[tbox-l] gdb useless for multithreaded (pthread) application

[Gabriel H. P. <pga...@rd...>]

Hi!

I have a problem with gdb crashing on AIX 5.2/32, 5.3/64 when trying to
debug 32 bit multithreaded applications.

The MT program works/runs fine as far as i can tell but i can not debug
it with either gdb 6.0 shipped in the aixtoolbox or with gdb 6.5 shipped
with PSDLIB.

Here is the test program I used:
========================  ptt.c ======================================
#include <pthread.h>
#include <stdio.h>

#define NUM_THREADS  3
#define TCOUNT 10
#define COUNT_LIMIT 12

int count = 0;
int thread_ids[3] = { 0, 1, 2 };
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *
inc_count (void *idp)
{
   int j, i;
   double result = 0.0;
   int *my_id = idp;

   for (i = 0; i < TCOUNT; i++)
   {
      pthread_mutex_lock (&count_mutex);
      count++;
[gabi@naomi:/home/gabi/swdev/pthread]
$ more ptt.c
#include <pthread.h>
#include <stdio.h>

#define NUM_THREADS  3
#define TCOUNT 10
#define COUNT_LIMIT 12

int count = 0;
int thread_ids[3] = { 0, 1, 2 };
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *
inc_count (void *idp)
{
   int j, i;
   double result = 0.0;
   int *my_id = idp;

   for (i = 0; i < TCOUNT; i++)
   {
      pthread_mutex_lock (&count_mutex);
      count++;

      /*
       * Check the value of count and signal waiting thread when
condition is
       * reached.  Note that this occurs while mutex is locked.
       */
      if (count == COUNT_LIMIT)
      {
         pthread_cond_signal (&count_threshold_cv);
         printf ("inc_count(): thread %d, count = %d  Threshold
reached.\n",
                 *my_id, count);
      }
      printf ("inc_count(): thread %d, count = %d, unlocking mutex\n",
              *my_id, count);
      pthread_mutex_unlock (&count_mutex);

      /* Do some work so threads can alternate on mutex lock */
      for (j = 0; j < 1000; j++)
         result = result + (double) random ();
   }
   pthread_exit (NULL);
}

void *
watch_count (void *idp)
{
   int *my_id = idp;

   printf ("Starting watch_count(): thread %d\n", *my_id);

   /*
    * Lock mutex and wait for signal.  Note that the pthread_cond_wait
    * routine will automatically and atomically unlock mutex while it
waits.
    * Also, note that if COUNT_LIMIT is reached before this routine is
run by
    * the waiting thread, the loop will be skipped to prevent
pthread_cond_wait
    * from never returning.
    */
   pthread_mutex_lock (&count_mutex);
   while (count < COUNT_LIMIT)
   {
      pthread_cond_wait (&count_threshold_cv, &count_mutex);
      printf ("watch_count(): thread %d Condition signal received.\n",
*my_id);
   }
   pthread_mutex_unlock (&count_mutex);
   pthread_exit (NULL);
}

int
main (int argc, char *argv[])
{
   int i, rc;
   pthread_t threads[3];
   pthread_attr_t attr;

   /* Initialize mutex and condition variable objects */
   pthread_mutex_init (&count_mutex, NULL);
   pthread_cond_init (&count_threshold_cv, NULL);

   /*
    * For portability, explicitly create threads in a joinable state
    * so that they can be joined later.
    */
   pthread_attr_init (&attr);
   pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_JOINABLE);
   pthread_create (&threads[0], &attr, inc_count, (void *)
&thread_ids[0]);
   pthread_create (&threads[1], &attr, inc_count, (void *)
&thread_ids[1]);
   pthread_create (&threads[2], &attr, watch_count, (void *)
&thread_ids[2]);

   /* Wait for all threads to complete */
   for (i = 0; i < NUM_THREADS; i++)
   {
      pthread_join (threads[i], NULL);
   }
   printf ("Main(): Waited on %d  threads. Done.\n", NUM_THREADS);

   /* Clean up and exit */
   pthread_attr_destroy (&attr);
   pthread_mutex_destroy (&count_mutex);
   pthread_cond_destroy (&count_threshold_cv);
   pthread_exit (NULL);
}
==========================================================================

Here is the gdb log:
==========================================================================
$ gdb ./ptt
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you
are welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for
details.
This GDB was configured as "powerpc-ibm-aix5.1.0.0"...
(gdb) break ptt.c:89
Breakpoint 1 at 0x10000814: file ptt.c, line 89.
(gdb) run
Starting program: /home/gabi/swdev/pthread/ptt
inc_count(): thread 0, count = 1, unlocking mutex
inc_count(): thread 0, count = 2, unlocking mutex
inc_count(): thread 0, count = 3, unlocking mutex
inc_count(): thread 0, count = 4, unlocking mutex
inc_count(): thread 0, count = 5, unlocking mutex
inc_count(): thread 0, count = 6, unlocking mutex
inc_count(): thread 0, count = 7, unlocking mutex
inc_count(): thread 0, count = 8, unlocking mutex
inc_count(): thread 0, count = 9, unlocking mutex
inc_count(): thread 0, count = 10, unlocking mutex
[Switching to Thread 1]

Breakpoint 1, main (argc=1, argv=0x2ff22810) at ptt.c:89
89         pthread_create (&threads[2], &attr, watch_count, (void *)
&thread_ids[2]);
(gdb) info threads
Illegal instruction(coredump)
==========================================================================

The following system libraries versions are installed on the 2 machines:
bos.rte.libpthreads       5.3.0.40
bos.rte.libpthreads       5.2.0.0

Is this a known issue ?
Any special flags that i need to use during the program compilation?

	gabriel