[英]pthread_cond_timedwait returns ETIMEDOUT immediately
I am trying to use pthread_cond_timedwait
to wait with a timeout similar to Java's wait(long timeout, int nanos)
. 我正在尝试使用pthread_cond_timedwait
来等待类似于Java的wait(long timeout, int nanos)
。 I understand that Java's wait
uses a relative timeout, whereas pthread_cond_timedwait
uses an absolute time threshold. 我知道Java的wait
使用相对超时,而pthread_cond_timedwait
使用绝对时间阈值。 Despite taking this into account, pthread_cond_timedwait
appears to return immediately with the error code ETIMEDOUT. 尽管考虑到这一点, pthread_cond_timedwait
似乎立即返回,并显示错误代码ETIMEDOUT。
The sample program below prints a value <0. 下面的示例程序打印一个值<0。 I would expect it to print a value >=0. 我希望它可以打印> = 0的值。
Am I using pthread_cond_timedwait
incorrectly? 我使用pthread_cond_timedwait
不正确吗? How would I rewrite the below program to add a delay of eg 5 seconds? 我如何重写下面的程序以增加例如5秒的延迟?
#define _POSIX_C_SOURCE 199309L
#include <stdio.h>
#include <pthread.h>
#include <time.h>
#include <errno.h>
int main(void) {
pthread_mutex_t mutex;
pthread_cond_t cond;
pthread_mutex_init(&mutex, NULL);
pthread_cond_init(&cond, NULL);
pthread_mutex_lock(&mutex);
struct timespec t1;
struct timespec t2;
clock_gettime(CLOCK_MONOTONIC, &t1);
t1.tv_sec += 5;
while(pthread_cond_timedwait(&cond, &mutex, &t1) != ETIMEDOUT);
clock_gettime(CLOCK_MONOTONIC, &t2);
printf("%d", t2.tv_sec - t1.tv_sec);
pthread_mutex_unlock(&mutex);
pthread_mutex_destroy(&mutex);
pthread_cond_destroy(&cond);
return 0;
}
You are using the wrong clock. 您使用了错误的时钟。 The default clock used by pthread_cond_timedwait
is CLOCK_REALTIME
. pthread_cond_timedwait
使用的默认时钟为CLOCK_REALTIME
。 If you really want to use CLOCK_MONOTONIC
instead, you'll need to set the clock attribute of your condition variable: 如果您确实想使用CLOCK_MONOTONIC
,则需要设置条件变量的clock属性:
pthread_condattr_t condattr;
pthread_condattr_init(&condattr);
pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC);
pthread_cond_init(&cond, &condattr);
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