iOS锁系列-NSConditionLock条件锁

@interface NSConditionLock : NSObject <NSLocking> {
@private
    void *_priv;
}
//初始化一个NSConditionLock对象
- (instancetype)initWithCondition:(NSInteger)condition NS_DESIGNATED_INITIALIZER;

@property (readonly) NSInteger condition;  //锁的条件

//满足条件时加锁
- (void)lockWhenCondition:(NSInteger)condition;


- (BOOL)tryLock;
//如果接收对象的condition与给定的condition相等，则尝试获取锁，不阻塞线程
- (BOOL)tryLockWhenCondition:(NSInteger)condition;

//解锁后，重置锁的条件
- (void)unlockWithCondition:(NSInteger)condition;

- (BOOL)lockBeforeDate:(NSDate *)limit;

//在指定时间前尝试获取锁，若成功则返回YES 否则返回NO
- (BOOL)lockWhenCondition:(NSInteger)condition beforeDate:(NSDate *)limit;

@property (nullable, copy) NSString *name API_AVAILABLE(macos(10.5), ios(2.0), watchos(2.0), tvos(9.0));

@end

代码示例：

    //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:1];
        NSLog(@"线程1");
        sleep(2);
        [lock unlock];
    });
    
    //线程2
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        sleep(1);//以保证让线程2的代码后执行
        if ([lock tryLockWhenCondition:0]) {
            NSLog(@"线程2");
            [lock unlockWithCondition:2];
            NSLog(@"线程2解锁成功");
        }
        else {
            NSLog(@"线程2尝试加锁失败");
        }
    });
    
    //线程3
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
       // sleep(2);//以保证让线程2的代码后执行
        if ([lock tryLockWhenCondition:2]) {
            NSLog(@"线程3");
            [lock unlock];
            NSLog(@"线程3解锁成功");
        }
        else {
            NSLog(@"线程3尝试加锁失败");
        }
    });
    
    //线程4
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
       // sleep(3);//以保证让线程2的代码后执行
        
        [lock lockWhenCondition:2];
        NSLog(@"线程4");
        [lock unlockWithCondition:1];
        NSLog(@"线程4解锁成功");
        
    });

打印结果：

2018-04-17 16:59:26.995255+0800 NSLock测试[48379:5945905] 线程3尝试加锁失败
2018-04-17 16:59:28.000120+0800 NSLock测试[48379:5945903] 线程2
2018-04-17 16:59:28.000791+0800 NSLock测试[48379:5945903] 线程2解锁成功
2018-04-17 16:59:28.000851+0800 NSLock测试[48379:5945904] 线程4
2018-04-17 16:59:28.001999+0800 NSLock测试[48379:5945904] 线程4解锁成功
2018-04-17 16:59:28.002044+0800 NSLock测试[48379:5945902] 线程1

结果说明：

1 初始化一个条件锁，条件为0
2 由于线程1 和线程4条件不满足，所以循环一段时间休眠，等待满足条件满足时唤醒；线程3尝试加锁，不会阻塞线程，但是条件不满足所以直接休眠；线程2休眠1秒后尝试加锁。满足条件所以加锁成功；
3 线程2伴随重置加锁条件2进行解锁；
4 此时线程4满足条件，系统唤醒进行加锁，并且重置加锁条件14
5 此时线程1满足条件，系统唤醒进行加锁，并且解锁，此时条件为1