ios多线程之GCD

浏览数：22 / 时间：2015年06月11日

　　ios中得多线程技术主要使用3种：NSThread、NSOperation和GCD,这里主要讲GCD

　　GCD:（Grand Central Dispatch）是一种多核编码技术，用纯C语言编写。

　　异步：具备开启线程的功能

　　同步：不具备开启线程的功能

　　并行队列：多个任务可以同时执行

　　串行队列：执行完一个任务后再执行下一个任务

　　下面来进行验证：

 1 // 自定义异步方法
 2 - (void)async:(dispatch_queue_t)queue
 3 {
 4     // 异步执行
 5     dispatch_async(queue, ^{
 6         
 7         NSLog(@"im1-%@",[NSThread currentThread]);
 8     });
 9     dispatch_async(queue, ^{
10         
11         NSLog(@"im2-%@",[NSThread currentThread]);
12     });
13     dispatch_async(queue, ^{
14         
15         NSLog(@"im3-%@",[NSThread currentThread]);
16     });
17     dispatch_async(queue, ^{
18         
19         NSLog(@"im4-%@",[NSThread currentThread]);
20     });
21 
22 }

 1 // 自定义同步方法
 2 - (void)sync:(dispatch_queue_t)queue
 3 {
 4     // 同步执行
 5     dispatch_sync(queue, ^{
 6         
 7         NSLog(@"im1-%@",[NSThread currentThread]);
 8     });
 9     dispatch_sync(queue, ^{
10         
11         NSLog(@"im2-%@",[NSThread currentThread]);
12     });
13     dispatch_sync(queue, ^{
14         
15         NSLog(@"im3-%@",[NSThread currentThread]);
16     });
17     dispatch_sync(queue, ^{
18         
19         NSLog(@"im4-%@",[NSThread currentThread]);
20     });
21 
22 }

调用异步执行方法：

1 // 创建一个全局并行队列
2     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
3     
4     // 异步执行
5     [self async:queue];

最终的结果为：开启了四个线程,并且执行顺序是不定

1 2015-04-02 16:29:20.438 GCD[4398:1f07] im3-<NSThread: 0x7177ee0>{name = (null), num = 5}
2 2015-04-02 16:29:20.432 GCD[4398:1303] im1-<NSThread: 0x7177d70>{name = (null), num = 3}
3 2015-04-02 16:29:20.440 GCD[4398:4307] im4-<NSThread: 0x7178490>{name = (null), num = 6}
4 2015-04-02 16:29:20.432 GCD[4398:1a03] im2-<NSThread: 0x75429f0>{name = (null), num = 4}

1 // 创建一个全局串行队列
2     dispatch_queue_t queue = dispatch_queue_create("wys", NULL);
3     
4     // 异步执行
5     [self async:queue];

最终的结果为：开启了一个线程,执行顺序为从上往下依次执行

1 2015-04-02 16:32:19.415 GCD[4442:1303] im1-<NSThread: 0x71631a0>{name = (null), num = 3}
2 2015-04-02 16:32:19.428 GCD[4442:1303] im2-<NSThread: 0x71631a0>{name = (null), num = 3}
3 2015-04-02 16:32:19.437 GCD[4442:1303] im3-<NSThread: 0x71631a0>{name = (null), num = 3}
4 2015-04-02 16:32:19.450 GCD[4442:1303] im4-<NSThread: 0x71631a0>{name = (null), num = 3}

调用主队列执行方法：

1 // 创建主队列
2     dispatch_queue_t queue = dispatch_get_main_queue();
3     
4     // 异步执行
5     [self async:queue];

最红的结果为：顺序执行并且不开启线程，在主线程中执行

1 2015-04-02 16:35:45.320 GCD[4484:c07] im1-<NSThread: 0x71560c0>{name = (null), num = 1}
2 2015-04-02 16:35:45.333 GCD[4484:c07] im2-<NSThread: 0x71560c0>{name = (null), num = 1}
3 2015-04-02 16:35:45.339 GCD[4484:c07] im3-<NSThread: 0x71560c0>{name = (null), num = 1}
4 2015-04-02 16:35:45.347 GCD[4484:c07] im4-<NSThread: 0x71560c0>{name = (null), num = 1}

1 // 创建主队列
2     dispatch_queue_t queue = dispatch_get_main_queue();
3     
4     NSLog(@"start");
5     
6     // 同步执行
7     [self sync:queue];
8     
9     NSLog(@"end");

最终的结果为：执行到start就卡住了，不能往下执行

1 2015-04-02 16:38:12.856 GCD[4514:c07] start

调用同步执行方法：

1 // 创建全局并行队列
2     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
3     
4     // 同步执行
5     [self sync:queue];

最终的结果为：不开启线程，并且顺序执行，直接主线程执行

1 2015-04-02 16:41:27.448 GCD[4555:c07] im1-<NSThread: 0x71133c0>{name = (null), num = 1}
2 2015-04-02 16:41:27.458 GCD[4555:c07] im2-<NSThread: 0x71133c0>{name = (null), num = 1}
3 2015-04-02 16:41:27.468 GCD[4555:c07] im3-<NSThread: 0x71133c0>{name = (null), num = 1}
4 2015-04-02 16:41:27.472 GCD[4555:c07] im4-<NSThread: 0x71133c0>{name = (null), num = 1}

1 // 创建串行队列
2     dispatch_queue_t queue = dispatch_queue_create("wys", NULL);
3     
4     // 同步执行
5     [self sync:queue];

最终的结果为：不开启线程，并且顺序执行，直接主线程执行

1 2015-04-02 16:43:40.609 GCD[4589:c07] im1-<NSThread: 0x713e570>{name = (null), num = 1}
2 2015-04-02 16:43:40.621 GCD[4589:c07] im2-<NSThread: 0x713e570>{name = (null), num = 1}
3 2015-04-02 16:43:40.626 GCD[4589:c07] im3-<NSThread: 0x713e570>{name = (null), num = 1}
4 2015-04-02 16:43:40.634 GCD[4589:c07] im4-<NSThread: 0x713e570>{name = (null), num = 1}