GCD 编程详解

//  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： static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{     // code to be executed once }); // 延迟2秒执行： 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 }); // 自定义dispatch_queue_t dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL); dispatch_async(urls_queue, ^{  　 　// your code  }); dispatch_release(urls_queue); // 合并汇总结果 dispatch_group_t group = dispatch_group_create(); dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{      // 并行执行的线程一 }); dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{      // 并行执行的线程二 }); dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{      // 汇总结果 });