shashankagrawal's blog

How to change default stack size in linux?
By shashankagrawal, history, 4 years ago, In English

We can change stack size in linux temporarily by using the command ulimit -s new_value, But is there any way to change stack size permanently, or Can we do something within C++ code, so it will change stack size by itself?

I tried changing this, but It didn't work. I faced this issue in hackercup qualification round D2, terminal gave segfault, and later I came to know about the low value of default stack size in linux.

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4 years ago, # |
  Vote: I like it +21 Vote: I do not like it

After altering limits.conf, have you tried logging off and logging back into your account? I believe the changes won't come into effect unless you do this.

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    4 years ago, # ^ |
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    Yes, I did it, But It didn't work somehow

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    4 years ago, # ^ |
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    I added this-> @my_username soft stack 2000000 in limits.conf, Is there any mistake in this line?

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      4 years ago, # ^ |
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      I think you should not put @ before your username.

      I added this my_username soft stack 262144 and it worked well.

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4 years ago, # |
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I feel u bro, same thing happened to me, but even worse I was on Windows using VS code, spent half an hour trying to find what's the problem :( then after a long search edited my compilation flags as shown here

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    4 years ago, # ^ |
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    Yeah, sad!

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    4 years ago, # ^ |
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    Given link work only for codeblocks. Is there any way/command-flag which i can use in VScode for this purpose?

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      4 years ago, # ^ |
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      I don't use codeblocks, just edited my compilation flags, whatever IDE u might be using, search in your setting how to edit your compilation flags and it should work fine

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4 years ago, # |
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Just typing ulimit -s into terminal should give you the default stack size. For me, it's 8192, i.e. 8 MiB.

To change the stack size in the code, you can use getrlimit() and setrlimit() system calls:

#include <sys/resource.h>

int main() {
    rlimit rlim;
    if (getrlimit(RLIMIT_STACK, &rlim)) return 1;
    rlim.rlim_cur = rlim.rlim_max;
    // You can set the fixed value instead of max value, e.g. rlim.rlim_cur = 1024 * 1024 * 1024
    // will set your stack size to 1 GiB
    if (setrlimit(RLIMIT_STACK, &rlim)) return 2;

    // Your code here...

    return 0;
}

Note that this example will work only for UNIX-like systems, so it's better to disable this code (using #ifdef, for example) when submitting to an online judge.

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    4 years ago, # ^ |
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    Thank you very much!

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    4 years ago, # ^ |
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    Is it a good idea to have stack size something as big as 1 gb when default size is like 8MB?

    Does it have any side-effects?

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      4 years ago, # ^ |
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      If you have infinite recursion, then your program crashes much later, and possibly after consuming all system memory.

      Suggestion: Leave it as default and raise only when needed in individual cases.

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        4 years ago, # ^ |
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        Does the same occur on increasing it not to rlim_max but to 1 Gb instead ?

        P.S — just curious because i added it in my snippet and made limit to 1 Gb and it should return segmentation fault after crossing the 1 Gb limit but I'm not in mood to try after reading your Comment.

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          4 years ago, # ^ |
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          If you increase it to 1 GiB, then the program will segfault if it tries to exceed this limit. If you always have 1 GiB of free memory while solving contests, everything should be fine.

          Also I noticed that I made a tiny mistake in the comment above, which is fixed now. setrlimit() takes stack size in bytes, so 1 GiB would be rlim.rlim_cur = 1024 * 1024 * 1024. If you added this code into your snippet, it's better to fix it.

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        4 years ago, # ^ |
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        I use the following wrapper to run the solutions locally:

        bash -c 'ulimit -s 262144 && ulimit -v 2097152 && time "./%e"'

        ulimit -v is used to limit the amount of memory, so I won't go out of memory in case of infinite memory allocation.

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4 years ago, # |
  Vote: I like it +29 Vote: I do not like it

I failed D2 because of the exact same issue :(

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3 years ago, # |
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Maybe you can just add ulimit -s new_value to your .bashrc file?

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