From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Dave Baggett" <dmb@itasoftware.com>
To: <pthreads-win32@sourceware.cygnus.com>
Subject: Bug report with source code attached
Date: Tue, 29 Feb 2000 23:59:00 -0000
Message-id: <021401bf8353$6f755d30$0903a8c0@itasoftware.com>
X-SW-Source: 2000/msg00015.html

I have a sizeable pthreads-based server application that works well under
Linux and NT (using pthreads-win32). Under NT, however, it crashses
periodically. After several days of debugging, I have isolated the source of
the crashes to a small bit of code (included below) which looks to me to be
perfectly innocent. However, I may not understand pthreads semantics
adequately  -- it wouldn't be the first time --  so my code might be wrong.

If I compile the program below and run it with a "-l" argument ("l" as in
"lose"), I get:

  The instruction at "0x7800d557" referenced memory at "0x00000170".
  The memory could not be "written".

This happens after a delay that varies between 0 and 15 minutes.  The
instruction address never varies, but the referenced memory location
does. The debugger shows that it's dying in the malloc call in
pthread_attr_init. I.e., the heap is somehow getting corrupted.

If I run it without "-l", it seems to be able to run for hours without
crashing. Am I correct in assuming that the two modes of operation should
be equivalent (aside from the fact that I might be leaking memory by
not freeing the attrs)?

This happens with the 1999-11-02 snapshot as well as the 1999-09-17
snapshot.

I see nothing in the win32-pthreads source that looks like it could cause this.
However, I did notice that pthread_attr_init() returns you an attr that sets
the stacksize to 1K, which doesn't seem good. Explicitly setting the stacksize
won't fix the crash problem, but it still seems like you ought to default the
stack to 256K or something reasonable.

Apologies in advance if I'm just doing something stupid. :)

Dave Baggett
dmb@itasoftware.com
-------------------------------------------------------------------------------
//
// Call with -l argument to cause a crash.
// Compiled with MSVC6 using these args:
//   -nologo -D WIN32 -D _WINDOWS -ML -MTd -GX -Od -G6 -W3 -Zi
//
#include "pthread.h"
#include <assert.h>

void *NOP(void *p) { return NULL; }

int
main(int argc, char **argv)
{
    bool lose = (argc == 2 && !strcmp(argv[1], "-l"));
    for (;;) {
        int retval;
        pthread_t tid;

        if (lose) {
            pthread_attr_t attr;
            retval = pthread_attr_init(&attr);
            assert(retval==0);          // success
            retval = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
            assert(retval==0);          // success
            retval = pthread_create(&tid, &attr, NOP, NULL);
            assert(retval==0);
        }
        else {
            retval = pthread_create(&tid, NULL, NOP, NULL);
            assert(retval==0);          // success
            retval = pthread_detach(tid);
            assert(retval==0);
        }
    }
    return 0;
}