GCD排列组合

/**
 *  同步函数　＋　主队列　＝　卡住
 */
- (void)syncMain {

    NSLog(@"syncMain-------begin");

    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"1----%@", [NSThread currentThread]);
    });
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"2----%@", [NSThread currentThread]);
    });
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"3----%@", [NSThread currentThread]);
    });

    NSLog(@"syncMain-------end");
}

/**
 *  异步函数　＋　主队列　＝　不开线程
 *  主队列优先级高于异步函数，所以即使是异步函数，同样不创建线程
 */
- (void)asyncMain {
    dispatch_async(dispatch_get_main_queue(), ^{
         NSLog(@"1----%@", [NSThread currentThread]);
    });
    dispatch_async(dispatch_get_main_queue(), ^{
         NSLog(@"2----%@", [NSThread currentThread]);
    });
    dispatch_async(dispatch_get_main_queue(), ^{
         NSLog(@"3----%@", [NSThread currentThread]);
    });
}

/**
 *  异步函数　＋　并发队列　＝　开启多条线程，由于并发，会开启多条线程
 */
- (void)asyncConcurrent {
    // 全局队列都是并发队列
    dispatch_queue_t queue =                dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 10; i++) {
            NSLog(@"1----%@", [NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 10; i++) {
            NSLog(@"2----%@", [NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 10; i++) {
            NSLog(@"3----%@", [NSThread currentThread]);
        }
     });
}

/**
 *  异步函数　＋　串行队列　＝　可以开启条线程，但是只会开一条
 */
- (void)asyncSerial {
    dispatch_queue_t queue = dispatch_queue_create("com.guoqi.queue", NULL);

    dispatch_async(queue, ^{
        NSLog(@"1----%@", [NSThread currentThread]);
    });

    dispatch_async(queue, ^{
        NSLog(@"2----%@", [NSThread currentThread]);
    });

    dispatch_async(queue, ^{
        NSLog(@"3----%@", [NSThread currentThread]);
    });
}

/**
 *  同步函数　＋　串行队列　＝　不开线程，顺序执行
 */
- (void)syncSerial {
    dispatch_queue_t queue = dispatch_queue_create("com.guoqi.queue", NULL);

    dispatch_sync(queue, ^{
        NSLog(@"1----%@", [NSThread currentThread]);
    });

    dispatch_sync(queue, ^{
        NSLog(@"2----%@", [NSThread currentThread]);
    });

    dispatch_sync(queue, ^{
        NSLog(@"3----%@", [NSThread currentThread]);
    });
}

/**
 *  同步函数　＋　并发队列　＝　不开线程，顺序执行
 */
- (void)syncConcurrent {
    dispatch_queue_t queue =     dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_sync(queue, ^{
        NSLog(@"1----%@", [NSThread currentThread]);
    });

    dispatch_sync(queue, ^{
        NSLog(@"2----%@", [NSThread currentThread]);
    });

    dispatch_sync(queue, ^{
        NSLog(@"3----%@", [NSThread currentThread]);
    });
}