[saga-rg] SAGA strawman API: comments to Stream functions
Andre Merzky
andre at merzky.net
Fri Dec 2 12:59:09 CST 2005
Hi Thomas,
Quoting [Thomas Eickermann] (Dec 02 2005):
>
> Hi Andre,
>
> thanks for your answer. I agree with your comments that access
> to raw descriptors is somewhat problematic.
> Nevertheless i regard them as quite important for implementing
> real-life interactive applications. Two examples:
>
> 1. AVS/Express allows to trigger a module if an event occurs at a
> descriptor. I do not know of any other way to implement stream
> communication within AVS/Express and i imagine, that the situation
> is quite similar for other tools like OpenExplorer.
>
> 2. If you use some GUI toolkit (e.g. Qt), you can also register callbacks
> for events on descriptors. If such a descriptor is not available, the
> only thing you can probably do is to use timers and polling. There are
> obviously good reasons to avoid that, if possible.
I agree about the importance.
> See further comments inline.
>
> Best regards,
> Thomas
>
>
> Andre Merzky wrote:
> >Hi Thomas,
> >
> >sorry for the late answer... *sigh*
> >
> >
> >Quoting [Thomas Eickermann] (Nov 10 2005):
> >
> >>* in both use-cases there is an interactive visualisation/steering
> >> application sitting at one end of the stream. Such applications
> >> typically use some kind of GUI-toolkit with operates in an
> >> event-callback mode or similar, where callbacks can be registered
> >> for events occuring at socket/pipe/...-descriptors. On the other hand, in
> >> many implementations, a Stream will somehow use a socket, pipe or
> >> something else with a descriptor. Therefore we need a function that
> >> returns
> >> the descriptor associated to a stream:
> >> fd = descriptor(Stream);
> >
> >
> >This is complicated, as we do not know _if_ there will be a
> >native descriptor available, and if operations on that will
> >interfere with the implementation.
> >
> availability:
> right, i was somewhat unprecise. What i meant was the native
> respresentation of a socket in the given language (a descriptor
> in C, an IO::Socket obejct in Perl and probably there is something
> like that in most languages.
I was unprecise as well I guess: you are right, there'll be
a native representation in most languages, not doubt.
What I mean with availability is best shown in Globus-XIO:
I simply do not know _how_ I could obtain the native
descriptor from a globus-XIO based implementation: there is
no globus-xio call exposing the descriptor.
>> E.g. the implementation might be based on Globus-XIO or on
>> Reliable UDP. For the first I do not know if a descriptor
>> is availbale via the API, for the second there are two
>> descriptors (one tcp, one udp) the application would need to
>> handle.
>
> To handle the second case, 'descriptor' would have to return
> an array of descriptors. I don't see that in the first case
> an implementation could return something better than a NULL-array.
It is dependend on the middleware then: the application
needs to be aware of the fact that saga implementation
returns a single fd, but saga implementation returns 2 fd's,
with specific handling requirements.
I am not saying that this is impossible. Just would like to
be sure that this is the best way to go...
> >Also, the implementation might transparently add a protocol
> >(say checksumming), and direct tempering with the desfriptor
> >might very well break that protocol.
>
> I agree, the only thing the user is allowed to do with the
> descriptor, is to call 'select'. Read, write, seek, close
> would most likely break the protocol.
>
> However, this cannot be enforced, and i am aware that this
> conflicts the principle of hiding the implementation from
> the user (to minimize the risk that the user breaks something).
I checked with QT, and I think there is a way to handle
SAGA events in QT:
------------------------------------------------------------
// this be a callback for a saga stream object, which gets
// fired on new data arriving etc.
void my_saga_file::saga_cb (void)
{
emit update_gui ();
}
my_gui g;
my_saga s;
QObject::connect (&s, SIGNAL (update_gui (void)),
&g, SLOT (saga_cb (void)));
------------------------------------------------------------
(The code above is probably not really correct, but you get
the image...)
my_saga::saga_cb would need to registerd to saga as callback
for events on a stream. Then, if such an event occurs, the
callback would trigger (emit) a QT event (update_gui) which
would be received by your gui class, and cause, well, the
gui to update etc.
The QT event mechanism would allow to use any data available
in the callback (e.g. string read from the stream) to be
signalled to the gui loop as well.
So, would that fullfill your requirements?
Am am not so sure about AVS and other packages. I did not
work with AVS for quite some time, but IIRC, the events have
been coupled much tighter to selects on descriptors, with no
alternative rounds? However, for all other packages I know
(not many), a trivial (e.g. 3 line) translation from saga
callbacks to 'native' events seems to exist.
Cheers, Andre.
> >So, we might be able to add the API function, but it is
> >difficult to define what it should return in the cases
> >outlined above...
> >
> >
> >
> >>However, users have to be aware, that several Streams
> >>may share the same decriptor (e.g. in VISIT, if several
> >>Streams are tunneled through a single connection of a
> >>different protocol like ssh).
> >
> >
> >
> >>* a general remark on Streams: i like the idea of keeping the Stream-API
> >>close
> >> to the BSD socket API. However, as Andrei mentioned, we also often have
> >> to deal with more message- or block-oriented communication patterns.
> >> In the internal API the we use in the VISIT toolkit, we have therefore
> >> added a timeout parameter to all functions and slightly changed the
> >> semantics.
> >> For example
> >>
> >> nread = read(stream, buffer, size, timeout);
> >>
> >> works as: try to read size bytes from stream, return if either:
> >> - size bytes have been read, or
> >> - timeout seconds have passed (wait forever, if timeout < 0), or
> >> - an error has occured
> >> the function returns the number of bytes read or -1 in case of an error.
> >>
> >> This differs from the normal BSD-read, which blocks until *some* data is
> >> available
> >> and return that data (but nor more than size bytes).
> >>
> >> We found that more convenient to implement synchronous message-oriented
> >> applications
> >> and 'normal' Stream communication with a single and straight-forward API.
> >
> >
> >Thanks for this feedback! You may have seen the mail
> >exchange to that topic. If you are interested, could you
> >give us your feedback to the proposal written down at:
> >
> > http://wiki.cct.lsu.edu/saga/space/SAGA+API/Messages
> >
> >Best regards,
> >
> > Andre.
> >
> >
> >
> >>Best regards,
> >>Thomas
> >>
> >>
> >>Andrei Hutanu wrote:
> >>
> >>>Hi all,
> >>>
> >>>Here is my feedback regarding the Viz-LSU use case. In some cases
> >>>these requirements might be outside the scope of SAGA, I would like to
> >>>know if that is the case though ..
> >>>
> >>>*Block-based data transmission is not covered by the current API
> >>>*Resource discovery is not covered by the current API
> >>>*Job submission to multiple resources (co-scheduling) is not covered by
> >>>the current API
> >>>*Simple job submission seems to be covered by the API. Here is a list of
> >>>things
> >>>that are not covered (because outside the 80-20 rule?) and
> >>>there doesn't seem to be a "generic" attribute in the JobDefinition
> >>>class where these attributes
> >>>could be specified if the underlying scheduler happens to support them.
> >>>** Logical file requirement (the jobs needs to run on a machine where an
> >>>instance of this particular logical file exists)
> >>>** Graphics requirements
> >>>** Networking requirements (network interface, bandwidth to ..)
> >>>** Performance-based descriptions : GFlops, memory bandwidth ..
> >>>
> >>>Andrei
> >>>
> >>>Thilo Kielmann wrote:
> >>>
> >>>
> >>>>Dear all,
> >>>>
> >>>>the SAGA-RG has its use case document up for public comment, ending
> >>>>oct 30.
> >>>>
> >>>>So far, there are 0 comments! :-(
> >>>>
> >>>>I hereby urge everybody to have a look and comment, even if the
> >>>>comment is just
> >>>>trivially in favour...
> >>>>
> >>>>
> >>>>Thanks for your help,
> >>>>
> >>>>
> >>>>Thilo
> >>>>
> >>
> >>------------------------------------------------------------
> >>Dr. Thomas Eickermann
> >>Zentralinstitut fuer Angewandte Mathematik
> >>Forschungszentrum Juelich GmbH
> >>D-52425 Juelich
> >> Phone: +49 2461 61-6596
> >>Email: Th.Eickermann at fz-juelich.de Fax: +49 2461 61-6656
> >>
>
> ------------------------------------------------------------
> Dr. Thomas Eickermann
> Zentralinstitut fuer Angewandte Mathematik
> Forschungszentrum Juelich GmbH
> D-52425 Juelich
> Phone: +49 2461 61-6596
> Email: Th.Eickermann at fz-juelich.de Fax: +49 2461 61-6656
>
--
+-----------------------------------------------------------------+
| Andre Merzky | phon: +31 - 20 - 598 - 7759 |
| Vrije Universiteit Amsterdam (VU) | fax : +31 - 20 - 598 - 7653 |
| Dept. of Computer Science | mail: merzky at cs.vu.nl |
| De Boelelaan 1083a | www: http://www.merzky.net |
| 1081 HV Amsterdam, Netherlands | |
+-----------------------------------------------------------------+
More information about the saga-rg
mailing list