GCD簡單使用

一.普通使用

1.後臺執行

dispatch_async(dispatch_get_global_queue(0, 0), ^{
     // something
});

2.主執行緒執行

dispatch_async(dispatch_get_main_queue(), ^{
     // something
});

3.一次性執行

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    // code to be executed once
});

4.延遲兩秒執行

double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    // code to be executed on the main queue after delay
});

自定義使用

1.自定義佇列

dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);
dispatch_async(urls_queue, ^{
     // your code
});
dispatch_release(urls_queue);

2.兩個佇列並行執行，執行完之後回撥一個Block

dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
     // 並行執行的執行緒一
});
dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
     // 並行執行的執行緒二
});
dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{
     // 彙總結果
});