NSCondition

一、NSCondition是对条件变量和互斥量的一个封装，用于线程之间的同步。

　　其中的互斥量用于保护对条件变量的修改，条件变量变化以信号量的方式通知其它线程实现线程之间的同步。

　　

二、NSCondition的API

　　NSCondition实现了NSLocking协议，这个协议定义了lock和unlock方法，用于多个线程互斥得执行一段代码，以保护共享的数据。

　　同时，NSCondition还包含以下方法：

　　- (void)wait;

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

　　- (void)signal;

　　- (void)broadcast;

　　

　　wait：释放互斥量，使当前线程等待，切换到其它线程执行。

　　waitUntilDate：释放互斥量，使当前线程等待到某一个时间，切换到其它线程执行。

　　signal：唤醒一个其它等待该条件变量的线程

　　broadcast：唤醒所有其它等待该条件变量的线程

三、demo

　　下面的例子来源于网络，对其做了一点修改

　　

int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...

NSConditionSample *sample = [[NSConditionSample alloc] init];

[NSThread detachNewThreadSelector:@selector(createConsumenr)
toTarget:sample
withObject:nil];

[NSThread detachNewThreadSelector:@selector(createProducter)
toTarget:sample
withObject:nil];

getchar();
}
return 0;
}

　　下面是生产者、消费者：

#import "NSConditionSample.h"

@interface NSConditionSample ()
{
NSCondition *condition;
NSMutableArray *products;
}

@end

@implementation NSConditionSample

- (instancetype)init
{
if(self = [super init])
{
condition = [[NSCondition alloc] init];
products = [[NSMutableArray alloc] init];
}
return self;
}

- (void)createConsumenr
{
while (YES) {
NSLog(@"createConsumenr before lock");
[condition lock];
NSLog(@"createConsumenr after lock");
while ([products count] == 0) {
NSLog(@"wait for products");
[condition wait];
}
[products removeObjectAtIndex:0];
NSLog(@"comsume a product");
[condition unlock];
}
}

- (void)createProducter
{
while (YES) {
NSLog(@"createProducter before lock");
[condition lock];
NSLog(@"createProducter after lock");
[products addObject:[[NSObject alloc] init]];
NSLog(@"produce a product");
[condition signal];
[condition unlock];
}

}

@end

执行的log：

2015-07-24 11:05:48.374 NSConditionSample[45259:40628634] createConsumenr before lock

2015-07-24 11:05:48.374 NSConditionSample[45259:40628635] createProducter before lock

2015-07-24 11:05:48.374 NSConditionSample[45259:40628634] createConsumenr after lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628634] wait for products

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] createProducter after lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] produce a product

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] createProducter before lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628634] comsume a product

2015-07-24 11:05:48.375 NSConditionSample[45259:40628634] createConsumenr before lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] createProducter after lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] produce a product

2015-07-24 11:05:48.375 NSConditionSample[45259:40628634] createConsumenr after lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628635] createProducter before lock

2015-07-24 11:05:48.375 NSConditionSample[45259:40628634] comsume a product

2015-07-24 11:05:48.376 NSConditionSample[45259:40628634] createConsumenr before lock

2015-07-24 11:05:48.376 NSConditionSample[45259:40628635] createProducter after lock

2015-07-24 11:05:48.376 NSConditionSample[45259:40628635] produce a product

2015-07-24 11:05:48.376 NSConditionSample[45259:40628634] createConsumenr after lock

2015-07-24 11:05:48.376 NSConditionSample[45259:40628635] createProducter before lock

2015-07-24 11:05:48.376 NSConditionSample[45259:40628634] comsume a product

2015-07-24 11:05:48.390 NSConditionSample[45259:40628634] createConsumenr before lock

2015-07-24 11:05:48.390 NSConditionSample[45259:40628635] createProducter after lock

2015-07-24 11:05:48.390 NSConditionSample[45259:40628635] produce a product