Re: [bug #34140] gc not run correctly when allocating threads

[Andy Wingo]

Hi,

On Fri 26 Aug 2011 10:49, Stefan Israelsson Tampe <address@hidden> writes:

> On my machine this crashes after about 4000 iterations due to the oom killer.
> The reason is mainly that stack space is not reclaimed.
>
> (define (f n)
>   (let ((t (call-with-new-thread (lambda () 'ok))))
>     (join-thread t))
>   (if (= (modulo n 30) 0) 
>      (begin
>         (pk n) 
>         (pk (gc-stats)) 
>         (sleep 1)))
>   (f (+ n 1)))
>
>   (f 0)

Why is this, I wonder?  (Also, how much memory do you have, and what is
your architecture?  On my system each thread will allocate 512 KB by
default for a stack; if these thread stacks are not being collected,
4000 of them is 2 GB, which could hit the OOM on many systems.)

Anyway I could not reproduce it with the attached C program.  But the C
program isn't quite like what we do with threads, either; I suppose we
could try approximating the C program to the Scheme program.  We should
not have to introduce calls to `gc'; if the collector isn't collecting,
that's a problem!

Andy

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>

#define GC_THREADS 1
#define GC_REDIRECT_TO_LOCAL 1
#define GC_NO_THREAD_REDIRECTS 1

#include <gc/gc.h>

#define ALLOC_SIZE (64 * 1024 * sizeof(void*))

static void
fail (char *reason)
{
  perror (reason);
  exit (1);
}

static void*
thr_func (void* arg)
{
  void *mem = GC_malloc (ALLOC_SIZE);
  if (!mem)
    fail ("malloc failed");

  memset (mem, 1, ALLOC_SIZE);

  return NULL;
}

int main (int argc, char *argv[])
{
  GC_INIT ();
  
  int i, err, limit;
  void *res = NULL;

  limit = (argc == 2 ? atoi (argv[1]) : 10000);
  
  for (i = 0; i < limit; i++)
    {
      pthread_t thr;

      printf ("Spawning %d\n", i);

      if ((err = GC_pthread_create (&thr, NULL, thr_func, NULL)))
        fail ("pthread_create");

      if ((err = GC_pthread_join (thr, &res)))
        fail ("pthread_join");
    }

  printf ("Success.\n");  

  return 0;
}

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