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.