GCD 串行队列,并发队列和主队列的整理

1.串行队列：Dispatch Queues或者 Serial Queues

同步

 

dispatch_queue_t queue = dispatch_queue_create("zenny_chen_firstQueue", nil);

    dispatch_sync(queue, ^(void) {


        sleep(2-i/50);
        NSLog(@"The sum is: %d", i);

        //flag = YES;
    });
dispatch_release(queue);

 

 

异步

 

dispatch_queue_t queue = dispatch_queue_create("zenny_chen_firstQueue", nil);
    dispatch_async(queue, ^(void) {
        sleep(2-i/50);
        NSLog(@"The sum is: %d", i);

        // signal the semaphore
        //dispatch_semaphore_signal(sem);
    });
dispatch_release(queue);

 

当主线程在等待信号量时，操作系统会直接将它挂起，因此不会去死做标志轮询，而能够及时将CPU资源给其它可被调度的线程使用。

 

__block dispatch_semaphore_t sem = dispatch_semaphore_create(0);

  dispatch_queue_t queue = dispatch_queue_create("zenny_chen_firstQueue", nil);
  dispatch_async(queue, ^(void) {
      sleep(2-i/50);
      NSLog(@"The sum is: %d", i);

      // signal the semaphore
      dispatch_semaphore_signal(sem);
  });

  // wait for the semaphore
 dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);

 dispatch_release(queue);

2.并发队列 ：Concurrent Queues

dispatch_queue_t aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_queue_t aHQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_queue_t aLQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);

 

 

3.主队列：main dispatch Queue

dispatch_queue_t mainQueue = dispatch_get_main_queue();

针对以上3种队列：concurrent queues和main queue都是由系统生成而且 dispatch_suspend, dispatch_resume, dispatch_set_context这些函数对他们无效。

 

但是我们的应用不是简单的同步也异步的运行，应用经常是混合的。

比如我们要task1 task2 task3都运行完成后才能异步运行task4 task5 task6我们该怎么做呢？这里我们可以引入group的概念。

 

 

-(void)sixthMethod{
    //获取concurrent queue
    dispatch_queue_t aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //创建1个queue group
    dispatch_group_t queueGroup = dispatch_group_create();
    //任务1
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 1.");
    });
    //任务2
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 2.");
    });
    //任务3
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 3.");
    });
    NSLog(@"wait task 1,2,3.");
    //等待组内任务全部完成
    dispatch_group_wait(queueGroup, DISPATCH_TIME_FOREVER);
    NSLog(@"task 1,2,3 finished.");
    //释放组
    dispatch_release(queueGroup);
    //重新创建组
    queueGroup = dispatch_group_create();
    //任务4
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 4.");
    });
    //任务5
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 5.");
    });
    //任务6
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 6.");
    });
    NSLog(@"wait task 4,5,6.");
    //等待组内任务全部完成
    dispatch_group_wait(queueGroup, DISPATCH_TIME_FOREVER);
    NSLog(@"task 4,5,6 finished.");
    //释放组
    dispatch_release(queueGroup);
}

 

 

代码运行结果：

 

2013-05-13 13:55:33.783 GDC[2466:1303] task 1.
2013-05-13 13:55:33.783 GDC[2466:3a07] task 3.
2013-05-13 13:55:33.783 GDC[2466:c07] wait task 1,2,3.
2013-05-13 13:55:33.783 GDC[2466:1903] task 2.
2013-05-13 13:55:33.787 GDC[2466:c07] task 1,2,3 finished.
2013-05-13 13:55:33.788 GDC[2466:c07] wait task 4,5,6.
2013-05-13 13:55:33.788 GDC[2466:1303] task 4.
2013-05-13 13:55:33.788 GDC[2466:1903] task 5.
2013-05-13 13:55:33.788 GDC[2466:3a07] task 6.
2013-05-13 13:55:33.790 GDC[2466:c07] task 4,5,6 finished.