GCD timer

First of all, it should be noted that GCD's timer is different from NSTimer. NSTimer is affected by RunLoop, but GCD's timer is not affected, because RunLoop is also based on GCD (source code is available).

Next, let's look at the specific implementation of the CGD timer (divided into the following steps):

• Create timer

// get queuedispatch_queue_t queue = dispatch_get_global_queue(0, 0);// create timerself.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER,0, 0, queue);

Note: The timer (dispatch_source_t type) here is actually an OC object, so it must be strongly referenced.

• Set the start time and interval time of the timer

// Set various attributes of the timer (when to start the task, how long to execute the task)// The time parameter of GCD is nanoseconds (1 second == 10 9 nanoseconds), NSEC_PER_SEC represents 10 9 nanosecondsdispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0 * NSEC_PER_SEC)); // 3 seconds later than the current timeuint64_t interval = 1.0 * NSEC_PER_SEC; //interval timedispatch_source_set_timer(self.timer, start, interval, 0);

• Set callback

// set callbackdispatch_source_set_event_handler(self.timer, ^{NSLog(@"-----TorSinLee-----");});

• Start timer

// start timerdispatch_resume(self.timer);

• Turn off the timer

//Cancel timerdispatch_cancel(self.timer);

It can be seen that GCD's timer implementation is much more complicated than NSTimer, but the time accuracy of GCD's timer is better than NSTimer.