GCD代码记录，以便后用

//自定义一个queue：
- (void)customQueue{
    /*
     第二个参数传：
     串行队列：DISPATCH_QUEUE_SERIAL     开启一个子线程，按序执行
     并行队列：DISPATCH_QUEUE_CONCURRENT 开启多个子线程，无序执行
     同步：串行、并行都会在主线程
     异步：串行、并行都会在子线程
     */
    
    //串行队列
    dispatch_queue_t serialQueue = dispatch_queue_create("com.gcd.serialQueue", DISPATCH_QUEUE_SERIAL);
    //并发队列
    dispatch_queue_t concurrentQueue = dispatch_queue_create("com.gcd.concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
    
//可以通过dispatch_queue_get_label(dispatch_queue_t queue)获取你创建queue的名字
    const char *c = dispatch_queue_get_label(concurrentQueue);
    NSLog(@"%s",c);//com.gcd.concurrentQueue

    dispatch_sync(concurrentQueue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"1--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"2--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:4];
        NSLog(@"3--");
    });
    dispatch_sync(concurrentQueue, ^{
        NSLog(@"4");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"4--");
    });
}

dispatch_group

/*
 串行队列：DISPATCH_QUEUE_SERIAL     开启一个子线程，按序执行
 并行队列：DISPATCH_QUEUE_CONCURRENT 开启多个子线程，无序执行
 */
- (void)dispatch_group{
    dispatch_queue_t queue = dispatch_queue_create("com.gcd.serialQueue", DISPATCH_QUEUE_SERIAL);
    dispatch_group_t group = dispatch_group_create();

    dispatch_group_async(group, queue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"1--");
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:8];
        NSLog(@"2--");
    });
    dispatch_group_async(group, queue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"3--");
    });

    dispatch_group_notify(group, queue, ^{
        NSLog(@"notify：任务都完成了");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"回到主线程");
        });
    });
}

dispatch_group_enter和dispatch_group_leave是成对出现的，可以按照引用计数+1、-1理解。

/*
 串行队列：DISPATCH_QUEUE_SERIAL     开启一个子线程，按序执行
 并行队列：DISPATCH_QUEUE_CONCURRENT 开启多个子线程，无序执行
 注意：dispatch_group_notify会与耗时最长的线程在同一个线程
 */
- (void)dispatch_group_enter{
    dispatch_queue_t queue = dispatch_queue_create("com.GCD.group", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(5);
        NSLog(@"任务一完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(8);
        NSLog(@"任务二完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(queue, ^{
        sleep(3);
        NSLog(@"任务三完成");
        dispatch_group_leave(group);
    });
    
    dispatch_group_notify(group, queue, ^{
        NSLog(@"任务完成");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"回到主线程");
        });
    });
}

dispatch_barrier

/*
 dispatch_barrier_sync和dispatch_barrier_async的共同点：
 1、都会等待在它前面插入队列的任务（1、2、3）先执行完
 2、都会等待他们自己的任务（0）执行完再执行后面的任务（4、5、6）
 
 dispatch_barrier_sync和dispatch_barrier_async的不共同点：
 在将任务插入到queue的时候，dispatch_barrier_sync需要等待自己的任务（0）结束之后才会继续程序，然后插入被写在它后面的任务（4、5、6），然后执行后面的任务
 而dispatch_barrier_async将自己的任务（0）插入到queue之后，不会等待自己的任务结束，它会继续把后面的任务（4、5、6）插入到queue
 */
- (void)dispatch_barrier{
    dispatch_queue_t queue = dispatch_queue_create("com.GCD.barrier", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"1");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"1--");
    });
    dispatch_async(queue, ^{
        NSLog(@"2");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"2--");
    });
    dispatch_async(queue, ^{
        NSLog(@"3");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"3--");
    });
    
    dispatch_barrier_async(queue, ^{
        NSLog(@"barrier");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"barrier--");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"barrier==");
    });
    NSLog(@"aaa");
    dispatch_async(queue, ^{
        NSLog(@"4");
        [NSThread sleepForTimeInterval:3];
        NSLog(@"4--");
    });
    NSLog(@"bbb");
    dispatch_async(queue, ^{
        NSLog(@"5");
        [NSThread sleepForTimeInterval:5];
        NSLog(@"5--");
    });
    dispatch_async(queue, ^{
        NSLog(@"6");
        [NSThread sleepForTimeInterval:2];
        NSLog(@"6--");
    });
}