如何在C中设置函数的超时？

Question

我要求我必须给xx ms执行一个函数.在xx ms之后我必须中止该功能.请帮我解决如何在C中实现它.

Answer 1

我认为最好的方法是使用pthreads.启动可能需要在其自己的线程中取消的计算,并在主线程中使用pthread_cond_timedwait:

#include <time.h>
#include <pthread.h>
#include <stdio.h>
/* for ETIMEDOUT */
#include <errno.h>
#include <string.h>

pthread_mutex_t calculating = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t done = PTHREAD_COND_INITIALIZER;

void *expensive_call(void *data)
{
        int oldtype;

        /* allow the thread to be killed at any time */
        pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &oldtype);

        /* ... calculations and expensive io here, for example:
         * infinitely loop
         */
        for (;;) {}

        /* wake up the caller if we've completed in time */
        pthread_cond_signal(&done);
        return NULL;
}

/* note: this is not thread safe as it uses a global condition/mutex */
int do_or_timeout(struct timespec *max_wait)
{
        struct timespec abs_time;
        pthread_t tid;
        int err;

        pthread_mutex_lock(&calculating);

        /* pthread cond_timedwait expects an absolute time to wait until */
        clock_gettime(CLOCK_REALTIME, &abs_time);
        abs_time.tv_sec += max_wait->tv_sec;
        abs_time.tv_nsec += max_wait->tv_nsec;

        pthread_create(&tid, NULL, expensive_call, NULL);

        /* pthread_cond_timedwait can return spuriously: this should
         * be in a loop for production code
         */
        err = pthread_cond_timedwait(&done, &calculating, &abs_time);

        if (err == ETIMEDOUT)
                fprintf(stderr, "%s: calculation timed out\n", __func__);

        if (!err)
                pthread_mutex_unlock(&calculating);

        return err;
}

int main()
{
        struct timespec max_wait;

        memset(&max_wait, 0, sizeof(max_wait));

        /* wait at most 2 seconds */
        max_wait.tv_sec = 2;
        do_or_timeout(&max_wait);

        return 0;
}

你可以在linux上编译并运行它:

$ gcc test.c -pthread -lrt && ./a.out
do_or_timeout: calculation timed out

Answer 2

->include time.h 
->take two variable for start time & current time of type time_t
like time_t start_time,current_time
-> take start time 
   time(&start_time);
now in while loop continuisly check for 
   time(&current_time)
   difftime(current_time,start_time)
if difftime's return value is 15ms break while loop & close your program