Re: [dbus-cplusplus-devel] Ref counter system not thread safe?

[Nicolas P. <npa...@wy...>]

On Thursday 20 November 2008 12:43:16 P. Durante wrote:
> Hi Nicolas,
>
> On Thu, Nov 20, 2008 at 10:22 AM, Nicolas Parcollet
>
> <npa...@wy...> wrote:
> > I everybody. I m occasionnaly working with DBus C++ and pushing it to its
> > highest limits.
>
> that's very much needed and very appreciated, thanks
>
> > The following traces show a failure condition that happens sometime when
> > I ran a very long test making heavy use of DBus C++. The program contains
> > one adaptor and several proxies. It is a threaded environment.
> >
> > Program received signal SIGBUS, Bus error.
> > [Switching to thread 1546]
> > 0x004178c8 in DBus::RefCnt::noref (this=0x45c4a8)
> > at
> > /usr/targets/081119-1.1.13-debug/root/usr/include/dbus-c++-1/dbus-c++/uti
> >l.h:72 72                      return (*__ref) == 0;
> > (gdb)
> > Continuing.
> > Program terminated with signal SIGBUS, Bus error.
> > The program no longer exists.
> > (gdb)
> >
> > It seems the the ref counter is broken. This is probably due to a race
> > condition between unref/noref but it is still quite blur for me. From
> > what i saw the ref counting sytem is not thread safe. Any idea how this
> > could be solved?
>
> off the top of my head, the reference counting variable should be
> declared 'volatile', after that the compiler should be smart enough to
> use atomic intrinsics when incrementing/decrementing the counter, i'll
> change that now
>

I will try the volatile solution since i need a quick fix. Beside this, I got 
some more infos. I don't see where the operator!= comes from.

(gdb) info threads
* 1 thread 2022  0x004177c0 in DBus::RefCnt::noref (this=0x45c4a8)
    
at /usr/targets/081119-1.1.13-debug/root/usr/include/dbus-c++-1/dbus-c++/util.h:72

(gdb) bt
#0  0x004177c0 in DBus::RefCnt::noref (this=0x45c4a8) 
at /usr/targets/081119-1.1.13-debug/root/usr/include/dbus-c++-1/dbus-c++/util.h:72
#1  0x29678026 in __gnu_cxx::operator!=<std::string*, std::vector<std::string, 
std::allocator<std::string> > > ()
   from /usr/targets/current/root/usr/lib/libdbus-c++-1.so.0
#2  0x2967807c in __gnu_cxx::operator!=<std::string*, std::vector<std::string, 
std::allocator<std::string> > > ()
   from /usr/targets/current/root/usr/lib/libdbus-c++-1.so.0
#3  0x7bc87cd8 in ?? ()
#4  0x7bc87cd8 in ?? ()

(gdb) print this->__ref
$8 = (int *) 0x6433f379

(gdb) print *(this->__ref)
Cannot access memory at address 0x6433f379


> > I am working with version 0.5 (AC_INIT([libdbus-c++], 0.5.0,
> > [sh...@gm...])). Since the ChangeLog is not up to date i can't
> > figure out if something like that was fixed or not, so I need your help.
>
> due to lack of active maintainership (blame me), there has never been
> an official release, 0.5.0 could refer to any git snapshot taken in
> the past months, I recommend using the latest source from freedesktop
> git clone git://anongit.freedesktop.org/git/dbus/dbus-c++/
>

It is actually a version of november 2007. Not sure it was on freedesktop 
already. Unfortunately i can't change the version like that.

> > Thanks a lot.
> >
> > Nico P.
>
> thank you,
> Paolo

Anyway thanks for your fast reply. 

Nico P.

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