Linux多線程編程 - 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; }
輸入q後，需要等線程從sleep中醒來（由掛起狀態變為運行狀態），即最壞情況要等10s，線程才會被join。采用sleep的缺點：不能及時喚醒線程。
采用pthread_cond_timedwait函數，條件到了，線程即會被join，可及時喚醒線程。實現的如下：
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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("*****\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()函數阻塞住調用該函數的線程，等待由cond指定的條件被觸發（pthread_cond_broadcast() or pthread_cond_signal()）。
當pthread_cond_timedwait()被調用時，調用線程必須已經鎖住了mutex。函數pthread_cond_timedwait()會對mutex進行【解鎖和執行對條件的等待】（原子操作）。
Linux多線程編程 - sleep 和 pthread_cond_timedwait