limits.c

BeginningLinuxProgramming example4

//  1  Make the includes for all the functions we're going to be using in this program.

#include <sys/types.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdio.h>

// 2  The void function writes a string to a temporary file 10000 times and then performs some arithmetic
// to generate load on the CPU.

void work()
{
    FILE *f;
    int i;
    double x = 4.5;

    f = tmpfile();
    for(i = 0; i < 10000; i++) {
        fprintf(f,"Do some output\n");
        if(ferror(f)) {
            fprintf(stderr,"Error writing to temporary file\n");
            exit(1);
        }
    }
    for(i = 0; i < 1000000; i++)
        x = log(x*x + 3.21);
}

//  3  The main function calls work and then uses the getrusage function to discover how much CPU time it has used. It displays this information on screen.

int main()
{
    struct rusage r_usage;
    struct rlimit r_limit;
    int priority;

    work();
    getrusage(RUSAGE_SELF, &r_usage);

    printf("CPU usage: User = %ld.%06ld, System = %ld.%06ld\n",
        r_usage.ru_utime.tv_sec, r_usage.ru_utime.tv_usec,
        r_usage.ru_stime.tv_sec, r_usage.ru_stime.tv_usec);

//  4  Next, it calls getpriority and getrlimit to find out its current priority and file size limits respectively.

    priority = getpriority(PRIO_PROCESS, getpid());
    printf("Current priority = %d\n", priority);

    getrlimit(RLIMIT_FSIZE, &r_limit);
    printf("Current FSIZE limit: soft = %ld, hard = %ld\n",
        r_limit.rlim_cur, r_limit.rlim_max);

//  5  Finally, we set a file size limit using setrlimit and call work again, which fails because 
//  it attempts to create too large a file.

    r_limit.rlim_cur = 2048;
    r_limit.rlim_max = 4096;
    printf("Setting a 2K file size limit\n");
    setrlimit(RLIMIT_FSIZE, &r_limit);

    work();
    exit(0);
}