threaded programs report bogus process size ?

[Nicolas Joly <njoly%pasteur.fr@localhost>]

Hi,

I just noticed that threaded processes may report increasing process
size of their life ...

The following sample which create a single thread in a loop does
illustrate this strange behaviour.

njoly@lanfeust [~]> cat thr_loop.c 
#include <err.h>
#include <pthread.h>

void *thr_func(void *arg) { return NULL; }

int main() {
  int res;
  pthread_t thr;

  while (1) {
    res = pthread_create(&thr, NULL, thr_func, NULL);
    if (res != 0)
      errx(1, "pthread_create failed");
    res = pthread_join(thr, NULL);
    if (res != 0)
      errx(1, "pthread_join failed");
  }
  return 0; }
njoly@lanfeust [~]> cc -pthread -o thr_loop thr_loop.c 
njoly@lanfeust [~]> ./thr_loop 

And then, both top(1) and ps(1) report an increasing process size over
the time.

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
11242 njoly     36    0    57M 1224K RUN/1      0:02  8.51%  4.49% thr_loop
[...]
11242 njoly     39    0   119M 1596K RUN/0      0:04  0.00%  6.40% thr_loop
[...]
11242 njoly     39    0   161M 1848K RUN/0      0:06  0.00%  7.03% thr_loop
[...]
11242 njoly     37    0   203M 2100K CPU/1      0:08  0.00%  7.57% thr_loop

I'm not sure this is a critical problem, as i do not see any drawback
with such a 19GB process in my machine; but i'm wondering where does
such numbers come from.

Any hint ?

Thanks.

-- 
Nicolas Joly

Biological Software and Databanks.
Institut Pasteur, Paris.