DCG语法

后台执行：dispatch_async(dispatch_get_global_queue(0,0), ^{

something});

主线程执行：dispatch_async(dispatch_get_main_queue(), ^{

something});

一次性执行：staticdispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

code to be executed once});

延迟2秒执行：doubledelayInSeconds =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});

dispatch_queue_t 也可以自己定义，如要要自定义queue，可以用dispatch_queue_create方法，示例如下：

dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);

dispatch_async(urls_queue,^{

your code});

dispatch_release(urls_queue);