Subject: SDL-News: non-blocking external DB access from within a process
From: Flávio J. Moritz Jr. (flavio.moritz#digitro.com.br)
Date: Fri Aug 13 1999 - 14:31:30 GMT
The originator of this message is responsible for its content.
-----From "=?iso-8859-1?Q?Fl=E1vio_J._Moritz_Jr.?=" <flavio.moritz#digitro.com.br> to sdlnews -----
Still on this "attempt to do non-blocking database access" thing.
How about, on a task, in a SDL process, inserting C-code to create another
thread of execution, responsible for an external database query, which upon
completion (of the thread and query, of course) changes the value of a SDL
process variable, which in turn is part of a SDL enabling condition ?
As a result, the SDL process in question is going to stay in a state waiting
for the enabling condition, while the rest of the SDL system will go on and
the thread will consult the database and change the enabling condition.
It seems to work! But Telelogic implements enabling condition in two ways:
- If it as now, import or view, it'll check the enabling condition very
often. A major overhead then.
- If it doesn't contain one of the above, it'll check the enabling condition
on every transition.
So, to avoid overhead, it'll be necessary to set a timer on that process to
force a transition and checking of the enabling condition.
What you people think about this ?
Could you follow my thoughts ?
Any flaws on it ?
[]'s Flavio.
> -----Original Message-----
> From: Flávio J. Moritz Jr. [mailto:flavio.moritz#digitro.com.br]
> Sent: Friday, August 13, 1999 9:46 AM
> To: 'sdlnews#sdl-forum.org'
> Subject: RE: SDL-news: On implementations
>
>
> Sure, Yoni.
> We do exactly the same thing here.
> But, lets get back to the database access problem.
> Let's say the SDL application wants to make a query on a
> table stored in a MySQL, PostgreSQL or even Oracle database server.
> I can't see how I can use the environment functions to make
> this query without blocking the whole SDL system.
> Because this query will actually be a function call. The
> application will return from this function call only after
> completion of the query.
> So, things would work this way:
> - The SDL process wants to make a query on a DB server, thus
> sending a signal to the environment;
> - xOutEnv is called by the SDT main loop to handle this signal;
> - In xOutEnv, a function from the database client API is
> called to handle the query;
> - Query takes a lot of time, meanwhile the SDL system is
> freezed on a DB client API function call.
> So I was wondering if I could put this DB function call on a
> separate thread and use SDL_Output to send a signal from this
> thread to the original thread informing query completion.
> But people at Telelogic told me that SDL_Output is not
> thread-safe. They said:
> -- quote ---
> "The solution is to implement a message sending/receiving
> protocol between your database thread and the SDLthread. The
> protocol should use XInEnv and XOutEnv to send/receive
> signals to the SDL system."
> -- end quote ---
> Well, that's exactly how we do it now and I tell you, it's
> really boring to write this "middleware".
> Unfortunately, I see no exit signal here. Thats the way it
> has to be done.
> Oh, it just occured to me that a thread for you could be
> different from a thread for me.
> I'm talking about POSIX threads on UNIX OS processes.
> A child thread shares most of the data from its parent
> thread, while a child process doesn't.
>
> Well, anyway, it's wonderful to see that I finally found a
> place to discuss this kind of things.
> Thanks.
>
> []'s Flavio
>
> > -----Original Message-----
> > From: owner-sdlnews#sdl-forum.org
> > [mailto:owner-sdlnews#sdl-forum.org]On
> > Behalf Of Yoni Rabinovich
> > Sent: Friday, August 13, 1999 5:49 AM
> > To: 'Fl?vio J. Moritz Jr.'; sdlnews#sdl-forum.org
> > Subject: RE: SDL-news: On implementations
> >
> >
> > The originator of this message is responsible for its content.
> > -----From Yoni Rabinovich <YRABINOV#teledata.co.il> to
> sdlnews -----
> >
> > Hi Flavio,
> >
> > I developed a fairly large telecom application a few
> years ago with
> > Telelogic's SDT (the SDL core of TAU).
> > The way we handled issues like those you raise were by using the
> > "environment" functions (xInEnv, xOutEnv etc.)
> >
> > The xInEnv function is called as part of the main loop of the SDT
> > scheduler. Our SDT application ran on top of the pSOS Real
> > Time OS, as a
> > pSOS task (thread). External applications generated pSOS
> > events when they
> > wanted to pass data to the SDL system. The SDT main loop
> > would check for
> > such events in xInEnv, and translate them into SDL signals
> > sent into the
> > system. We designed it such that the SDL system would not
> > block waiting for
> > inputs from the external applications, so as not to block the
> > SDL system
> > itself. On the other hand, the SDT task would "go to sleep"
> > if there was
> > nothing for it to do (i.e. no internal SDL signals or timers
> > or external
> > events pending).
> >
> > Regards,
> >
> > Yoni Rabinovitch
> > R&D Team Leader
> > ADC Teledata Communications
> > 7 Ha'sadnaot St, Hertzlia, 46120, Israel
> > email: yrabinov#teledata.co.il
> > Phone: +972-9-9591741
> > Fax : +972-9-9591444
> >
> > > -----Original Message-----
> > > From: flavio.moritz#digitro.com.br
> > [SMTP:flavio.moritz#digitro.com.br]
> > > Sent: 12 August 1999 22:14
> > > To: sdlnews#sdl-forum.org
> > > Subject: SDL-news: On implementations
> > >
> > > The originator of this message is responsible for its content.
> > > -----From "=?iso-8859-1?Q?Fl=E1vio_J._Moritz_Jr.?="
> > > <flavio.moritz#digitro.com.br> to sdlnews -----
> > >
> > > Hi,
> > >
> > > I've been lurking on this list for a while now and
> haven't seen any
> > > discussion on SDL tools.
> > > Well, I not actually interested in talking about the tool
> > itself, but
> > > rather
> > > how people use these tools.
> > > Let me give you an example.
> > > I use Telelogic's tools (TAU) to design telecom applications.
> > > It's (Telelogic's) C code generator implements the application.
> > > Those applications are compiled and run on UNIX boxes.
> > > Whenever I need to access a database server, I use interprocess
> > > communications protocols to send messages to another UNIX
> > process which in
> > > turn uses the database API.
> > > Just because I don't want my "SDL" app to block on a
> > function call while
> > > waiting for the database server.
> > > So, I was wondering. How does anybody else do the same thing ?
> > > How about shrinking this "middleware" into a thread ?
> > > Wouldn't it be better ?
> > > Can you see the kind of conversations I would like to have ?
> > > Is this an appropriate forum for this ?
> > > Can I start this kind of discussions here?
> > > Does anybody knows a better forum for this?
> > > Any mailing lists or newsgroups ?
> > >
> > > Please, don't take me wrong. I find people here very
> > helpful. I just don't
> > > want to bother you with things that aren't of your interest.
> > >
> > > []'s Flávio Moritz
> > >
> > > "The chase is better than the catch."
> > >
> > >
> > > -----End text from "=?iso-8859-1?Q?Fl=E1vio_J._Moritz_Jr.?="
> > > <flavio.moritz#digitro.com.br> to sdlnews -----
> > > Join http://www.sdl-forum.org/Society/members.htm for extra
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> >
> > -----End text from Yoni Rabinovich <YRABINOV#teledata.co.il>
> > to sdlnews -----
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>
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