上一篇文章，讲到了如何用getrlimit获取进程资源上限。既然能getrlimit，那当然我们也可以setrlimit，对进程的资源进行限制。我们就以进程的CPU时间和占用的内存为例，讲述如何限制进程相应的资源以及当资源上限超过时，是如何捕捉的。

一个对子进程的资源（时间和内存）进行限制的程序：

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>

#define SYSTEM_ERROR        10

#define MIN_TIME_LIMIT 1
#define MAX_TIME_LIMIT 100
#define MIN_MEM_LIMIT 4
#define MAX_MEM_LIMIT 1024

struct rlimit tLimit, mLimit;

int main (int argc, char** argv)
{
    int timeLimit, memLimit, ret;
    pid_t pid;
    int s;
    struct rusage rUsage;
    double passTime;
    char** childCmd;

    if ( argc < 4 )
    {
        printf("argument number error!\n");
        printf("usage: timeLimt(%d~%ds) memoryLimit(%d~%dMb) commandLine\n",
                MIN_TIME_LIMIT, MAX_TIME_LIMIT, MIN_MEM_LIMIT, MAX_MEM_LIMIT);
        return SYSTEM_ERROR;
    }
    //获取时间限制和内存限制
    if ( isdigit(argv[1][0]) )
        timeLimit = atoi(argv[1]);
    if ( isdigit(argv[2][0]) )
        memLimit = atoi(argv[2]);
    if ( timeLimit < MIN_TIME_LIMIT || timeLimit > MAX_TIME_LIMIT )
    {
        printf("time limit argument error!(%d~%ds)\n", MIN_TIME_LIMIT, MAX_TIME_LIMIT);
        return SYSTEM_ERROR;
    }
    if ( memLimit < MIN_MEM_LIMIT || memLimit > MAX_MEM_LIMIT )
    {
        printf("memory limit argument error!(%d~%dMb)\n", MIN_MEM_LIMIT, MAX_MEM_LIMIT);
        return SYSTEM_ERROR;
    }
    memLimit = memLimit * 1024 * 1024;

    if ( (pid=fork()) < 0 )
    {
        printf("fork error!\n");
        return SYSTEM_ERROR;
    }
    else if ( pid == 0 )        /*child process*/
    {
        getrlimit(RLIMIT_CPU, &tLimit);
        getrlimit(RLIMIT_AS, &mLimit);

        tLimit.rlim_cur = timeLimit;
        mLimit.rlim_cur = memLimit;

        if ( setrlimit(RLIMIT_CPU, &tLimit) == -1 )     /*设置时间限制*/
            printf("setrlimit time limit error!\n");
        if ( setrlimit(RLIMIT_AS, &mLimit) == -1 )      /*设置内存限制*/
            printf("setrlimit memory limit error!\n");

        childCmd = argv + 3;
        execvp(childCmd[0], childCmd);
    }
    else
    {
        waitpid(pid, &s, 0);        //等待子进程结束，并获取信号
        printf("================parent process=====================\n");
        printf("child exit status: %d\n", s);
        if ( WIFEXITED(s) )
            printf("exit normally.\n");
        else
            printf("exit abnormally.\n");
        if ( WIFSIGNALED(s) )
            printf("exit by signal: %d | %d\n", s, WTERMSIG(s));
        printf("parent process is finished.\n");
        getrusage(RUSAGE_CHILDREN, &rUsage);
        passTime = (rUsage.ru_utime.tv_sec + rUsage.ru_stime.tv_sec) * 1000 + (float)(rUsage.ru_stime.tv_usec + rUsage.ru_utime.tv_usec) / 1000;
        printf("child process time: %d ms\n", (int)passTime);
        printf("===================================================\n\n");
        return 0;
    }
}

好了，下面我们写几个测试程序。

第一个，写个占用CPU时间很长的程序：

#include <stdio.h>
#include <unistd.h>

const int MAX = 50000;

int main ()
{
    int i, j, k;
    for (i = 0; i < MAX; i ++)
        for (j = 0; j < MAX; j ++)
            k = i * j;
    return 0;
}

测试运行结果：

> quxiao@quxiao-laptop:~/learnLinux/setrlimit$ ./setrlimit_ex.o 1 64 ./run_so_long.o

================parent process=====================

child exit status: 24

exit abnormally.

exit by signal: 24 | 24

parent process is finished.

child process time: 1000 ms

===================================================

信号24是SIGXCPU信号，表示超出CPU时间上限（我们的程序中为1s）。

好，再写个申请过多内存空间的程序：

#define MAX 10000

int arr[MAX][MAX];

int main ()
{
    return 0;
}

测试运行结果：

> quxiao@quxiao-laptop:~/learnLinux/setrlimit$ ./setrlimit_ex.o 1 64 ./so_long_array.o

================parent process=====================

child exit status: 9

exit abnormally.

exit by signal: 9 | 9

parent process is finished.

child process time: 0 ms

===================================================

信号9表示SIGKILL，申请过多内存空间时会产生该信号。（还有哪些情况会产生这个信号？）

这样，我们就可以对进程的行为进行限制，并测量进程的各项资源了。（这也是我们的OJ所需要的 :) ）

具体所有信号所表示的含义，可以查看这里。