[Ace-users] [ace-users] Basic Reactor concepts

Gonzalo Diethelm gonzalo.diethelm at diethelm.org
Wed Feb 20 14:43:47 CST 2008

Hi Doug,

Ok, from what you say I understand the Reactor is specifically geared
for OS event handling, although it COULD be used to dispatch other types
of events.

Is there a specific class in ACE that implements the
Half-Sync/Half-Async pattern in a way that is usable for something like
I have described? A simple grep does not find any occurrence of "half"
that looks promising...

Thanks and best regards.

On Wed, 2008-02-20 at 13:12 -0600, Douglas C. Schmidt wrote:
> Hi Gonzo,
> > Again, I am trying to lessen my ignorance here...
> Always a laudable goal ;-)
> > Although I have always seen the Reactor as a key piece in the Acceptor
> > / Connector / Svc_Handler class family in ACE, used to process I/O, a
> > Reactor seems to be a generic concept for solving the following
> > requirement, right?
> > 
> > "Decouple the reception of events from its processing, in a way that,
> > for instance, makes it possible to receive events in one thread and
> > process them in a different thread".
> This is actually a different set of POSA2 patterns, e.g.,
> Half-Sync/Half-Async or Active Object.  You should start by reading
> about them.  The Reactor pattern can be used as part of the
> implementation of Half-Sync/Half-Async pattern.
> > Now, for me to understand this better, let me pose an example to you and
> > maybe someone can indicate, if I am correct, how such an example would
> > be handled with a Reactor. Say I have N message queues; they are all
> > filled via some kind of opaque process which does not concern us, except
> > for the fact that each queue is filled totally independent from the
> > others (for example, one queue could store mouse events, another could
> > store serial port incoming data, etc.). Now, I wish to have M threads
> > (M != N) running in parallel, with an identical, simple infinite loop
> > that will fetch an event from a queue that has signalled it has events
> > available, and then process this event.
> > 
> > If I am right in my assumptions about the Reactor's purpose in life, 
> This isn't really the Reactor's purpose in life, unless those N queues
> happen to be the appropriate type of OS handle than can be waited upon
> together via a "synchronous event demuxer".
> > how do I wire things in this scenario in order to have the N queues
> > use a Reactor to notify the M threads for processing?
> I think you're better off using the Half-Sync/Half-Async pattern here,
> so please start by looking at it first.
> Thanks,
>         Doug

Gonzalo Diethelm
gonzalo.diethelm at diethelm.org

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