RE: [boost] Re: [Threads] Simple active object wrapper, take 2

From: Hurd, Matthew (hurdm_at_[hidden])
Date: 2004-02-23 19:00:16

> On Behalf Of Matthew Vogt
> Subject: [boost] Re: [Threads] Simple active object wrapper, take 2
> 
> > scott <scottw <at> qbik.com> writes:
> 

Had a little thought that might be relevant.  Please spank me if this is
OT given the rather specific implementation I'm dropping in on...

As mentioned previously, future values could give you a lazy way of
evaluating the result, even when you aren't multithreaded.

In the truly "active" object, that is, it has at least one thread, you
could call the methods with a future instead of a normal value so that
when the result arrives it percolates through the implied queue. 

Now for a new thought.  What about using an expression template
mechanism so that when you combine futures they are glommed at compile
time to remain lazy?

boost::future<double> sum = some_thing_maybe_active.total();
boost::future<double> count = some_thing_maybe_active.count();
boost::future<double> average = sum / count;

sum / count forms a lazy expression

if a method groks a future and then this becomes interesting...

boost::future<double> result =
some_thing_maybe_active.do_stuff(average);

You can end up with the active object percolating all the way through to
"result" without any blocking until the result of "result" is used.

If you get rid of the thread(s) in the active object idea, you end up
with a mechanism for lazy evaluation.

Perhaps there is a more general mechanism / pattern and bike shop name
lurking in this pattern...

Regards,

Matt Hurd
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Susquehanna Pacific P/L
hurdm_at_[hidden]
+61.2.8226.5029
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