Re: [Boost-users] shared_ptr use_count in multi threaded environment

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-04-14 12:50:26

Manges, Ross G wrote:
> I've been experiencing trouble with shared_ptrs in a multithreaded
> environment.  First, I noticed that the ref count wasn't being locked
> when updated by multiple threads (shared_count.hpp).  I recompiled the
> boost library with BOOST_HAS_THREADS defined the user.hpp, and now I
> can verify that the scoped_lock is being used, but I'm still seeing
> the same kind of problems.  The traces happen in different places
> each time, but in general it appears that the ref count is being
> decremented to zero inappropriately, which in turn sometimes causes
> the dreaded "assert px != 0" message.  See the example traces below.
> Please let me know if you have any suggestions on how I might proceed
> to debug this problem. Thanks!

Two questions:

- Is it possible that some parts of your code are compiled without 
BOOST_HAS_THREADS?

> #5  0xb73aac18 in boost::shared_ptr<Connector>::operator= (
>    this=0xb65e0ce4, r=@0xb6c01b18) at shared_ptr.hpp:148
> #6  0xb73a974e in Listener::run (
>    this=0xb6c02f68) at Adapter.cpp:966

- Is it possible that you are assigning to the shared_ptr<Connector> object 
and at the same time reading it (making a copy of it, for example) or even 
assigning or resetting it from a different thread?