Linux多线程编程 - sleep 和 pthread_cond_timedwait

 

#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）。