GCD

1、同步串行队列

/**
 不会创建新的线程，队列中的任务遵循FIFO
 */
 - (void)syncSerial{

    NSLog(@">>>>>>>>start<<<<<<<<<<<<");
    dispatch_queue_t queue = dispatch_queue_create("downLoading", DISPATCH_QUEUE_SERIAL);
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download1:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download2:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download3:%zd---%@",i,[NSThread currentThread]);
        }
    });
    NSLog(@">>>>>>>>end<<<<<<<<<<<<");
}

2、同步并行队列

/**
 不会创建新的线程，队列中的任务遵循FIFO
 */
- (void)syncConCurrent {

    NSLog(@">>>>>>>>Start<<<<<<<<<<<<");
    dispatch_queue_t queue = dispatch_queue_create("downLoading", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download1:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download2:%zd---%@",i,[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download3:%zd---%@",i,[NSThread currentThread]);
        }
    });
    NSLog(@">>>>>>>>end<<<<<<<<<<<<");
}

3、异步串行队列

/**
 开启一条新线程
 队列中的任务遵循FIFO执行
 */
- (void)ayncSerial {

    NSLog(@">>>>>>>>start<<<<<<<<<<<<");
    dispatch_queue_t queue = dispatch_queue_create("downLoading", DISPATCH_QUEUE_SERIAL);
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download1:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download2:%zd---%@",i,[NSThread currentThread]);
        }
    });

    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download3:%zd---%@",i,[NSThread currentThread]);
        }
    });
     NSLog(@">>>>>>>>end<<<<<<<<<<<<");
}

4、异步并行队列

/**
 异步并行队列 
 开启多条新线程，任务并发执行
 获取全局队列dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
 *  - DISPATCH_QUEUE_PRIORITY_HIGH:
 *  - DISPATCH_QUEUE_PRIORITY_DEFAULT:
 *  - DISPATCH_QUEUE_PRIORITY_LOW:
 *  - DISPATCH_QUEUE_PRIORITY_BACKGROUND:
 第一个参数：队列优先级（2:HIGH  0:DEFAUL -2:LOW INT16_MIN:BACKGROUND:）
 第二个参数：暂时未用到(Reserved for future use)
*/
- (void)ayncConCurrent {

    NSLog(@">>>>>>>>Start<<<<<<<<<<<<");
    //创建方式一：获取全局并发队列
//    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    //创建方式二：
    dispatch_queue_t queue = dispatch_queue_create("downLoading", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download1:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download2:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download3:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    NSLog(@">>>>>>>>end<<<<<<<<<<<<");
}

5、死锁

主线程中创建同步串行队列

- (void)syncLock {

     NSLog(@">>>>>>>>Start<<<<<<<<<<<<");
    dispatch_queue_t queue = dispatch_get_main_queue() ;
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download1:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download2:%zd---%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_sync(queue, ^{
        for (NSInteger i = 0; i < 100; i ++) {
            NSLog(@"download3:%zd---%@",i,[NSThread currentThread]);
        }
    });
    NSLog(@">>>>>>>>end<<<<<<<<<<<<");
}

主线程中直接调用该方法会导致死锁

[self syncLock]

原因：dispatch_sync会阻塞当前线程，然后把block中的任务放到指定的线程中执行，但此时主线程被阻塞，所以block中的任务始终不能完成，导致死锁现象。
解决方法：在主线程中开启新的线程

dispatch_async(dispatch_get_global_queue(0, 0), ^{
    [self syncLock];
 });

死锁.jpg