iOS dispatch队列

• 多线程09CGD队列组

• 一需求说明
• 二通知使用 dispatch_group_notify

• 1 队列组的使用可以分为四个步骤
• 2 示例代码
• 2 结果

• 三通知使用 dispatch_group_wait

• 1 示例代码
• 2 结果

• 三dispatch_group_enter 和 dispatch_group_leave 配套使用

• 1 说明
• 2 示例代码
• 3 结果

多线程09——CGD队列组

一、需求说明

有这么1种需求

首先：分别异步执行2个耗时的操作

其次：等2个异步操作都执行完毕后，再回到主线程执行操作

如何解决？？

当然我们可以使用 异步函数 + 并发队列 + 栅栏函数 来解决这问题。 除此之外，如果想要快速高效地实现上述需求，可以考虑用 队列组

dispatch_group_t group =  dispatch_group_create();
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // 执行1个耗时的异步操作
});

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // 执行1个耗时的异步操作
});

dispatch_group_notify(group, dispatch_get_main_queue(), ^{
    // 等前面的异步操作都执行完毕后，回到主线程...
});

二、通知使用 dispatch_group_notify

2.1 队列组的使用可以分为四个步骤

1.创建队列

2.创建队列组

3.封装任务

4.拦截通知

2.2 示例代码

-(void)group1{
    //1.创建队列
    dispatch_queue_t queue =  dispatch_get_global_queue(0, 0);

    //2.创建队列组
    dispatch_group_t group = dispatch_group_create();

    //3.封装任务
    dispatch_group_async(group, queue, ^{
        NSLog(@"1----------%@",[NSThread currentThread]);
    });

    dispatch_group_async(group, queue, ^{
        NSLog(@"2----------%@",[NSThread currentThread]);
    });

    dispatch_group_async(group, queue, ^{
        NSLog(@"3----------%@",[NSThread currentThread]);
    });

    //4.拦截通知
    dispatch_group_notify(group, queue, ^{
        NSLog(@"---dispatch_group_notify------%@",[NSThread currentThread]);
    });
    //不用等待 队列执行完就会执行这个代码
    NSLog(@"----group1--end----");
}

2.2 结果

2017-09-03 04:09:35.086 03_UIview83多线程GCD[86781:501798] ----group1--end----
2017-09-03 04:09:35.086 03_UIview83多线程GCD[86781:502228] 1----------<NSThread: 0x60000007aa00>{number = 3, name = (null)}
2017-09-03 04:09:35.086 03_UIview83多线程GCD[86781:502234] 2----------<NSThread: 0x600000076fc0>{number = 4, name = (null)}
2017-09-03 04:09:35.086 03_UIview83多线程GCD[86781:502235] 3----------<NSThread: 0x608000262a80>{number = 5, name = (null)}
2017-09-03 04:09:35.086 03_UIview83多线程GCD[86781:502235] ---dispatch_group_notify------<NSThread: 0x608000262a80>{number = 5, name = (null)}

---

三、通知使用 dispatch_group_wait

3.1 示例代码

-(void)group2{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, queue, ^{
        NSLog(@"1----------%@",[NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"2----------%@",[NSThread currentThread]);
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"3----------%@",[NSThread currentThread]);
    });
    //等待，DISPATCH_TIME_FOREVER 知道队列中所有的任务执行完成了才能执行
    dispatch_group_wait(group,DISPATCH_TIME_FOREVER);
    //最后执行
    NSLog(@"----group2--end----");
}

3.2 结果

2017-09-03 04:14:47.246 03_UIview83多线程GCD[87259:508074] 2----------<NSThread: 0x6000000718c0>{number = 4, name = (null)}
2017-09-03 04:14:47.246 03_UIview83多线程GCD[87259:508069] 1----------<NSThread: 0x600000071100>{number = 3, name = (null)}
2017-09-03 04:14:47.246 03_UIview83多线程GCD[87259:508075] 3----------<NSThread: 0x608000074000>{number = 5, name = (null)}
2017-09-03 04:14:47.247 03_UIview83多线程GCD[87259:504674] ----group2--end----

---

三、dispatch_group_enter 和 dispatch_group_leave 配套使用

4.1 说明

dispatch_group_enter 方法后面的异步任务会被纳入到队列组的监听范围,进入群组

dispatch_group_enter | dispatch_group_leave 必须要配对使用

“`
void
dispatch_group_enter(dispatch_group_t group);

void
dispatch_group_leave(dispatch_group_t group);
“`

4.2 示例代码

-(void)group3{
    dispatch_queue_t queque = dispatch_get_global_queue(0, 0);
    dispatch_group_t group = dispatch_group_create();
    //在该方法后面的异步任务会被纳入到队列组的监听范围,进入群组
    //dispatch_group_enter|dispatch_group_leave 必须要配对使用
    dispatch_group_enter(group);
    dispatch_async(queque, ^{
         NSLog(@"1----------%@",[NSThread currentThread]);
        dispatch_group_leave(group);
    });
    dispatch_group_enter(group);
    dispatch_async(queque, ^{
        NSLog(@"2----------%@",[NSThread currentThread]);
        dispatch_group_leave(group);
    });
    //等待，DISPATCH_TIME_FOREVER 知道队列中所有的任务执行完成了才能执行
    dispatch_group_wait(group,DISPATCH_TIME_FOREVER);
    NSLog(@"----group3--end----");
}

4.3 结果

2017-09-03 04:15:42.832 03_UIview83多线程GCD[87781:509477] 1----------<NSThread: 0x600000269f00>{number = 3, name = (null)}
2017-09-03 04:15:42.832 03_UIview83多线程GCD[87781:509482] 2----------<NSThread: 0x600000269f40>{number = 4, name = (null)}
2017-09-03 04:15:42.832 03_UIview83多线程GCD[87781:508866] ----group3--end----