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

 1 int main(int argc, const char * argv[]) {
 2     @autoreleasepool {
 3         // insert code here...
 4         
 5         NSConditionSample *sample = [[NSConditionSample alloc] init];
 6         
 7         [NSThread detachNewThreadSelector:@selector(createConsumenr)
 8                                  toTarget:sample
 9                                withObject:nil];
10         
11         [NSThread detachNewThreadSelector:@selector(createProducter)
12                                  toTarget:sample
13                                withObject:nil];
14         
15  
16         
17         
18         
19         
20         
21         getchar();
22     }
23     return 0;
24 }

　　下面是生产者、消费者：

 1 #import "NSConditionSample.h"
 2 
 3 @interface NSConditionSample ()
 4 {
 5     NSCondition *condition;
 6     NSMutableArray *products;
 7 }
 8 
 9 @end
10 
11 
12 @implementation NSConditionSample
13 
14 - (instancetype)init
15 {
16     if(self = [super init])
17     {
18         condition = [[NSCondition alloc] init];
19         products = [[NSMutableArray alloc] init];
20     }
21     return self;
22 }
23 
24 
25 - (void)createConsumenr
26 {
27     while (YES) {
28         NSLog(@"createConsumenr before lock");
29         [condition lock];
30         NSLog(@"createConsumenr after lock");
31         while ([products count] == 0) {
32             NSLog(@"wait for products");
33             [condition wait];
34         }
35         [products removeObjectAtIndex:0];
36         NSLog(@"comsume a product");
37         [condition unlock];
38     }
39 }
40 
41 - (void)createProducter
42 {
43     while (YES) {
44         NSLog(@"createProducter before lock");
45         [condition lock];
46         NSLog(@"createProducter after lock");
47         [products addObject:[[NSObject alloc] init]];
48         NSLog(@"produce a product");
49         [condition signal];
50         [condition unlock];
51     }
52 
53 }
54 
55 @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