ios GCD一些使用方法

 1 - (void)GCDMethed{
 2     // 后台执行
 3     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
 4         
 5         // 后台执行的操作
 6         NSLog(@"后台操作");
 7     });
 8     
 9     // 主线程执行
10     dispatch_async(dispatch_get_main_queue(), ^{
11        
12         // 主线程执行的操作
13         NSLog(@"主线程操作");
14     });
15     
16     
17     // 一次性执行
18     for (int i=0; i<2; i++) {
19         static  dispatch_once_t onceToken;
20         dispatch_once(&onceToken, ^{
21             // 代码执行一次
22             NSLog(@"代码执行一次");
23         });
24     }
25     
26 //    延迟2秒执行
27     double delayInSeconds = 2.0;
28     dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
29     dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
30         NSLog(@"延迟了2秒执行");
31     });
32     
33     // 自定义 dispatch_queue_t
34     dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);
35     dispatch_queue_t urls_queue2 = dispatch_queue_create("TEST",DISPATCH_QUEUE_CONCURRENT); // 并行的队列 DISPATCH_QUEUE_SERIAL 穿行队列
36     dispatch_async(urls_queue, ^{
37         
38     });
39 //    dispatch_release(urls_queue);  ARC 不需要
40     
41     
42     // 合并汇总结果
43     
44     dispatch_group_t group  = dispatch_group_create();
45     dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
46             // 并行执行的线程一
47     });
48     dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
49             // 并行执行的线程二
50     });
51     dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
52             // 汇总结果
53     });
54     
55     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
56        
57         dispatch_async(dispatch_get_main_queue(), ^{
58             
59         });
60     });
61     
62 }