ios - 单独线程中的快速计时器

Question

我有下一个代码:

         private var timer: dispatch_source_t?
         private let queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL)

         private func startTimer() {
                timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue)
                dispatch_source_set_timer(timer!, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 1 * NSEC_PER_SEC)
                dispatch_source_set_event_handler(timer!) {
                    self.process()
                }
                dispatch_resume(timer!)
            }

        private func stopTimer() {
                if timer != nil {
                    dispatch_source_cancel(timer!)
                    timer = nil
                }
            }

        public func callNow() {
            dispatch_async(queue, {self.process()})
        }

           private func process() {
                Log.d(tag, message: "process currentThread=\(NSThread.currentThread())")
            }

为什么我在两个不同的线程中调用了 process 方法？

process currentThread=<NSThread: 0x7f8080e01880>{number = 2, name = (null)} 
  process currentThread=<NSThread: 0x7f8080e03d40>{number = 3, name = (null)} 
  process currentThread=<NSThread: 0x7f8080e03d40>{number = 3, name = (null)} 
  process currentThread=<NSThread: 0x7f8080e03d40>{number = 3, name = (null)}

Answer 1

不要混淆线程和操作队列。一个操作队列中的任务在不同的线程上执行是完全正常的。来自 Apple's documentation :

Serial queues (also known as private dispatch queues) execute one task at a time in the order in which they are added to the queue. The currently executing task runs on a distinct thread (which can vary from task to task) that is managed by the dispatch queue. Serial queues are often used to synchronize access to a specific resource.