Re: [Boost-users] Flyweight

From: Jens Seidel (jensseidel_at_[hidden])
Date: 2008-01-31 03:50:15

On Wed, Jan 30, 2008 at 06:38:34PM +0100, Joaquín Mª López Muñoz wrote:
> Jens Seidel ha escrito:
> > On Wed, Jan 30, 2008 at 01:41:15PM +0000, Martin Fisher wrote:
> > > Using the boost_1_35_0 svn library download and Visual C++ 2008 Express
> > > edition.
> > > Originally compiled as a CLR program.  Recompiling using native Win32
> > > still gives a crash during program termination - in
> > > atomic_count_win32.hpp in operator-- (BOOST_INTERLOCKED_DECREMENT)
> > > Unhandled exception at 0x010752b9 in fly2.exe: 0xC0000005: Access
> > > violation writing location 0x00779040.
> >
> > There is indeed a bug somewhere. I could reproduce it on Linux which
> > doesn't suffer from CLR/libc/... mess. I just compiled it (code from
> > trunk) and it crashes. valgrind reports:
> 
> I could also reproduce it here, and found the reason for the crash. Please
> follow me:
 
> And this is the problem: when the factory is destroyed, there are still
> flyweight objects around (those in vec), when there should be none,
> and on vec's destruction time the flyweight objects point to deallocated
> memory, hence the crash.
> 
> This is solved by forcing boost::flyweight<string> static initialization
> before that of vec:
> 
>   boost::flyweights::flyweight<string>::initializer init;
>   vector<boost::flyweights::flyweight<string> > vec;
> 
> So that static initialization order is correct. Could you please try the fix?

Right. valgrind does no longer complain.
 
> This is a fundamental issue for which I see no easy *automatic* fix upon first
> reflection, other than documenting very clearly the situations in which it
> can arise. Comments and suggestions welcome.

Maybe it is possible to add an assert somewhere, so that at least
debugging is simplified? Not everyone reads documentation carefully.

Thanks,
Jens