ios激情详解之GCD

    @interface ViewController ()  
    {  
        int _totalCount; // 火车票总票数  
        int _surplusCount; // 剩余票数  
        NSLock *_lock; // 互斥锁  
    }  
      
    @end  


[objc] view plaincopy

    // 设置剩余票数  
        _surplusCoynt = 100;  
          
        _lock = [[NSLock alloc] init]; // 创建互斥锁，多个线程共享使用  
          
        // 自己创建并行队列  
        dispatch_queue_t queue1 = dispatch_queue_create("火车站", DISPATCH_QUEUE_CONCURRENT);  
        dispatch_async(queue1, ^{  
            [self saleTickets:queue1];  
        });  
          
        dispatch_queue_t queue2 = dispatch_queue_create("代售点", DISPATCH_QUEUE_CONCURRENT);  
        dispatch_async(queue2, ^{  
            [self saleTickets:queue2];  
        });  


[objc] view plaincopy

    #pragma mark - 售票方法  
    - (void)saleTickets:(dispatch_queue_t)queue  
    {  
        while (_surplusCount > 0) {  
            [_lock lock]; // 获取互斥锁并且添加  
            const charchar *queueLabel = dispatch_queue_get_label(queue);  
            NSString *label = [NSString stringWithUTF8String:queueLabel];  
            NSLog(@"当前火车票由%@售出，余票:%d张", label, _surplusCount);  
            _surplusCount--;  
            [_lock unlock];  
        }  
    }