NSCondition和NSConditionLock

NSCondition

@interface NSCondition :NSObject <NSLocking> {

@private

   void *_priv;

}

- (void)wait;//挂起线程

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

- (void)signal; //任意通知一个线程

- (void)broadcast; //通知所有等待的线程

@property (nullable,copy)NSString *nameNS_AVAILABLE(10_5,2_0);

@end

类似GCD的信号量，wait之后当前线程会被阻塞直到 lock signal。
在用的时候注意，首先对lock对象进行lock.

举例：

-(void)threadMethod:(NSCondition*)lock{

    [locklock];

    [lockwait];

    [lockunlock];

}

发布的时候：

[locklock];

                [lockbroadcast];

                [lockunlock];

代码演示：

- (void)executeLock {    NSCondition* lock = [[NSCondition alloc] init];    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        for (NSUInteger i=0; i<3; i++) {            sleep(2);            if (i == 2) {                [lock lock];                [lock broadcast];                [lock unlock];            }                    }    });            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        sleep(1);        [self threadMethod:lock];    });            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        sleep(1);        [self threadMethod:lock];    });    }-(void)threadMethod:(NSCondition*)lock{    [lock lock];    [lock wait];    [lock unlock];}

NSCondition实现了NSLocking协议，当多个线程访问同一段代码时，会以wait为分水岭。一个线程等待另一个线程unlock之后，在走wait之后的代码。

NSConditionLock:

@interface NSConditionLock :NSObject <NSLocking> {

@private

   void *_priv;

}

- (instancetype)initWithCondition:(NSInteger)conditionNS_DESIGNATED_INITIALIZER;

@property (readonly)NSInteger condition; //这属性非常重要，外部传入的condition与之相同才会获取到lock对象，反之阻塞当前线程，直到condition相同

- (void)lockWhenCondition:(NSInteger)condition; //condition与内部相同才会获取锁对象并立即返回，否则阻塞线程直到condition相同

- (BOOL)tryLock;//尝试获取锁对象，获取成功需要配对unlock

- (BOOL)tryLockWhenCondition:(NSInteger)condition; //同上

- (void)unlockWithCondition:(NSInteger)condition; //解锁，并且设置lock.condition = condition

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

- (BOOL)lockWhenCondition:(NSInteger)condition beforeDate:(NSDate *)limit;

@property (nullable,copy)NSString *nameNS_AVAILABLE(10_5,2_0);

@end

代码实例：

- (void)executeLock {    NSConditionLock* lock = [[NSConditionLock alloc] init];    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        for (NSUInteger i=0; i<3; i++) {            sleep(2);            if (i == 2) {                [lock lock];                [lock unlockWithCondition:i];            }                    }    });            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        sleep(1);        [self threadMethod:lock];    });            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        sleep(1);        [self threadMethod:lock];    });    }-(void)threadMethod:(NSConditionLock*)lock{    [lock lockWhenCondition:2];    [lock unlock];}

NSConditionLock实现了NSLocking协议，一个线程会等待另一个线程unlock或者unlockWithCondition:之后再走lock或者lockWhenCondition:之后的代码。