C program causes memory leak?

Question

I use that very simple C program to execute a system call to php each second, in order to run a php script that sends pending push notification in my database to APNS (Apple notification service).

Anyway, this program causes a memory overflow after about 10 hours, so I reduced sleep time between thread creation from 1s to 10000us, and I could see in real time with htop that memory were increasing without never lower. Here is the program :

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

typedef struct {
    char* script_path ;
} arg_for_script ;

static void *start_instance(void *_args)
{
    int id = abs(pthread_self());
    arg_for_script* args = _args ;

    printf("[SERVICE] start php script on thread %d\n",id);
    fflush(stdout);
    char cmd[200] ;

    sprintf(cmd, "php -f %s %d", args->script_path, id );

    system(cmd);

    printf("[SERVICE] end of script on thread %d\n", id);
    fflush(stdout);



    pthread_exit(NULL);
}

int main(int argc, char* argv[])
{


    if(argc < 2)
    {
        fprintf(stderr, "[SERVICE] Path of php notification script must be filled\n");
        fflush(stderr);
        return EXIT_FAILURE;
    }

    arg_for_script args ;

    args.script_path = argv[1];

    pthread_attr_t tattr ;
    struct sched_param param;
    param.sched_priority = 1 ;

    pthread_attr_init(&tattr);

    pthread_attr_setinheritsched(&tattr, PTHREAD_EXPLICIT_SCHED);
    pthread_attr_setschedpolicy(&tattr, SCHED_FIFO);
    pthread_attr_setschedparam(&tattr, &param);



    while(1) {
        pthread_t thrd;

      //  if(pthread_create(&thrd, &tattr, start_instance, (void *)&args) == -1) {
        if(pthread_create(&thrd, NULL, start_instance, (void *)&args) == -1)
        {
            fprintf(stderr, "[SERVICE] Unable to create thread\n");
            fflush(stderr);
            return EXIT_FAILURE;
        }

        usleep( 10000);
    }

  //  pthread_attr_destroy(&tattr);
    return EXIT_SUCCESS ;

}

Here, I don't dynamically allocate any RAM with malloc. Why would this program increases memory usage ? What pointer should I free here ?

Answer 1

You aren't calling pthread_join() nor use pthread_detach(), so the resources allocated for the thread aren't freed. Namely each thread has it's own stack, which is probably what causes the rising memory consumption.

Some remarks about your implementation: Since you plan on executing a PHP script with system() and don't actually need to work on shared variables or file descriptors, it's better to use fork() and one of the variants of exec(). This will spawn a new process without the intermediate step of creating a thread. It's also not recommended to use system() because it often allows to exploit the program when the input isn't properly sanitized. In this case it might be fine, if you only call it manually.