GCD创建、开启、暂停、取消定时器

-(void) startGCDTimer{
    NSTimeInterval period = 1.0; //设置时间间隔
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0), period * NSEC_PER_SEC, 0); //每秒执行
    dispatch_source_set_event_handler(_timer, ^{
        //在这里执行事件
        NSLog(@"每秒执行test");
    });
    
    dispatch_resume(_timer);
}
 
 
-(void) pauseTimer{
    if(_timer){
        dispatch_suspend(_timer);
    }
}
-(void) resumeTimer{
    if(_timer){
        dispatch_resume(_timer);
    }
}
-(void) stopTimer{
    if(_timer){
        dispatch_source_cancel(_timer);
        _timer = nil;
    }
}