Linux多线程编程 - sleep 和 pthread_cond_timedwait

Posted 2020-10-03 _小百

#include <stdio.h>

#include <stdlib.h>

int flag = 1;

void * thr_fn(void * arg)

{  

while (flag)

{    

printf("******\\n");    

sleep(10);  

}  

printf("sleep test thread exit\\n");

}  

int main()

{  

pthread_t thread;  

if (0 != pthread_create(&thread, NULL, thr_fn, NULL))

{    

printf("error when create pthread,%d\\n", errno);    

return 1;  

}    

char c ;  

while ((c = getchar()) != \'q\');    

printf("Now terminate the thread!\\n");  

flag = 0;  

printf("Wait for thread to exit\\n");  

pthread_join(thread, NULL);  

printf("Bye\\n");   return 0;

}

输入q后，需要等线程从sleep中醒来（由挂起状态变为运行状态），即最坏情况要等10s，线程才会被join。采用sleep的缺点：不能及时唤醒线程。

 

采用pthread_cond_timedwait函数，条件到了，线程即会被join，可及时唤醒线程。实现的如下：

#include <stdio.h> #include <sys/time.h> #include <unistd.h> #include <pthread.h> #include <errno.h>   static pthread_t thread; static pthread_cond_t cond; static pthread_mutex_t mutex; static int flag = 1;   void * thr_fn(void * arg) {   struct timeval now;   struct timespec outtime;   pthread_mutex_lock(&mutex);   while (flag) {     printf("*****\\n");     gettimeofday(&now, NULL);     outtime.tv_sec = now.tv_sec + 5;     outtime.tv_nsec = now.tv_usec * 1000;     pthread_cond_timedwait(&cond, &mutex, &outtime);   }   pthread_mutex_unlock(&mutex);   printf("cond thread exit\\n"); }   int main(void) {   pthread_mutex_init(&mutex, NULL);   pthread_cond_init(&cond, NULL);   if (0 != pthread_create(&thread, NULL, thr_fn, NULL)) {     printf("error when create pthread,%d\\n", errno);     return 1;   }   char c ;   while ((c = getchar()) != \'q\');   printf("Now terminate the thread!\\n"); pthread_mutex_lock(&mutex);   flag = 0;   pthread_cond_signal(&cond);   pthread_mutex_unlock(&mutex);   printf("Wait for thread to exit\\n");   pthread_join(thread, NULL);   printf("Bye\\n");   return 0; }

pthread_cond_timedwait()函数阻塞住调用该函数的线程，等待由cond指定的条件被触发（pthread_cond_broadcast() or pthread_cond_signal()）。

　　当pthread_cond_timedwait()被调用时，调用线程必须已经锁住了mutex。函数pthread_cond_timedwait()会对mutex进行【解锁和执行对条件的等待】（原子操作）。