几种常见的gcd用法

/**< 自定义queue，默认串行： NULL == DISPATCH_QUEUE_SERIAL*/

    /**< label:标签，用于标注queue*/

//    dispatch_queue_t queue = dispatch_queue_create("label", NULL);

//    

//    dispatch_async(queue, ^{

//        NSLog(@"test");

//    });

 

    /**< 自定义queue，并行或串行： DISPATCH_QUEUE_CONCURRENT或DISPATCH_QUEUE_SERIAL*/

//    dispatch_queue_t serial_queue = dispatch_queue_create("标签", DISPATCH_QUEUE_CONCURRENT);

//    dispatch_async(serial_queue, ^(){

//        sleep(5);

//        NSLog(@"block_1"); // 尽管为异步调用且延迟3秒，但如果在serial队列中，block_1仍然先于block_2被打印出来

//    });

//    dispatch_async(serial_queue, ^(){

//        NSLog(@"block_2");

//    });

     

     /**< 延迟执行*/

    /**< (int64_t)(delayInSeconds * NSEC_PER_SEC)：转换成毫秒*/

//    double delayInSeconds = 5.0;

//    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));

//    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

//        NSLog(@"5s delay");

//    });

     

    /**< 常用的异步并发执行*/

//    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT , 0), ^{

//        sleep(5);

//        NSLog(@"block_1");

//    });

//    

//    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT , 0), ^{

//        NSLog(@"block_2");

//    });

   

    /**< 异步并回调主线程，常用ui更新*/

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        dispatch_async(dispatch_get_main_queue(), ^{

           NSLog(@"to do with ui");  

             

        });

    });