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 ;

 }

　　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] == ) {

             NSLog(@"wait for products");

             [condition wait];

         }

         [products removeObjectAtIndex:];

         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