iOS 多线程处理之栅栏函数和依赖(NSoperationQueue,GCD)

1，NSoperationQueue处理A,B,C三个线程，要求执行完A,B后才能执行C。

添加依赖关系，代码：

- (void)operation {
    
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    
    NSBlockOperation *A = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"A----%@",[NSThread currentThread]);
    }];
    
    NSBlockOperation *B = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"B---%@",[NSThread currentThread]);
    }];
    
    NSBlockOperation *C = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"C---%@",[NSThread currentThread]);
    }];
    
    [C addDependency:A];
    [C addDependency:B];
    
    [queue addOperation:A];
    [queue addOperation:B];
    [queue addOperation:C];
    
}

2，使用GCD的栅栏函数或者队列组

- (void)combineImages {
    /*
     1,开启两个线程处理A和B
     2,通过任务组执行A,B之后执行C
     */
    dispatch_queue_t queue = dispatch_queue_create("dealWith", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_async(group, queue, ^{
        NSLog(@"A----%@",[NSThread currentThread]);
    });
    
    dispatch_group_async(group, queue, ^{
        NSLog(@"B---%@",[NSThread currentThread]);
    });
    
    dispatch_group_notify(group, queue, ^{
        NSLog(@"C---%@",[NSThread currentThread]);
    });
    
}

3,GCD添加栅栏函数

- (void)GCDasyn {
    
    //栅栏函数（栅栏函数不能用全局并发队列）
    //等执行完栅栏函数中的代码蔡继续执行下面的代码
    
    dispatch_queue_t queue = dispatch_queue_create("dealWith", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_barrier_async(queue, ^{
        NSLog(@"A----%@",[NSThread currentThread]);
    });
    
    dispatch_barrier_async(queue, ^{
        NSLog(@"B---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"C---%@",[NSThread currentThread]);
    });
    
}