原文地址:https://blog.csdn.net/dead_g/article/details/73338960
由於工作上的事情,要用到線程之間的同步,而且有超時處理,在網上看到了使用pthread_cond_timedwait()函數和pthread_cond_wait()函數,其實2個函數都差不多,我主要是要用pthread_cond_timedwait()函數。
pthread_cond_timedwait()函數有三個入口參數:
(1)pthread_cond_t __cond:條件變量(觸發條件)
(2)pthread_mutex_t __mutex: 互斥鎖
(3)struct timespec __abstime: 等待時間(其值爲系統時間 + 等待時間)
當在指定時間內有信號傳過來時,pthread_cond_timedwait()返回0,否則返回一個非0數(我沒有找到返回值的定義);
在使用pthread_cond_timedwait()函數時,必須有三步:
1:加互斥鎖:pthread_mutex_lock(&__mutex)
2:等待:pthread_cond_timedwait(&__cond, &__mutex, &__abstime) //解鎖->等待->加鎖
3:解互斥鎖:pthread_mutex_unlock(&__mutex)
發送信號量時,也要有三步:
1:加互斥鎖:pthread_mutex_lock(&__mutex)
2:發送:pthread_cond_signal(&__cond)
3:解互斥鎖:pthread_mutex_unlock(&__mutex)
那麼,這裏就有一個問題,等待的時候已經加上鎖了,那麼我發送的時候怎麼才能運行到發送函數呢?其實這是因爲在pthread_cond_timedwait()函數中已經對互斥鎖進行解鎖操作了,所以這個時候發送信號量是不會阻塞的。其實仔細想想,這樣不是才能保證同步嗎?(寫完代碼後考慮一下)
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>
#include <sys/time.h>
#define SENDSIGTIME 10
pthread_cond_t g_cond;
pthread_mutex_t g_mutex;
void thread1(void *arg)
{
int inArg = (int)arg;
int ret = 0;
struct timeval now;
struct timespec outtime;
pthread_mutex_lock(&g_mutex);
gettimeofday(&now, NULL);
outtime.tv_sec = now.tv_sec + 5;
outtime.tv_nsec = now.tv_usec * 1000;
ret = pthread_cond_timedwait(&g_cond, &g_mutex, &outtime);
//ret = pthread_cond_wait(&g_cond, &g_mutex);
pthread_mutex_unlock(&g_mutex);
printf("thread 1 ret: %d\n", ret);
}
int main(void)
{
pthread_t id1;
int ret;
pthread_cond_init(&g_cond, NULL);
pthread_mutex_init(&g_mutex, NULL);
ret = pthread_create(&id1, NULL, (void *)thread1, (void *)1);
if (0 != ret)
{
printf("thread 1 create failed!\n");
return 1;
}
printf("等待%ds發送信號!\n", SENDSIGTIME);
sleep(SENDSIGTIME);
printf("正在發送信號....\n");
pthread_mutex_lock(&g_mutex);
pthread_cond_signal(&g_cond);
pthread_mutex_unlock(&g_mutex);
pthread_join(id1, NULL);
pthread_cond_destroy(&g_cond);
pthread_mutex_destroy(&g_mutex);
return 0;
}
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作者:dead_g
來源:CSDN
原文:https://blog.csdn.net/dead_g/article/details/73338960
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