m_ioService.post(m_strand.wrap( boost::bind(&LogWriter::append, (*logWritersItr), _logMessage, _logLevelString) ));
The second param of Bind, (*logWritersItr), is a shared_ptr of LogWriter's subclass. The signature of LogWriter::append() is as following:
virtual void append(const std::string& _logMessage, const std::string& _logLevelString) = 0;
Base on document at http://www.boost.org/doc/libs/1_44_0/libs/bind/bind.html, the way I use bind will duplicate a copy of that shared_ptr. Any idea when will the duplicated shared_ptr become invalid so that the reference count decreases by one?
bind() takes your shared_ptr by value, so it won't become "invalid". After io_service executes your functor, it will be destroyed, so all its internal copies of that shared_ptr will be destroyed as well.