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

Steve Huston shuston at riverace.com
Wed Feb 20 15:24:08 CST 2008 

Hi Gonzalo,

> Excellent, thanks Steve.

You're welcome.

> In fact, I am pretty sure this is exactly what
> I had done once, a long time ago, and also due to your suggestion; I
> believe this is what sounded to me similar to what Ganesh was 
> proposing.

Ok, good.

> Two questions:
> 
> 1. Will this work with the TP_Reactor? I mean, when the strategy
> notifies the reactor, will all threads in the reactor 
> eventually be used to handle the notifications?

There's no guarantee that "all" threads will be used, and you should
double-check what affect the "owner" concept has here. But, yes,
notifications work with the ACE_TP_Reactor.

> 2. Will this work on Win32, with / without the TP_Reactor?

Yes, but take note of the caveat re ownership for ACE_WFMO_Reactor in
the ACE Knowledge Base.

-Steve


> On Wed, 2008-02-20 at 15:59 -0500, Steve Huston wrote:
> > Check out ACE_Reactor_Notification_Strategy. There's also an
> > explanatory piece in the ACE Knowledge Base at
> > http://www.riverace.com/ace-kb.htm - search for "notifications"
> > 
> > Best regards,
> > -Steve
> > 
> > --
> > Steve Huston, Riverace Corporation
> > Want to take ACE training on YOUR schedule?
> > See http://www.riverace.com/training.htm
> > 
> > 
> > > -----Original Message-----
> > > From: ace-users-bounces at cse.wustl.edu 
> > > [mailto:ace-users-bounces at cse.wustl.edu] On Behalf Of Gonzalo
> > Diethelm
> > > Sent: Wednesday, February 20, 2008 3:41 PM
> > > To: Ganesh Pai
> > > Cc: ace-users at cse.wustl.edu
> > > Subject: Re: [ace-users] Basic Reactor concepts
> > > 
> > > 
> > > Thanks Ganesh. The approach you state rings a bell with me, I 
> > > am sure I
> > > have done something similar. Could this be done without having
the
> > > pipes, and only an event handler for each queue? The, when 
> > > messages are
> > > deposited on the queue, could I achieve the same result by 
> > > just calling
> > > reactor->notify(event_handler)? Or are the separate pipes a
must?
> > > 
> > > Thanks and best regards.
> > > 
> > > On Wed, 2008-02-20 at 15:11 -0500, Ganesh Pai wrote:
> > > > Here is how I have solved this problem. This approach is 
> > > for reactors based
> > > > on select/poll/epoll + Leader Follower pattern.
> > > > 
> > > > * For each of the N queues, associate a pipe + event handler 
> > > > * Plug the event handler into the reactor
> > > > * Using TP reactor you could then have M threads which run the
> > > >   Reactor loop
> > > > * Whenever messages are deposited into the queues, the 
> associated 
> > > >   pipe has to be notified
> > > > * One of the M threads would handle the pipe (handle_input) 
> > > and process
> > > >   the message from the associated queue
> > > > 
> > > > Hope this helps. The key to the above approach was the 
> > > understanding that
> > > > select works only on some I/O handle. By associating a 
> > > notification handle
> > > > (pipe) with each work queue makes the TP reactor now a 
> > > de-multiplexer for
> > > > message queues as well.
> > > > 
> > > > 
> > > > -----Original Message-----
> > > > From: ace-users-bounces at cse.wustl.edu
> > > > [mailto:ace-users-bounces at cse.wustl.edu] On Behalf Of 
> > > Douglas C. Schmidt
> > > > Sent: Wednesday, February 20, 2008 2:13 PM
> > > > To: Gonzalo Diethelm
> > > > Cc: ace-users at cse.wustl.edu
> > > > Subject: Re: [ace-users] Basic Reactor concepts
> > > > 
> > > > 
> > > > 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
> > > > 
> > > > _______________________________________________
> > > > ace-users mailing list
> > > > ace-users at mail.cse.wustl.edu
> > > > http://mail.cse.wustl.edu/mailman/listinfo/ace-users
> > > > 
> > > > 
> > > 
> > > -- 
> > > Gonzalo Diethelm
> > > gonzalo.diethelm at diethelm.org
> > > 
> > > _______________________________________________
> > > ace-users mailing list
> > > ace-users at mail.cse.wustl.edu
> > > http://mail.cse.wustl.edu/mailman/listinfo/ace-users
> > > 
> > 
> > 
> > 
> 
> -- 
> Gonzalo Diethelm
> gonzalo.diethelm at diethelm.org
>

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