copying boost::exception across threads crashing

Below sample code to copy/transfer boost::exception object from 1
thread to another crashes due to a race condition during destruction
of exception/exception_ptr internal state. I am not sure what is the
best way to resolve it.

The boost version used was 1.42 and platform is Ubuntu lucid running
on a dual core Intel m/c. The compiler was gcc 4.4.3.

#include <iostream>

#include <boost/exception/all.hpp>
#include <boost/thread.hpp>

struct Exception
     : public virtual std::exception
     , public virtual boost::exception
{
};

struct MyException : public virtual Exception {};

struct MyTag {};

typedef boost::error_info<MyTag, std::string> MyError;

struct Test
{
     Test()
     {
         _t.reset(new boost::thread(boost::bind(&Test::executor,
this)));
     }

     ~Test()
     {
         _t->join();
     }

     void executor()
     {
         std::cerr << "executor: starting ...\n";
         for (;;)
         {
             boost::unique_lock<boost::mutex> lk(_mx);
             while(_q.empty())
             {
                 _cv.wait(lk);
             }
             {
                 boost::shared_ptr<boost::promise<int> > pt =
_q.front();
                 _q.pop_front();
                 lk.unlock();
                 pt->set_exception(boost::copy_exception(MyException()
<< MyError("test")));
             }
         }
     }

     void run_impl()
     {
         try
         {
             boost::shared_ptr< boost::promise<int> > pm(new
boost::promise<int>());

             boost::unique_future<int> fu = pm->get_future();
             {
                 boost::unique_lock<boost::mutex> lk(_mx);
                 _q.push_back(pm);
                 pm.reset();
             }
             _cv.notify_one();

             fu.get();
             assert(false);
         }
         catch (const MyException& e)
         {
             throw;
         }
         catch (const boost::exception& )
         {
             assert(false);
         }
         catch (...)
         {
             assert(false);
         }
     }

     void run()
     {
         std::cerr << "run: starting ...\n";
         for (;;)
         {
             try
             {
                 run_impl();
             }
             catch (...)
             {
             }
         }
     }

private:

     boost::mutex _mx;
     std::list< boost::shared_ptr< boost::promise<int> > > _q;
     boost::shared_ptr<boost::thread> _t;
     boost::condition_variable_any _cv;
};

int main()
{
     Test test;
     test.run();
}

/*
#0 0x080526bd in
boost::exception_detail::refcount_ptr<boost::exception_detail::error_info_container>::release
(this=0x806e26c) at /boost_1_42_0/boost/exception/exception.hpp:
79
#1 0x0804f7c5 in ~refcount_ptr (this=0x806e26c, __in_chrg=<value
optimized out>) at /boost_1_42_0/boost/exception/exception.hpp:
34
#2 0x0804bb61 in ~exception (this=0x806e268, __in_chrg=<value
optimized out>) at /boost_1_42_0/boost/exception/exception.hpp:
254
#3 0x0805579a in ~clone_impl (this=0x806e260, __in_chrg=<value
optimized out>, __vtt_parm=<value optimized out>) at /boost_1_42_0/
boost/exception/exception.hpp:391
#4 0x001ff633 in ?? () from /usr/lib/libstdc++.so.
6
#5 0x0027233d in _Unwind_DeleteException () from /lib/libgcc_s.so.
1
#6 0x001fe110 in __cxa_end_catch () from /usr/lib/libstdc++.so.
6
#7 0x0804f7a4 in Test::run (this=0xbffff74c) at ex_org.cpp:
89
#8 0x0804b869 in main () at ex_org.cpp:106
*/

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