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 ", 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 ", 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 ", 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 ", 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 ", 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 ", 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 ", 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 ", 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。