Re: [boost] Thread library/extensions question

From: William E. Kempf (wekempf_at_[hidden])
Date: 2003-01-27 11:04:38

Alisdair Meredith said:
> In view of the pending comittee meeting, and knowing those involved will
> be wanting to tie down any loose ends, I'm going to ask a thread-related
> question which relates as much to language support (I think) as boost
> thread, but this seems to be the active place for threads/ISO at the
> moment (please correct me if wrong)
>
> I am going through our logging code again as we now have competing
> requirements and more rigorous requests for thread support.  Currently
> our logging goes through a singleton implementation (provided by Andrei
> and the Loki library, thanks Andrei) but I would like to move to what I
> would describe as 'singleton-per-thread'.
>
> The neat thing about singletons (or at least this implementation) is
> that they exist for the lifetime of the process, potentially created
> before main and destructed only after main has exited.  I would like a
> similar facility on a per-thread basis (tied to each thread's stack)
> This would allow me to log from multiple threads without having to lock
> the logger object, and without interspersing each threads messages
> throughout the same log.
>
> Is such an implementation possible with the current boost::thread, and
> is such an implementation currently under consideration in the lagnuage
> extension TR wrt thread support?

Yes, this is trivially implemented with boost::thread_specific_ptr<>. 
Well, it may require the use of boost::once() as well, which complicates
things a little, but it's not that bad.  As for language extensions,
that's still being thought on.

> It would seem 'obvious' to me that I would want to create each logger
> object in the stack of each thread, rather than as part of the parent
> thread object owned by the thread creating the child-thread.  I also
> believe this logger example could quite easily be generalised to a whole
> group of designs that want per-thread 'singletons', but the logger makes
> a fairly clean example.

Creating the singleton on the "stack" will require a bit more effort
(possibly with a function object adapter to create the instance?), but is
still feasable.

William E. Kempf
wekempf_at_[hidden]