[saga-rg] task model - clearification needed

[Andre Merzky]

Hi List, 

the current task model is somewhat silent about the
mechanism for returning values from tasks.  E.g.:

  Directory            dir ("/tmp/");
  DirectoryTaskFactory dtf = dir.createTaskFactory ();
  Task                 tsk = dtf.list ("data.dat", result);

  tsk.run  ();
  tsk.wait ();

We do not specify when 'result' will be available.  I think
it is obvious that 'result' is unspecified until wait
returns indicating that the task is finished.  From that on,
result can be expected to be filled with the appropriate
data.

Another point remains open: the synchroneous list () might
throw an exception (e.g. NoSuchFile).  For the task version,
it remains curently unspecified when that exception can be
expected.  

It seems clear that allowing the implementation to throw the
exception anytime between dtf.list and tsk.wait doe not make
sense - it may then get raised in totally unrelated areas of
application code, and may easily escape catching.

I think the most sensible way is to require any excpetions
to be raised on the task finishing call, that is wait() or
cancel ().  That implies that a saga implementation has to
store any exception occuring earlier until these calls are
used.

Any comments?

Best regards, 

  Andre.


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