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IOS GCD 常用

dispatch queue分成以下三种:

1)运行在主线程的Main queue,通过dispatch_get_main_queue获取。

2)并行队列global dispatch queue,通过dispatch_get_global_queue获取,由系统创建三个不同优先级的dispatch queue。并行队列的执行顺序与其加入队列的顺序相同。

3)串行队列serial queues一般用于按顺序同步访问,可创建任意数量的串行队列,各个串行队列之间是并发的。

//  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
 });




IOS GCD 常用