ios 多线程定时器

@property (strong ,nonatomic) dispatch_source_t time;
//定时器
-(void)timer{

   __weak typeof(self) WeakSelf = self;
   __block NSInteger timer = 0;

   dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
   //    DISPATCH_SOURCE_TYPE_TIMER:定时器类型
   self.time = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
   dispatch_source_set_timer(self.time, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
   dispatch_source_set_event_handler(self.time, ^{

       timer += 1;

       dispatch_async(dispatch_get_main_queue(), ^{
           NSInteger minute = timer/60;
           NSInteger seconds = timer - minute * 60;
           if (minute >= 10) {
               if (seconds >= 10) {

                   WeakSelf.timeLabel.text = [NSString stringWithFormat:@"%ld:%ld",minute,seconds];

               }else{

                   WeakSelf.timeLabel.text = [NSString stringWithFormat:@"%ld:0%ld",minute,seconds];

               }
           }else{

               if (seconds >= 10) {

                   WeakSelf.timeLabel.text = [NSString stringWithFormat:@"0%ld:%ld",minute,seconds];

               }else{

                   WeakSelf.timeLabel.text = [NSString stringWithFormat:@"0%ld:0%ld",minute,seconds];

               }

           }
       });
   });
   dispatch_resume(self.time);
}
//在退出程序时：dispatch_source_cancel(self.time);