linux下条件变量使用总结分析

 1 #include <iostream>
 2 #include <pthread.h>
 3 #include <unistd.h>
 4 #include <stdio.h>
 5 
 6 pthread_mutex_t mutex;
 7 pthread_cond_t cond;
 8 
 9 int g_nums=0;//如果没有这个计数，条件信号会有部分丢失，即在wait之前发的信号都会丢失
10 
11 void* thread1( void* arg)
12 {
13     while(1)
14     {
15 
16         pthread_mutex_lock(&mutex);
17 
18         if(g_nums <=0 )
19             pthread_cond_wait(&cond, &mutex);
20 
21         //sleep(2);
22         if(g_nums <=0 ){//防止惊群现象，wait后再次lock但另一个线程已经用光了资源，如果不检查就使用会出问题
23             std::cout<<"the thread1 conflict..n";
24             continue;
25         }
26 
27         --g_nums;
28 
29         std::cout<<"the thread1 info: "<<std::endl;
30     
31         pthread_mutex_unlock(&mutex);    
32         sleep(1);
33     }
34 
35     return NULL;
36 }
37 
38 void* thread2(void* arg)
39 {
40 
41     while(true){
42         pthread_mutex_lock(&mutex);
43        
44         if(g_nums <=0)
45             pthread_cond_wait(&cond, &mutex);
46 
47         if(g_nums <= 0){//防止惊群现象，wait后再次lock但另一个线程已经用光了资源，如果不检查就使用会出问题
48             std::cout<<"thread2 conflict...n";
49             continue;
50         }
51         --g_nums;
52 
53         std::cout<<"the thread2 info: "<<std::endl;
54 
55         pthread_mutex_unlock(&mutex);
56 
57         sleep(1);
58     }
59 
60     return NULL;
61 }
62 
63 
64 int main( int argc, char*argv[] )
65 {
66     pthread_t t1,t2;
67 
68     pthread_mutex_init(&mutex, NULL);
69 
70     pthread_cond_init(&cond, NULL);
71 
72     pthread_create(&t1, NULL, thread1, NULL);
73     pthread_create(&t2, NULL, thread2, NULL);
74 
75     //sleep(3);
76 
77     for(size_t i=0; i<1; ++i)
78     {
79         //when send a signal to a cond, if no thread is waiting for this cond, so the signal will lost.
80        
81         pthread_mutex_lock(&mutex);
82         ++g_nums;
83         pthread_cond_signal(&cond);
84         pthread_mutex_unlock(&mutex);
85 
86         //sleep(1);
87     }
88 
89     std::cout<<"Please input the Enter to quit.n";
90     getchar();//sleep(10);
91 
92     return 0;
93 }