[saga-rg] tasks and jobs...

[Andre Merzky]

Hi Graeme, 

Quoting [G.E.POUND at soton.ac.uk] (Feb 06 2006):
> 
> Andre,
> 
> I have a couple of reservations about this action that you may be able to
> answer.
> 
> I had been hoping to avoid implementing the 'Task' namespace in the java
> bindings and encourage developers to use the language's support to
> threading to allow asynchronous method calls in the client code.

I understood that much from your last comments, but my
limited knowledge does not allow me to give a qualified
answer I'm afraid.  Hmm, maybe we can work this out together
:-)

Could you post some code examples to demonstrate how a
asynchronous seek (for example) would be coded in a java
application?

The C++ code would be:

  saga::file f (url);
  saga::task t = f.seek <saga::task> (off, whence, &pos);

  t.run  ();
  t.wait ();


Next question is, how would a java application manage many
tasks - i.e. is there something similar to a
saga::task_container ?

  saga::task_container tc;

  tc.add (task_1);
  tc.add (task_2);
  tc.add (task_3);

  tc.run  ();
  tc.wait ();


> I am therefore concerned about creating a dependency between the
> 'JobManagement' namespace and the 'Task' namespace.

I think, for the java bindings that would mean that job
implements the task interface.  Apart from the run you
mention below, the semantic of the task interface is
actually included in job already, more or less, only the
methods and states are differently named  (that is one
motivation for the proposal really).


> The submission of remote jobs is naturally asynchronous, and there are
> natural semantic parallels to the asynchronous model described by the
> 'Task' namespace. However from my reading of the API I understood these two
> models to be independent in purpose; creating a dependency could hinder the
> natural description (and development) of these two areas of the API.

Both models are not really different on purpose.  Would you
see an advantage of having them truly separate?

> 
> The idea of a job container for the management of a large number of remote
> jobs is useful. However the TaskContainter does not appear to be wholly
> compatible; the run() method to start the asynchronous operations is
> unnecessary for jobs that have been submitted to a remote resource.

You are right.  Well, that might be somewhat subtle, but in
the example code below, the submit_job() call is accompanied
by c new reate_job().  That creates a job which needs to be
run(), which would make it compatiple to the task model.

  saga::job j1 = job_server.create_job (jd);
  // job state is 'pending'

  j1.run  ();
  // job state is 'running' or so - 'not pending'

  j1.wait ();
  // job state is Done or Failed

  
  
  saga::job j2 = job_server.submit_job (jd);
  // job state is 'running' or so - 'not pending'

  j1.wait ();
  // job state is Done or Failed


That is very similar to the semantics we have for tasks...


One reason for this proposal is additionally that we want to
approach the bulk operations soon.  Consider a parameter
sweep, where 100.000 jobs are to be run.

 for ( i = 0; i < 100.000; i++ )
 {
   jobs[i] = job_server.submit (jd[i]); // SUBMIT
 }
 
 for ( i = 0; i < 100.000; i++ )
 {
   jobs[i].wait ();
 }

As for each submission, you are very likely to have at least
one remote operation (they are independend), that will take
a lot of time.

Compare that to:

 task_container tc;

 for ( i = 0; i < 100.000; i++ )
 {
   tc.add (job_server.create (jd[i])); // CREATE
 }

 tc.run  ();
 tc.wait ();

It is rather straigh forward to optimize the task container
for bulk job submission, or bulk operations in general (we
hope).


What I am not sure is, what would that look like in native
java?  Are there similar mechanisms?


Looking forward to your comments, 

  Andre.


> Graeme
> 
> 
> Quoting Andre Merzky <andre at merzky.net>:
> 
> > Hi,
> >
> > I just had a discussion with Thilo about the topic, as he
> > and me obviously talked somewhat orthogonal to each other...
> >
> > Well, now we have the same opinion, kind of, and I have
> > barely any bruises...  Anyway, I want to summarize our point
> > here, as I probably was not really clear in my initial post.
> >
> > Sorry if re-iteration of the topic bores you...
> >
> > So, we have tasks, which represent async operations, with a
> > couple of states attached, and the ability to call run(),
> > wait() and cancel() on these.  And we can collect them in
> > containers, and wait() on many of these tasks conveniently.
> >
> > And then we have jobs, which represent remote executables,
> > with a couple of states attached, and the ability to call
> > run (== create them), wait() and cancel().  And some more
> > methods.  And we can't collect them in containers right now,
> > but would like to.
> >
> > You see the similarities, right?  Its even more obvious in
> > code:
> >
> >   Tasks:
> >   --------------------------------------------
> >     task_container tc;
> >     task t = file.copy <saga::task> (...);
> >          t.run  (   );
> >          t.wait (1.0);
> >
> >         tc.add  (t);
> >         tc.wait ( );
> >   --------------------------------------------
> >
> >   Jobs:
> >   --------------------------------------------
> >     job_container jc;
> >     job j = job_server.submit (job_descr);
> >         j.wait (1.0);
> >
> >        jc.add  (j);
> >        jc.wait ( );
> >   --------------------------------------------
> >
> >   slightly changed:
> >   --------------------------------------------
> >     job_container jc;
> >   ! job j = job_server.create (job_descr);
> >   +     j.run  (   );
> >         j.wait (1.0);
> >
> >        jc.add  (j);
> >        jc.wait ( );
> >   --------------------------------------------
> >
> > The similarities are obvious I think.  Now, if job would
> > IMPLEMENT the task interface (or inherit from task), we
> > would unify both classes, and hence:
> >
> >   - simplify jobs (leave only those methods which are
> >     specific to jobs, like migrate, signal, ...
> >
> >   - allow to out jobs into task containers, efficiently
> >     handling large amounts of jobs and other tasks
> >
> >   - have the API and used paradigms more uniform.
> >
> > Also, if later tasks get suspendable, as Gregor rightly
> > suggested, we can move more methods to tasks, w/o breaking
> > the paradigms.
> >
> > In terms of state, following mappings would be appropriate:
> >
> >   job::Pending -> task::Pending
> >   job::Done    -> task::Done
> >   job::Failed  -> task::Failed
> >   job::???     -> task::Cancelled
> >
> >   job::Queued,Running,Pre/Poststaging,... -> task::Running
> >
> > So, no adjustements to the statet models are needed AFAICS,
> > apart from Cancelled
> > (Does it make sense   on jobs?
> >  Should job::stop     be job::cancel?
> >  Should tasks::cancel be task::job?)
> >
> > Hope that clearifies things.  I think Gregor was on target
> > with his remarks, and Hartmut signalled consent as well.
> > And I think I convinced Thilo (Andre rubs his bruises).
> >
> > Unless there is any opposition, I'll go ahead and document
> > that in the strawman then, ok?
> >
> > Cheers, Andre.
> >
> >
> > Quoting [Thilo Kielmann] (Feb 04 2006):
> > > Date: Sat, 4 Feb 2006 22:29:41 +0100
> > > From: Thilo Kielmann <kielmann at cs.vu.nl>
> > > To: saga-rg at ggf.org
> > > Subject: Re: [saga-rg] tasks and jobs...
> > >
> > > > Wouldn't it be useful to have jobs implementing the task
> > > > interface?
> > >
> > > Certainly, no.
> > > Jobs and Tasks are two different things, and they are this on purpose.
> > >
> > > However, Tasks always have been the mechanism for asynchronous
> > operation,
> > > which is kind-of obsoleted by having asynchronous ops directly.
> > >
> > > If you want to work on the "S" of SAGA: why not unify both Tasks and
> > Jobs
> > > into a better "Job" notion, and do local asynchronous operations via
> > > async, local calls?
> > >
> > > Thilo
> > --
> > "So much time, so little to do..."  -- Garfield
> >
> >
> >
> >
> 
> 



-- 
"So much time, so little to do..."  -- Garfield