:-D Thanks, Andre. Quoting [Thomas Eickermann] (Dec 13 2005):
Hi Andre,
sorry for responding so slowly, but times are tough as usual in December ...
I finally surrender to your arguments. I was not aware that SAGA will provide callbacks (via the Monitoring interface ?). Using such callbacks, you can probably solve the problem that i have raised in most cases. The rest would fall under the 80/20 rule.
Thanks for the discussion, Thomas
Andre Merzky wrote:
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@fz-juelich.de Fax: +49 2461 61-6656
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