参考文档

参考文档中一共提到8种锁，讲解的很详细。后续可以抽空继续学习。暂且就其中的两种锁作一简单记录：

NSLock:

  //主线程中
    NSLock *lock = [[NSLock alloc] init];
 
    //线程1
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lock];
        NSLog(@"线程1");
        sleep(2);
        NSLog(@"线程1解锁成功");
        [lock unlock];
    });
 
    //线程2
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lock];
        NSLog(@"线程2");
        sleep(1);
        NSLog(@"线程2解锁成功");
        [lock unlock];
    });

NSConditionLock

    //主线程中
    NSConditionLock *lock = [[NSConditionLock alloc] initWithCondition:0];
    
    //线程1
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lockWhenCondition:4];
        NSLog(@"线程1");
        sleep(2);
        [lock unlockWithCondition:5];
    });
    
    //线程2
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lockWhenCondition:0];
        NSLog(@"线程2");
        sleep(3);
        NSLog(@"线程2解锁成功");
        [lock unlockWithCondition:2];
    });
    
    //线程3
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lockWhenCondition:2];
        NSLog(@"线程3");
        sleep(3);
        NSLog(@"线程3解锁成功");
        [lock unlockWithCondition:3];
    });
    
    //线程4
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [lock lockWhenCondition:3];
        NSLog(@"线程4");
        sleep(2);
        NSLog(@"线程4解锁成功");
        [lock unlockWithCondition:4];
    });

锁是一种常用的同步工具。从代码的角度讲就是加锁时，同一时刻只能有一个锁内代码执行。也可以用来做添加线程依赖。但实测，在网络请求的线程处理时还是得细心处理。