How to set timeout for gcc compilation of .c file on linux - c

Question

I am trying to compile a C code through my php script using gcc on a linux machine. But if the C code contains an infinite loop , the compiler gets stucked.
my PHP script goes like this ..
shell_exec('gcc input.c -o output 2> compile.txt');
$output=shell_exec('./output');
The 'input.c' file goes like this..
#include<stdio.h.
void main()
{
while(1)
prinf("This is infinite loop");
}
When I compile the PHP code , it gives an
**PHP Fatal error: Out of memory (allocated 403177472) (tried to allocate 804896768 bytes)**
I've tried timeout 5s :
$output=shell_exec('./output');
but it doesn't work although it works if i do ..
int i;
while(1)
{
scanf("%d",&i);
}
..in my input.c file. I have seached a lot but in vain..
What am I doing wrong.?

Answer 1

The first point is that, it is not the compiler which is getting stuck. The compiler compiles code fine. It is during execution that your code is going into a infinite loop. So, incase of your first code, it just keeps executing without any pause or exit and hogs the CPU all the time which gives a feeling of "being stuck".
With regard to how your second code works, it is because you are pausing for getting an input. But, again, in that case, you have failed provide an exit for your program. So, effectively, the second code is same as your first code, but it just doesn't hog the CPU.
There is only one way for you to correct this problem, that is by modifying your 'C' code not to have an infinite loop without any exit.
Example:
int i;
while(1)
{
scanf("%d",&i);
if(0 == i)
{
break; //Just an example as to how you can exit from an infinite loop
}
}

Answer 2

You can use ulimit in the invocation of the program. E.g. the following will limit output to 1 second of CPU time:
shell_exec("ulimit -t 1; ./output")
It might be a good idea to limit other resources too, so that output can't use all your memory etc.
(Note that this limits CPU time, not absolute time. If you want to do that, you should look at a program like timelimit, which would be called like shell_exec("timelimit -T 1 ./output"), I think.)

Answer 3

Jay explains much of it very well. The rest of it is that your first program not only goes into an infinite loop, but also produces an infinite amount of output, all of which you try to store in $output. I'd say you're lucky you didn't crash your computer, but PHP probably saved you with a built-in memory limit.

Answer 4

What you are looking for is possible theoretically:
You can read about the halting problem
However, you can probably use something like PHP's set_time_limit