"vicente.botet" <vicente.botet@wanadoo.fr> writes:
----- Original Message ----- From: "Anthony Williams" <anthony_w.geo@yahoo.com> To: <boost@lists.boost.org> Sent: Wednesday, May 14, 2008 10:55 AM Subject: Re: [boost] Review Request: future library (N2561/Williams version)
"vicente.botet" <vicente.botet@wanadoo.fr> writes:
Why you don't allow multiple callbacks? I suposse that this is related to the implementation of do_callback
void do_callback(boost::unique_lock<boost::mutex>& lock) { if(callback && !done) { boost::function<void()> local_callback=callback; relocker relock(lock); local_callback(); } }
You need to call all the callbacks with the mutex unlock, and you need to protect from other concurrent set_wait_callback. So you will need to copy the list of callbacks before unlock.
Is this correct?
That is correct with respect to the implementation,
BTW, Braddock implementation do a move of the list of callbacks before doing the callbacks. What do you thing about this approach?
That's an interesting idea: rather than calling the callback every time some thread waits on a future, it's only called on the first call. You could make the callback clear itself when it was invoked if you want that behaviour, as the promise or packaged_task is passed in to the callback.
but I don't actually see the need for multiple callbacks. The callbacks are set as part of the promise or packaged_task. I can't imagine why that would require multiple callbacks. In any case, the user can provide that facility on their own if required.
What about the guarded schedule of Braddock? template future<T> schedule(boost::function<T (void)> const& fn, future<void> guard = future<void>()) { promise<T> prom; // create promise future_wrapper<T> wrap(fn,prom); guard.add_callback(boost::bind(&JobQueue3::queueWrapped<T>, this, wrap, prom)); return future<T>(prom); // return a future created from the promise }
Several task can be scheduled guarded by the same future.
That's a completion callback, not a wait callback. My proposal doesn't offer completion callbacks. Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL