iOS开发中常用的锁有如下几种

来比较一下遇到加锁的情况：

1. @synchronized 关键字加锁

2. NSLock 对象锁 
3. NSCondition  
4. NSConditionLock 条件锁 
5. NSRecursiveLock 递归锁 
6. pthread_mutex 互斥锁（C语言） 
7. dispatch_semaphore 信号量实现加锁（GCD）

8. OSSpinLock （暂不建议使用，原因参见这里）

//分别使用8种方式加锁 解锁1千万次

- (void)runLock{

CFTimeInterval timeBefore;

CFTimeInterval timeCurrent;

NSUInteger i;

NSUInteger count = 1000*10000;//执行一千万次

//@synchronized

id obj = [[NSObjectalloc]init];;

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

@synchronized(obj){

}

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("@synchronized used : %f\n", timeCurrent-timeBefore);

//NSLock

NSLock *lock = [[NSLockalloc]init];

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

[lock lock];

[lock unlock];

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("NSLock used : %f\n", timeCurrent-timeBefore);

//NSCondition

NSCondition *condition = [[NSConditionalloc]init];

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

[condition lock];

[condition unlock];

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("NSCondition used : %f\n", timeCurrent-timeBefore);

//NSConditionLock

NSConditionLock *conditionLock = [[NSConditionLockalloc]init];

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

[conditionLock lock];

[conditionLock unlock];

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("NSConditionLock used : %f\n", timeCurrent-timeBefore);

//NSRecursiveLock

NSRecursiveLock *recursiveLock = [[NSRecursiveLockalloc]init];

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

[recursiveLock lock];

[recursiveLock unlock];

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("NSRecursiveLock used : %f\n", timeCurrent-timeBefore);

//pthread_mutex

pthread_mutex_t mutex =PTHREAD_MUTEX_INITIALIZER;

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

pthread_mutex_lock(&mutex);

pthread_mutex_unlock(&mutex);

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("pthread_mutex used : %f\n", timeCurrent-timeBefore);

//dispatch_semaphore

dispatch_semaphore_t semaphore =dispatch_semaphore_create(1);

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

dispatch_semaphore_wait(semaphore,DISPATCH_TIME_FOREVER);

dispatch_semaphore_signal(semaphore);

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("dispatch_semaphore used : %f\n", timeCurrent-timeBefore);

//OSSpinLockLock

OSSpinLock spinlock = OS_SPINLOCK_INIT;

timeBefore = CFAbsoluteTimeGetCurrent();

for(i=0; i<count; i++){

OSSpinLockLock(&spinlock);

OSSpinLockUnlock(&spinlock);

}

timeCurrent = CFAbsoluteTimeGetCurrent();

printf("OSSpinLock used : %f\n", timeCurrent-timeBefore);

}

输出结果如下：

由图可以发现：
OSSpinLock的性能最好（不建议使用），GCD的dispatch_semaphore紧随其后； 
NSConditionLock和@synchronized性能较差；

注意： 
1. 需要注意的是这里仅仅是对各种锁直接Lock和Unlock的性能测试，其中部分锁的使用条件上还是有细微的差异的，比如NSLock之类的还有tryLock等方法用于加锁，不同对象锁的功能偏向不一样等等，有兴趣的可以逐个搜索再更深入的研究不同锁之间的区别。 
2. 另外，一般来说客户端很少会有这么大量的加锁解锁操作，所以日常来说这些锁的性能都是可以满足使用需求的。