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