[saga-rg] tasks and jobs...

[Andre Merzky]

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