executing multiple functions in background simultaneously

[Cameron Simpson]

On 14Jan2009 17:11, Catherine Moroney <Catherine.M.Moroney at jpl.nasa.gov> wrote:
> Cameron Simpson wrote:
>> On 14Jan2009 15:50, Catherine Moroney <Catherine.M.Moroney at jpl.nasa.gov> wrote:
>>> James Mills wrote:
>>>> On Wed, Jan 14, 2009 at 11:02 AM, Catherine Moroney
>>>> <Catherine.M.Moroney at jpl.nasa.gov> wrote:
>>>>> I would like to spawn off multiple instances of a function
>>>>> and run them simultaneously and then wait until they all complete.
>> [...]
>>>> Try using the python standard threading module.
>>>> Create multiple instances of Thread with target=your_function
>>>> Maintain a list of these new Thread instnaces
>>>> Join (wait) on them.
>>> What is the proper syntax to use if I wish to return variables
>>> from a function run as a thread?
>>
>> The easy thing is to use a Queue object. The background thread uses
>> .put() to place a computed result on the QUeue and the caller uses
>> .get() to read from the queue. There's an assortment of other ways too.
>>
>> Cheers,
>
> Thank you for this hint.  This goes a long way to solving
> my problem.
>
> One question - is there any way to name the objects that get
> put on a queue?  For my application, it's important to know
> which thread put a particular item on the queue.

Give each thread an id (eg give it a name when you create it, and keep
track). Instead of going:

  queue.put(value)

go:

  queue.put((threadname,value))

and at the main program:

  threadname, value = queue.get()

You're still put()ing a single value, it just happens to be a tuple
of (threadname, value).

You don't even need to use a name (and thus need to backtrack through
some name->object dictionary). If every thread has some object for its
state you can use the object instead of the threadname. Then you've got
direct access to the thread object.

Cheers,
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/