code here...
        });
    }

    return self;
}

- (void)someMethod:(MyObjClass *)obj {
    dispatch_async(_queue, ^{
        //need th
        if (_check != [NSThread currentThread]) { // it is sometimes number 3, but sometimes it changes
            NSLog(@"Thread changed.");
        }
        [obj doSmth]; //got crash if currentThread != _check         
    });
}

@end

我需要确保所有MyObjClass的方法在同一个线程中执行。但是这个代码通过它自己的意愿来改变线程，但有时它在单线程中工作。我可以用任何方式强制它一直使用相同的线程吗？

Answer 1

总之，没有。除了主队列之外，GCD没有任何线程关联的概念。如果你真的需要线程亲和力，GCD并不是真正的正确工具。如果你喜欢这个成语，并希望根据自己的需要“适应”某些东西，你可以这样做：

@implementation AppDelegate
{
    NSThread* thread;
}

void dispatch_thread_async(NSThread* thread, dispatch_block_t block)
{
    if ([NSThread currentThread] == thread)
    {
        block();
    }
    else
    {
        block = [block copy];
        [(id)block performSelector: @selector(invoke) onThread: thread withObject: nil waitUntilDone: NO];
    }
}

void dispatch_thread_sync(NSThread* thread, dispatch_block_t block)
{
    if ([NSThread currentThread] == thread)
    {
        block();
    }
    else
    {
        [(id)block performSelector: @selector(invoke) onThread: thread withObject: nil waitUntilDone: YES];
    }
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
    thread = [[NSThread alloc] initWithTarget: self selector:@selector(threadMain) object:nil];
    [thread start];

    dispatch_thread_async(thread, ^{
        NSLog(@"Async Thread: %@", [NSThread currentThread]);
    });

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        dispatch_thread_sync(thread, ^{
            NSLog(@"Sync Thread: %@", [NSThread currentThread]);
        });
    });
}

- (void)threadMain
{
    // You need the NSPort here because a runloop with no sources or ports registered with it
    // will simply exit immediately instead of running forever.
    NSPort* keepAlive = [NSPort port];
    NSRunLoop* rl = [NSRunLoop currentRunLoop];
    [keepAlive scheduleInRunLoop: rl forMode: NSRunLoopCommonModes];
    [rl run];
}

@end

Answer 2

如果您有多个类的实例，则会使用每个新的init覆盖您的队列。

可以使用单例或静态来解决问题。

任何使dispatch_queue_t在单线程中工作的方法？

2 个答案: