On Sep 23, 2010, at 9:59 AM, Shiou Ming Lee wrote:
On Thu, Sep 23, 2010 at 9:25 AM, Igor R
<boost.lists@gmail.com> wrote:
> 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?
After io_service executes your functor, it will be destroyed, so all
its internal copies of that shared_ptr will be destroyed as well.
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I think I don't quite completely understand functor.., is it by C++ that a functor will be destroyed automatically once executed? Or is this a feature from boost.bind?
I think that you're thinking too hard about this.
It's not a feature from boost.bind, it's just standard C++ lifetime rules.
1) The shared_ptr is copied into the bind object. (use count for the shared_ptr ++)
2) The bind object is passed (by value) to m_ioService.post. (use count for the shared_ptr++)
*) The original bind object gets destroyed (goes out of scope, whatever) (use count for the shared_ptr--)
*) When m_ioService.post returns, the copy of the bind object that was passed to it is destroyed (use count for the shared_ptr--)
the last two are '*'s rather than 3/4 since I don't remember the order (and it doesn't really matter, either). ;-)
If m_ioService.post makes copies of the functor and/or the shared pointer internally, then the use count for the shared pointer will be incremented for each copy, and decremented when a copy is destroyed.
-- Marshall