[saga-rg] monitoring, again...

7 Nov 2005

      Hi, 

as has been discussed recently, we want to have a simple way
to add callbacks to SAGA.  The main use case for this would
be for notification on status changes for tasks and jobs.

Attached is the re-surrected monitoring package as a
proposal to achieve this.  Please note that the package
mentiones steering at various places (mostly commented out)
- that is as of yet not part of the proposal, but should
seen as a possible path for future extension to steering.

For simplicity, a code example is included.  More feedback
to the topic is welcome.  I Cc to the GridRPC folx, as they
are probably interested in that.  

Note that the example monitors not the task status, but some
other metric provided by that implementation (bytes written).

Cheers, Andre.

+-------------------------------------------------------------+
Examples:

  monitoring example: monitor a write task 
  ----------------------------------------
  short version:
  --------------

    class write_metric_cb : public saga::metric::callback
    {
     public:
       void callback (saga::metric & m)
       {
         std::cout << atoi ( m.get_attribute ("value") ) << " ";
       }
    };

    int main (int argc, char** argv)
    {
      ssize_t     len = 0;
      std::string str ("Hello SAGA\n");
      std::string url (argv[1]);

      saga::file   f (url);
      saga::task   t = f.task.write (str, &len);
      saga::metric m = t.get_metric ("Written");

      write_metric_cb cb;
      m.add_callback (cb);

      t.wait ();
    }

  monitoring example: monitor a write task
  ----------------------------------------
  long annotated version:
  -----------------------

    // this example shows how monitoring a task can be
    // implemented
    class write_metric_cb : public saga::metric::callback
    {
     private:
       saga::task t;

     public:
       write_metric_cb (const saga::task & _t) { t = _t; }

       void callback   (saga::metric & m)
       {
         int len = atoi ( m.get_attribute ("value") );
         std::cout << "bytes written: " << len             << std::endl;
         std::cout << "task status:   " << t.get_status () << std::endl;
       }
    };

    int main (int argc, char** argv)
    {
      ssize_t     len = 0;
      std::string str ("Hello SAGA\n");
      std::string url (argv[1]);

      saga::file   f (url);
      saga::task   t = f.task.write (str, &len);
      saga::metric m = t.get_metric ("Written");

      // assume that this m is a discreet metric indicating 
      // the number of bytes already written.  In general, 
      // the list of metric names has to be searched for an 
      // interesting metric if name is not known.

      // add the callback
      write_metric_cb cb;
      m.add_callback (cb);

      // wait until task is done, and give cb chance to get
      // called a couple of times
      t.wait ();
    }
+-------------------------------------------------------------+

-- 
+-----------------------------------------------------------------+
| Andre Merzky                      | phon: +31 - 20 - 598 - 7759 |
| Vrije Universiteit Amsterdam (VU) | fax : +31 - 20 - 598 - 7653 |
| Dept. of Computer Science         | mail: merzky@cs.vu.nl       |
| De Boelelaan 1083a                | www:  http://www.merzky.net |
| 1081 HV Amsterdam, Netherlands    |                             |
+-----------------------------------------------------------------+