Re: Memory allocators / STL

[Benjamin Kosnik <bkoz at redhat dot com>]

> > There have been problems with using the pool allocators in a multithreaded
> > program; I've pointed you at an internal bug report (102997) about that a
> > couple of times.  I would think the test case from there should work for
> > you.  I was able to reproduce the bug on schitzo.

Huh.

> > Of course, that bug report is against a 2.95ish toolchain, so the problems
> > may have been fixed by now.

I tried it with gcc-3.1, on a dual RH 7.1 machine. It's fine. This is 
with the pool-alloc allocators.

Perhaps it's dual solaris 2.6, 2.95.x problem, or the older library. 


> If I can get access to this ``internal bug report (102997)'', then I
> would be happy to fix mainline gcc if the problem still exists there
> and I can reproduce it in my environment(s).  But I only want the test
> case if it is something that can be publicly posted.

Right. 

This testcase works now, but perhaps it can be modified into the unposted 
problem with mySQL, etc. 

// Compile with:
// g++  -g  -D_THREAD_SAFE -DSOLARIS -D_REENTRANT -D_PTHREADS -o \
//      bad_hash  bad_hash.cpp -lpthread

// Causes a core dump in the first few iterations under Solaris 2.6
// egcs 2.91.66 or Cygnus 98r2, STL library included with the
// respective distributions.
// The core dump does not happen with NUM_THREADS=1, and happens more
// quickly the higher the value for NUM_THREADS.
// There is no core dump if std::map is used instead of 
// std::hash_map, or if types other than string are used 
// for the map's value type (int, char*, vector do not cause 
// the core dump).
//
// John Panzer
// jpanzer@netscape.com

#include <cstdio>
#include <cstdlib>
#include <sys/poll.h>
#include <string>
#include <ext/hash_map>
#include <pthread.h>


using namespace std;

const int NUM_ITERATIONS=500000;

void *f(void *arg)
{
  for(int i = 0; i < NUM_ITERATIONS; ++i)
    {
      hash_map<int, string> m;
      m[42] = "foobar";
      poll(0, 0, 10);
    }
}

void mt_test()
{
  const int NUM_THREADS = 20;
  void* ret=0;
  pthread_t thread[NUM_THREADS];
  for(int i=0;i<NUM_THREADS;++i)
    pthread_create(&thread[i], NULL, f, (void*)i);
  for(int i=0 ; i < NUM_THREADS; ++i)
    pthread_join(thread[i], &ret);
}

int main()
{
  mt_test();
  return 0;
}