《iOS多线程简介》中提到：GCD中有2个核心概念：1、任务（执行什么操作）2、队列（用来存放任务）

那么多线程GCD的基本使用有哪些呢？

可以分以下多种情况：

1、异步函数 + 并发队列

/**
 * 异步函数 + 并发队列：可以同时开启多条线程
 */
- (void)asyncConcurrent
{
    // 1.创建一个并发队列
    // dispatch_queue_create(const char *label, dispatch_queue_attr_t attr);
    // label : 相当于队列的名字
    // dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_CONCURRENT);
    
    // 1.获得全局的并发队列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 2.将任务加入队列
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is first %@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is second %@",[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i<3; i++) {
            NSLog(@"this is third %@",[NSThread currentThread]);
        }
    });
    
}

2、同步函数 + 并发队列

/**
 * 同步函数 + 并发队列：不会开启新的线程
 */

- (void)syncConcurrent
{
    // 1.获得全局的并发队列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 2.将任务加入队列
    dispatch_sync(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
    
}

3、异步函数 + 串行队列

/**
 * 异步函数 + 串行队列：会开启新的线程，但是任务是串行的，执行完一个任务，再执行下一个任务
 */
- (void)asyncSerial
{
    // 1.创建串行队列
    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_SERIAL);
    //    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", NULL);
    
    // 2.将任务加入队列
    dispatch_async(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

4、同步函数 + 串行队列

/**
 * 同步函数 + 串行队列：不会开启新的线程，在当前线程执行任务。任务是串行的，执行完一个任务，再执行下一个任务
 */
- (void)syncSerial
{
    // 1.创建串行队列
    dispatch_queue_t queue = dispatch_queue_create("com.kyle.queue", DISPATCH_QUEUE_SERIAL);
    
    // 2.将任务加入队列
    dispatch_sync(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is second %@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

5、异步函数 + 主队列

// * 异步函数 + 主队列：只在主线程中执行任务

- (void)asyncMain
{
    // 1.获得主队列
    dispatch_queue_t  queue =  dispatch_get_main_queue();
    // 2.将任务加入队列
    dispatch_async(queue, ^{
        NSLog(@"this is first %@",[NSThread currentThread]);
        NSLog(@"this is second %@",[NSThread currentThread]);
        NSLog(@"this is third %@",[NSThread currentThread]);
    });
}

6、同步函数 + 主队列

// * 同步函数 + 主队列：
- (void)syncMain
{
    NSLog(@"begin");
    
    // 1.获得主队列
    dispatch_queue_t queue =  dispatch_get_main_queue();
    // 2.将任务加入队列
    dispatch_sync(queue, ^{
        NSLog(@"this is %@",[NSThread currentThread]);
        
    });
    NSLog(@"end");
}

造成“相互等待的