[IPython-dev] finding the number of available engines

[Brian Granger]

Satra,

> i've run into a related problem. i'm trying to run code on an engine that
> can itself spawn new tasks, but i can't seem to execute function below on an
> engine. it just doesn't return if you call this through the taskclient in
> blocking mode.

This usage case of recursive tasks, is not supported with the current
twisted based code.  The reason has to do with subtle issues about how
the Twisted event loop is run in the engines versus the client.  For
the client, we run the Twisted event loop in a thread, which is not
compatible with the engine, which runs it in the main thread.  This is
probably why Min is seeing the odd GIL/thread related crash.

> it seems to block in the request for the task client and multiengine client.

Yes, this is what you would observe in the current twisted version of
the code.  The new zeromq stuff Min has written doesn't have this
limitation.

Sorry about the hassle.

Cheers,

Brian

> cheers,
>
> satra
>
> -----
> def get_ipy_clients():
>     """Get ipython clients
>
>     Returns client, taskclient and multiengineclient
>     """
>     ipyclient = None
>     taskclient = None
>     mecclient = None
>     try:
>         name = 'IPython.kernel.client'
>         __import__(name)
>         ipyclient = sys.modules[name]
>     except ImportError:
>         warn("Ipython kernel not found.  Parallel execution will be" \
>                  "unavailable", ImportWarning)
>     if ipyclient:
>         try:
>             taskclient = ipyclient.TaskClient()
>             mecclient = ipyclient.MultiEngineClient()
>         except Exception, e:
>             if isinstance(e, ConnectionRefusedError):
>                 warn("No clients found, running serially for now.")
>             if isinstance(e, ValueError):
>                 warn("Ipython kernel not installed")
>     return ipyclient, taskclient, mecclient
> ------
>
>
>
> On Wed, Jan 19, 2011 at 2:42 PM, MinRK <benjaminrk at gmail.com> wrote:
>>
>> mec.queue_status() returns a list of the form:
>> [
>>   (0, { 'pending' : "execute('a=5')", 'queue' : [ job1,job2,...] } ,
>>   (1, {'pending' : 'None', 'queue' : [] },
>>   ...
>> ]
>>
>> In this case, engine 1 is idle.  I don't know why 1's pending is 'None'
>> instead of None, that seems to be a bug.
>> So you can see the idle engines with something like:
>> def idle_engines(mec):
>>     """return list of engine_ids corresponding to idle engines."""
>>     qs = mec.queue_status()
>>     engines = []
>>     for e_id, status in qs:
>>         if status['queue']:
>>             continue
>>         if not status['pending'] or status['pending'] == 'None':
>>             engines.append(e_id)
>>     return engines
>> Which would return a list of engine_ids that are idle, the length of which
>> would of course be the number of idle engines.
>> -MinRK
>>
>>
>> On Wed, Jan 19, 2011 at 10:39, Satrajit Ghosh <satra at mit.edu> wrote:
>>>
>>> hi brian and min,
>>>
>>> i would like to do something like this:
>>>
>>> if num_engines_available() > 2:
>>>     do_x
>>> else:
>>>     do_y
>>>
>>> in 0.10.1 series is there an easy way to query how many idle engines are
>>> available?
>>>
>>> cheers,
>>>
>>> satra
>>>
>>>
>>> _______________________________________________
>>> IPython-dev mailing list
>>> IPython-dev at scipy.org
>>> http://mail.scipy.org/mailman/listinfo/ipython-dev
>>>
>>
>
>
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>



-- 
Brian E. Granger, Ph.D.
Assistant Professor of Physics
Cal Poly State University, San Luis Obispo
bgranger at calpoly.edu
ellisonbg at gmail.com