[Ace-users] Re: [ace-bugs] [ACE_TP_Reactor]: [Event_Handler
suspension nothonoredfor handle_close]
hal.black at gmail.com
Thu Jul 26 23:18:13 CDT 2007
Thanks Doug, Johnny, and Steve all for your quick replies.
On 7/26/07, Steve Huston <shuston at riverace.com> wrote:
> Hi folks,
> As Doug and Johnny indicated, there were some important improvements
> to ACE_TP_Reactor a few betas ago, and 5.5.9 may resolve this. But I
> want to clarify a question Hal asked:
> > As I understand it, the ACE_TP_Reactor is supposed to
> > suspend events
> > on an event handler that is being called by another thread
> > until that call
> > returns. So what's going on here? Is this a mistaken
> > interpretation by me?
> Yes, a common one... ACE_TP_Reactor suspends the handler around _I/O_
> callbacks, but not around notifies or timers. Since you're using
> notify(), the suspension around your handle_input() callback is
Ahh, so that's why it looked like it didn't suspend notifies, timers, etc
when I was reading through the ACE_TP_Reactor source code. I just couldn't
fathom how the ACE_TP_Reactor would be useful at all without the locking:
there would be no safe way for general purpose event handlers being called
by the TP Reactor to self destruct (which is very widely used with
ACE_Event_Handlers). You guys do such a great and thorough job, I just
assumed I was missing something. 8')
The reference-counted event handler sounds like it will solve that problem,
though. I really should go through the back issues of the Riverace
Changing this comment from ACE_TP_Reactor.h might make this misconception a
bit less common, still:
* [...] Note that callback code in
* Event Handlers (e.g. Event_Handler::handle_input) does not have to
* be modified or made thread-safe for this Reactor. This is because
* an activated Event Handler is suspended in the Reactor before the
* upcall is made and resumed after the upcall completes. Therefore,
* one Event Handler cannot be called by multiple threads
> Is there a known bug in this version? Or is something else
> > entirely going on?
> You may also want to investigate using reference-counted event
> handlers, which would prevent deletion of the handler while there's a
> notify() queued, or any timer or I/O registrations still in effect.
> This is covered in the October 2005 edition
> (http://www.riverace.com/newsletters/October2005.htm) of the Riverace
> ACE News and Tips newsletter.
Great tip. Is ACE_Svc_Handler::handle_close() is safe to call? That is,
does it know about the reference counting and therefore won't self destruct
and mess up the reference counting scheme?
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