Subject: Re: SDL-News: On implementations
From: Vibhor Agarwal (vibhor#lucent.com)
Date: Mon Aug 16 1999 - 04:47:53 GMT
The originator of this message is responsible for its content.
-----From Vibhor Agarwal <vibhor#lucent.com> to sdlnews -----
Yoni/Flavio,
I thought of doing this as described in first paragraph by Yoni..The SDL process A
requiring to make a database query would send a signal to process B (running in its own
thread and interfacing with database using APIs) and go to a waiting state. When it gets
response from B through a signal, it would move to next transition.
So what is it...Can the process B send signals to all such process A1..An , in a thread
safe manner...
Regards,
Vibhor
Yoni Rabinovich wrote:
> The originator of this message is responsible for its content.
> -----From Yoni Rabinovich <YRABINOV#teledata.co.il> to sdlnews -----
>
> Hmmm, what about defining an SDL process which handles the interaction with
> the database, and runs in its own thread ? This process would receive an SDL
> signal from another SDL process, whenever the database needs to be queried.
> It would then make the call to the database API in an SDL task. Upon
> returning from the database API, it would send back an SDL signal with the
> data retrieved from the database (with OUTPUT TO Sender).
>
> Are you saying that this SDL process won't be able to send SDL signals to
> other SDL processes in different threads via SDL_Output in a thread-safe
> manner ?
>
>
>
> > 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 Fl?vio 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 -----
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> > >
> > > -----End text from Yoni Rabinovich <YRABINOV#teledata.co.il>
> > > to sdlnews -----
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> > >
> >
> >
> > -----End text from "=?iso-8859-1?Q?Fl=E1vio_J._Moritz_Jr.?="
> > <flavio.moritz#digitro.com.br> to sdlnews -----
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>
> -----End text from Yoni Rabinovich <YRABINOV#teledata.co.il> to sdlnews -----
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-----End text from Vibhor Agarwal <vibhor#lucent.com> to sdlnews -----
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