Would this be considered a memory leak?

Question

Consider this pointless program:

/* main.c */

#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv) {
    int i;
    for (i = 0; i < 1024; i++) {
        int pid = fork();
        int status;
        if (pid) {
            wait(&status);
        }
        else {
            char *ptr = (char *)malloc(1024*sizeof(char));
            char *args[2] = {"Hello, world!", NULL};
            execve("/bin/echo", args, NULL);
        }
    }
}

Would not freeing ptr constitute a memory leak for either main.c or the other program, or is it going to be freed anyway when execve is called?

I'd sleep better with `free(ptr);` before the execve – pmg Sep 20 '10 at 23:06 — pmg, Sep 20 '10 at 23:06

Drew Hall · Accepted Answer · 2010-09-20T23:33:58.503

10

No.

This is not a memory leak. exec*() will make a local copy of the string data in the args array, then blow away the child process memory image and overlay it with the memory image used by /bin/echo. Essentially all that remains after the exec() is the pid.

Edit:

User318904 brought up the case of exec() returning -1 (i.e., failure). In this case, the child process that has forked but failed to exec does, indeed technically have a memory leak, but as the usual response to a failed exec is to just exit the child process anyways, the memory will be reclaimed by the OS. Still, freeing it is probably a good habit to get into, if for no other reason than that it will keep you from wondering about it later on.

edited Sep 20 '10 at 23:33

answered Sep 20 '10 at 23:00

Drew Hall

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Thanks. It's not an issue of my being too lazy to add free(ptr). In the actual, slightly-more-complicated case that I have in my real program, I'm actually passing a malloc'ed string to execve, so I'm unable to free it (though I do call free if execve fails). – Nick Sep 21 '10 at 00:06
@Nick: The source of the memory (stack, heap, static) is irrelevant to the OS--it's all just memory, and it will be replaced and reclaimed automatically and painlessly by the OS. – Drew Hall Sep 21 '10 at 01:08

score 3 · Answer 2 · answered Sep 20 '10 at 23:04

3

When execve returns -1, yes. Otherwise, maybe.

answered Sep 20 '10 at 23:04

user318904

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che · Answer 3 · 2011-05-29T16:07:30.073

0

The allocated memory should be freed by exec. After the call completes you can't access it anyway.

edited May 29 '11 at 16:07

answered Sep 20 '10 at 23:00

che

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Would this be considered a memory leak?

3 Answers3