#include <stdio.h> #include <stdlib.h>
int flag = 1; void * thr_fn(void * arg) { while (flag){ printf("****** "); sleep(10); } printf("sleep test thread exit "); } int main() { pthread_t thread; if (0 != pthread_create(&thread, NULL, thr_fn, NULL)) { printf("error when create pthread,%d ", errno); return 1; } char c ; while ((c = getchar()) != 'q'); printf("Now terminate the thread! "); flag = 0; printf("Wait for thread to exit "); pthread_join(thread, NULL); printf("Bye "); 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：
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#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("***** "); 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 "); } 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 ", errno); return 1; } char c ; while ((c = getchar()) != 'q'); printf("Now terminate the thread! "); pthread_mutex_lock(&mutex); flag = 0; pthread_cond_signal(&cond); pthread_mutex_unlock(&mutex); printf("Wait for thread to exit "); pthread_join(thread, NULL); printf("Bye "); 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）。