NSConditionLock

一、NSConditionLock定义了一个可以指定条件的互斥锁，用于线程之间的互斥与同步。

　　这里的条件并不是bool表达式中的条件，而是一个特定的int值。

二、NSConditionLock的API

　　NSConditionLock实现了NSLocking协议，有lock和unlock方法。

　　NSConditionLock具有以下方法：

- (void)lockWhenCondition:(NSInteger)condition;
 
- (BOOL)tryLock;
 
- (BOOL)tryLockWhenCondition:(NSInteger)condition;
 
- (void)unlockWithCondition:(NSInteger)condition;
 
- (BOOL)lockBeforeDate:(NSDate *)limit;
 
- (BOOL)lockWhenCondition:(NSInteger)condition beforeDate:(NSDate *)limit;

　　lockWhenCondition ：用于condition等于特定值的时候加锁，会阻塞当前线程。

　　tryLock，tryLockWhenCondition ：尝试加锁，加锁失败时返回NO，try开头的方法会理解解锁。

　　lockBeforeDate，lockWhenCondition：指定条件加锁，会阻塞当前线程。

　　unlockWithCondition：指定条件时解锁，每次解锁会导致内部的condition值改变为指定的值，同时唤醒其它阻塞的线程检测这里的condition是否满足条件，因此NSConditionLock相对于NSCondition效率更低。

三、demo

　　接上一节中的main方法，修改NSConditionSample：

@interface NSConditionSample ()
{
    NSConditionLock *conditionLock;
    NSMutableArray *products;
}
 
@end
 
 
@implementation NSConditionSample
 
- (instancetype)init
{
    if(self = [super init])
    {
        conditionLock = [[NSConditionLock alloc] initWithCondition:0];
        products = [[NSMutableArray alloc] init];
    }
    return self;
}
 
 
- (void)createConsumenr
{
    while (YES) {
        NSLog(@"createConsumenr before lock");
        [conditionLock lockWhenCondition:10];
        NSLog(@"createConsumenr after lock");
        if([products count] > 0)
            [products removeObjectAtIndex:0];
        NSLog(@"comsume a product,left %d products",[products count]);
        [conditionLock unlockWithCondition:[products count]==0?0:10];
    }
}
 
- (void)createProducter
{
    while (YES) {
        NSLog(@"createProducter before lock");
        [conditionLock lock];
        NSLog(@"createProducter after lock");
        [products addObject:[[NSObject alloc] init]];
        NSLog(@"produce a product,left %d products",[products count]);
        [conditionLock unlockWithCondition:[products count]];
    }
 
}
 
@end

　　执行结果：

2015-07-24 13:06:31.323 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.323 NSConditionSample[47237:41183763] createConsumenr before lock

2015-07-24 13:06:31.323 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.323 NSConditionSample[47237:41183762] produce a product,left 1 products

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] produce a product,left 2 products

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] produce a product,left 3 products

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] produce a product,left 4 products

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.324 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.325 NSConditionSample[47237:41183762] produce a product,left 5 products

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] produce a product,left 6 products

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] produce a product,left 7 products

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] produce a product,left 8 products

2015-07-24 13:06:31.336 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] produce a product,left 9 products

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] produce a product,left 10 products

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183763] createConsumenr after lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183763] comsume a product,left 9 products

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183763] createConsumenr before lock

2015-07-24 13:06:31.337 NSConditionSample[47237:41183762] produce a product,left 10 products

2015-07-24 13:06:31.338 NSConditionSample[47237:41183762] createProducter before lock

2015-07-24 13:06:31.338 NSConditionSample[47237:41183763] createConsumenr after lock

2015-07-24 13:06:31.338 NSConditionSample[47237:41183763] comsume a product,left 9 products

2015-07-24 13:06:31.338 NSConditionSample[47237:41183763] createConsumenr before lock

2015-07-24 13:06:31.338 NSConditionSample[47237:41183762] createProducter after lock

2015-07-24 13:06:31.338 NSConditionSample[47237:41183762] produce a product,left 10 products