GCD 串行隊列,併發隊列和主隊列的整理

1.串行隊列：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);

 

 

異步

 

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);

 

當主線程在等待信號量時，操做系統會直接將它掛起，所以不會去死作標誌輪詢，而可以及時將CPU資源給其它可被調度的線程使用。

 

__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.併發隊列 ：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.主隊列：main dispatch Queue

dispatch_queue_t mainQueue = dispatch_get_main_queue();

針對以上3種隊列：concurrent queues和main queue都是由系統生成並且 dispatch_suspend, dispatch_resume, dispatch_set_context這些函數對他們無效。

 

可是咱們的應用不是簡單的同步也異步的運行，應用常常是混合的。

好比咱們要task1 task2 task3都運行完成後才能異步運行task4 task5 task6咱們該怎麼作呢？這裏咱們能夠引入group的概念。

 

 

-(void)sixthMethod{
    //獲取concurrent queue
    dispatch_queue_t aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //建立1個queue group
    dispatch_group_t queueGroup = dispatch_group_create();
    //任務1
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 1.");
    });
    //任務2
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 2.");
    });
    //任務3
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 3.");
    });
    NSLog(@"wait task 1,2,3.");
    //等待組內任務所有完成
    dispatch_group_wait(queueGroup, DISPATCH_TIME_FOREVER);
    NSLog(@"task 1,2,3 finished.");
    //釋放組
    dispatch_release(queueGroup);
    //從新建立組
    queueGroup = dispatch_group_create();
    //任務4
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 4.");
    });
    //任務5
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 5.");
    });
    //任務6
    dispatch_group_async(queueGroup, aQueue, ^{
        NSLog(@"task 6.");
    });
    NSLog(@"wait task 4,5,6.");
    //等待組內任務所有完成
    dispatch_group_wait(queueGroup, DISPATCH_TIME_FOREVER);
    NSLog(@"task 4,5,6 finished.");
    //釋放組
    dispatch_release(queueGroup);
}

 

 

代碼運行結果：

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.