Re: Problem with stack size in pthreads

[Andreas Jaeger <aj at suse dot de>]

Ulrich Drepper <drepper@redhat.com> writes:

> Andreas Jaeger <aj@suse.de> writes:
> 
>> If the stack pointer of the initial thread in function thread_self
>> (from internals.h) is below __pthread_initial_thread_bos, it's not
>> considered in the initial thread.
> 
> This is not supposed to happen because we made a setrlimit() call.
> Testcase?

Here's one.  It creates first some data on the stack before calling
the first thread.

With the LDT implementation on i686, I get:
$ ./jdk-thread
rlim.rlim_cur = RLIM_INFINITY
Thread 400: allocated key 1
Thread 400: allocating buffer at 0x8049da8
starting Process second
Thread 803: allocating buffer at 0x804c198
Thread 803: "Result of second thread"
Thread 803: freeing buffer at 0x804c198
starting Process first
Thread 402: allocating buffer at 0x804c198
Thread 402: "Result of first thread"
Thread 402: freeing buffer at 0x804c198
Thread 400: "Result of initial thread"

And without, on i686:
gee:~/tmp:[0]$ ./jdk-thread
rlim.rlim_cur = RLIM_INFINITY
Segmentation fault

or on powerpc:
cantaloupe:~/tmp:[139]$ gcc -Wall jdk-thread.c -O2 -lpthread -o jdk-thread -g
cantaloupe:~/tmp:[0]$ ./jdk-thread
rlim.rlim_cur = RLIM_INFINITY
Segmentation fault
cantaloupe:~/tmp:[139]$ 

Andreas

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>


pthread_key_t key;


/* This is a typical example of a library function that uses
   static variables to accumulate results between calls.
   Here, it just returns the concatenation of all string arguments
   that were given to it. */

/* Of course, this cannot be used in a multi-threaded program
   because all threads store "accu" at the same location.
   So, we'll use thread-specific data to have a different "accu"
   for each thread. */

/* Key identifying the thread-specific data */
static pthread_key_t str_key;
/* "Once" variable ensuring that the key for str_alloc will be allocated
   exactly once. */
static pthread_once_t str_alloc_key_once = PTHREAD_ONCE_INIT;

/* Forward functions */
static void str_alloc_key (void);
static void str_alloc_destroy_accu (void *accu);

/* Thread-safe version of str_accumulate */

static char *
str_accumulate (const char *s)
{
  char *accu;

  /* Make sure the key is allocated */
  pthread_once (&str_alloc_key_once, str_alloc_key);
  /* Get the thread-specific data associated with the key */
  accu = (char *) pthread_getspecific (str_key);
  /* It's initially NULL, meaning that we must allocate the buffer first. */
  if (accu == NULL)
    {
      accu = malloc (1024);
      if (accu == NULL)
	return NULL;
      accu[0] = 0;
      /* Store the buffer pointer in the thread-specific data. */
      pthread_setspecific (str_key, (void *) accu);
      printf ("Thread %lx: allocating buffer at %p\n", pthread_self (), accu);
    }
  /* Now we can use accu just as in the non thread-safe code. */
  strcat (accu, s);
  return accu;
}

/* Function to allocate the key for str_alloc thread-specific data. */

static void
str_alloc_key (void)
{
  pthread_key_create (&str_key, str_alloc_destroy_accu);
  printf ("Thread %lx: allocated key %d\n", pthread_self (), str_key);
}

/* Function to free the buffer when the thread exits. */
/* Called only when the thread-specific data is not NULL. */

static void
str_alloc_destroy_accu (void *accu)
{
  printf ("Thread %lx: freeing buffer at %p\n", pthread_self (), accu);
  free (accu);
}

/* Test program */

static void *
process (void *arg)
{
  char *res;
  printf ("starting Process %s\n", (char*) arg);
  
  res = str_accumulate ("Result of ");
  res = str_accumulate ((char *) arg);
  res = str_accumulate (" thread");
  printf ("Thread %lx: \"%s\"\n", pthread_self (), res);
  return NULL;
}

static void
start_threading (void)
{
  char *res;
  pthread_t th1, th2;

  res = str_accumulate ("Result of ");
  pthread_create (&th1, NULL, process, (void *) "first");
  pthread_create (&th2, NULL, process, (void *) "second");
  res = str_accumulate ("initial thread");
  printf ("Thread %lx: \"%s\"\n", pthread_self (), res);
  pthread_join (th1, NULL);
  pthread_join (th2, NULL);
}


void
enlarge_stack (int i)
{
  if (i > 8192)
    start_threading ();
  else
    {
      char c[1024];

      c [i %1024] = '\0';
      enlarge_stack (i+1);
    }
}



int
main (void)
{
  struct rlimit rlim;

  getrlimit(RLIMIT_STACK, &rlim);
  if (rlim.rlim_cur == RLIM_INFINITY)
    printf ("rlim.rlim_cur = RLIM_INFINITY\n");
  else
    printf("rlim_cur = %ldk, rlim_max = %ldk\n", rlim.rlim_cur/1024, rlim.rlim_max/1024);
  
  pthread_key_create(&key, NULL);
  pthread_setspecific(key, (void *)95);

  enlarge_stack (0);

  return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj