GCD应用及其他方法

1.GCD应用 单例模式
   
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
   
        NSLog(@"执行一次%@",[NSThread currentThread]);
       

});

2.延迟操作
    //1、
    NSLog(@"开始执行");
   
    //    [self performSelector:@selector(handleAction) withObject:nil afterDelay:0];
   
    //2、
   
    //DISPATCH_TIME_NOW 从现在开始
    //delayInSeconds 延迟几秒
   
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC));
   
    //    when dispatch_time_t
   
    dispatch_after(time, dispatch_get_main_queue(), ^{
       
        NSLog(@"%@",[NSThread currentThread]);
       
    });

3.调度组

//创建调度组
    dispatch_group_t group = dispatch_group_create();
    //获取全局队列
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    //调度组的异步请求
    dispatch_group_async(group, queue, ^{
       
        [NSThread sleepForTimeInterval:2];
        NSLog(@"下载第一张图");
    });
    dispatch_group_async(group, queue, ^{
        [NSThread sleepForTimeInterval:3];
       
        NSLog(@"下载第二张图");
    });
    dispatch_group_async(group, queue, ^{
        [NSThread sleepForTimeInterval:1];
       
        NSLog(@"下载第三张图");
    });
    dispatch_group_async(group, queue, ^{
        [NSThread sleepForTimeInterval:5];
       
        NSLog(@"下载第四张图");
    });
    //notify通知，当所有异步请求完成时调用dispatch_group_notify
    dispatch_group_notify(group, queue, ^{
        NSLog(@"更新UI");
    });

4.调度组的第二种方式

//创建调度组
    dispatch_group_t group = dispatch_group_create();
    //获取全局队列
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
   
    //进入队列
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:2];
        NSLog(@"下载第一张图");
       
        //离开队列
        dispatch_group_leave(group);
    });
   
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:1];
        NSLog(@"下载第er张图");
       
        dispatch_group_leave(group);
    });
   
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:3];
        NSLog(@"下载第san张图");
       
        dispatch_group_leave(group);
    });
   
    //等待调度队列wait相当于一个阻塞状态 等最后一个异步进程执行后，更新UI才执行
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
   
    NSLog(@"更新UI");

5.中断操作

//dispatch_barrier_async一定是自定义队列
    //这里指定的并发队列应该是自己通过dispatch_queue_create函数创建的。如果你传的是一个串行队列或者全局并发队列，这个函数等同于dispatch_async函数。
   
    dispatch_queue_t queue = dispatch_queue_create("com.blogcn", DISPATCH_QUEUE_CONCURRENT); //dispatch_get_global_queue(0, 0);
   
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"1");
    });
   
    dispatch_async(queue, ^{
        [NSThread sleepForTimeInterval:3];
       
        NSLog(@"2");
    });
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:2];
       
        NSLog(@"3");
    });
   
    //中断操作dispatch_barrier_async
    dispatch_barrier_async(queue, ^{
        NSLog(@"--------");
        [NSThread sleepForTimeInterval:1];
       
    });
   
    dispatch_async(queue, ^{
       
        [NSThread sleepForTimeInterval:1];
        NSLog(@"4");
    });
    dispatch_async(queue, ^{
        NSLog(@"5");
    });

6.遍历

//遍历操作
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    //iterations 遍历的次数
    dispatch_apply(5, queue, ^(size_t i) {
        NSLog(@"%@",@(i));
    });