Can we force quit a C program's execution after a fraction of seconds

Question

Can we force quit a C program's execution after a fraction of seconds (range of milliseconds) or by the size of memory it uses? This way, I want to restrict printing content in an infinite loop and restrict buffer overruns.

I am using cygwin GCC4.3 compiler and want to implement it as a tool in PHP, which takes in the C source as input and displays the corresponding output.

PS - 1. I say milliseconds because my C problems will only involve very simple arithmetic/computations. 2. To restrict the execution time, set_time_limit()in php would restrict the entire PHP script's execution time and not the time allotted to exec( )

Answer 1

You should be able to use the alarm() function. While it is found in unistd.h it is a POSIX.1-2001 function and should be available under cygwin. If SIGALRM is not handled it kills the process.

Try it:

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

int main() {

     alarm(5); /* raise alarm after 5 seconds */
     
     while(1) {
             printf("Running forever\n");
     }
     return 0; /* never reached */
}

update

As jonathan points out alarm(2) only works in seconds so you can use setitimer instead (also POSIX compliant)

#include <stdio.h>
#include <sys/time.h>

int main() {

     /* --CUT HERE-- */
     struct itimerval timer;
     timer.it_value.tv_sec = 0;
     timer.it_value.tv_usec = 5000; /* 5 milliseconds */
     timer.it_interval.tv_sec = 0;
     timer.it_interval.tv_usec = 0; 

     setitimer(ITIMER_REAL, &timer, NULL);
     /* --END CUT-- */
     while(1) {
             printf("Running forever\n");
     }
     return 0; /* never reached */
}

if the above works on your system, copy code from --CUT HERE-- to --END CUT-- and paste it into your main;

update 2

to limit memory try using setrlimit:

see Set stack size with setrlimit() and provoke a stack overflow/segfault

for an example