带超时的system

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我是靠谱客的博主勤恳猫咪，最近开发中收集的这篇文章主要介绍带超时的system，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

工作中，需要使用tftp等协议下载一些文件，但这时候遇到一个问题就是当tftp的服务器没有打开时，system

函数会阻塞较长时间(长达树秒),这时候首先想到的就是设置tftp的超时参数，但因为还有很多协议也有超时返回

的需求，我就想一劳永逸的封装一个函数来完成这项任务。最后决定重写一下system并设置超时函数，封装的函数

如下(system_timeout).这里需要解释进行两层封装的原因:在system_timeout中我们将_system_timeout进行了一层封装，

并将信号SIGCHLD设置为SIG_DFL是因为我们在_system_timeout中调用了waitpid,而这个函数在SIGCHLD被忽略是会

产生ECHILD错误，手册解释如下:

ERRORS

ECHILD (for waitpid() or waitid()) The process specified by pid (wait-pid()) or idtype and id (waitid()) does

not exist or is not a child of the calling process. (This can happen for one's own child if the action for SIGCHLD

is set to SIG_IGN. See also the Linux Notes section about threads.)

#include <sys/wait.h>
#include <errno.h>
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int _system_timeout(const char *cmdstring, int timeout);    /*one hundred of a second*/
int system_timeout(const char *cmdstring, int timeout);  

int main(int argc, char **argv)
{
    if (argc != 2) {
        printf("usage:%s [command]n", argv[0]);
    }
    if (0 != system_timeout(argv[1], 50)) {
        printf("system_timeout error n");
        return -1;
    }
    printf("system_timeout successn");
    return 0;
}

int _system_timeout(const char *cmdstring, int timeout)
{
    pid_t pid;
    int status;
    struct sigaction ignore, saveintr, savequit;
    sigset_t chldmask, savemask;

    if (cmdstring == NULL)
        return 1;
    ignore.sa_handler = SIG_IGN;
    sigemptyset(&ignore.sa_mask);
    ignore.sa_flags = 0;
    if (sigaction(SIGINT, &ignore, &saveintr) < 0) {
        return -1;
    }
    if (sigaction(SIGQUIT, &ignore, &savequit) < 0) {
        return -1;
    }
    sigemptyset(&chldmask);
    sigaddset(&chldmask, SIGCHLD);
    if (sigprocmask(SIG_BLOCK, &chldmask, &savemask) < 0) {
        return -1;
    }
    if ((pid = fork()) < 0) {
        return -1;
    } else if (pid == 0) {
        sigaction(SIGINT, &saveintr, NULL);
        sigaction(SIGQUIT, &savequit, NULL);
        sigprocmask(SIG_SETMASK, &savemask, NULL);
        execl("/bin/sh", "sh", "-c", cmdstring, (char *)0);
        _exit(127);
    } else {
        usleep(timeout * 10000);
        kill(pid, SIGKILL);
        waitpid(pid, &status, 0);
    }
    if (sigaction(SIGINT, &saveintr, NULL) < 0) {
        return -1;
    }
    if (sigaction(SIGQUIT, &savequit, NULL) < 0) 
        return -1;
    if (sigprocmask(SIG_SETMASK, &savemask, NULL) < 0)
        return -1;
    return status;
}

int system_timeout(const char *cmdstring, int timeout)
{
    int ret = 0;
    struct sigaction chldnew, chldold;
    if (cmdstring == NULL) 
        return -1;
    bzero(&chldnew, sizeof(struct sigaction));
    bzero(&chldold, sizeof(struct sigaction));
    chldnew.sa_handler = SIG_DFL;
    sigemptyset(&chldnew.sa_mask);
    chldnew.sa_flags = 0;
    if (sigaction(SIGCHLD, &chldnew, &chldold) < 0) {
        return -1;
    }
    if ((timeout * 10000) < 0) {
        return -1;
    } else if (timeout == 0) {
        ret = system(cmdstring);
    } else {
        ret = _system_timeout(cmdstring, timeout);
    }
    if (sigaction(SIGCHLD, &chldold, NULL) < 0) {
        return -1;
    }
    return ret;
}

转自:https://blog.csdn.net/shanguangy111/article/details/47185533

这块需要视项目的实际情况来修改代码即可。