Converting existing module/objects to threads

jdlists at gmail.com jdlists at gmail.com
Thu Oct 19 05:12:30 CEST 2006


martdi wrote:
> jdlists at gmail.com wrote:
> > I have inheirted some existing code, that i will explain in a moment,
> > have needed to extend and ultimately should be able to run in threads.
> > I've done a bunch of work with python but very little with threads and
> > am looking for some pointers on how to implement, and if the lower
> > level modules/objects need to be rewritten to use threading.local for
> > all local variables.
> >
> > I have a module that communicates with a hardware device, which reads
> > data off of sensors, that can only talk with one controller at a time.
> > The controller (my module) needs to (in its simplest form) init,
> > configure the device, request data, and write out xml, sleep, repeat.
> >
> > The new request is that the device needs to be queried until a
> > condition is true, and then start requesting data.  So an instance of a
> > controller needs to be deadicated to a hardware device forever, or
> > until the program ends....which ever comes first.
> >
> > This currently works in a non-threaded version, but only for one device
> > at a time, there is a need to create a single windows(yeach) service
> > that talks to many of these devices at once.  I don't need worker
> > threads that handle seperate portions of the entire job, i need a
> > single application to spawn multiple processes to run through the
> > entire communication from configure to report, sleep until the next
> > interval time and run again.  The communication could last from 1
> > minute to 10 minutes before it ends.
> >
> >
> >   Here is the code layout in pseudocode.
> >
> > module.Object - controller.Main - handles all socket communications
> >
> > class subcontroller(controller.Main):
> >   def __init__(self,id,configurationFile):
> >    controller.Main.__init__(self)
> >    // instantiate variables and local objects that handle
> > configuration, logic and data output
> >
> >   def configure(self,configurationFile):
> >     //read configurationFile and configure device
> >
> >   def process(self):
> >     while 1:
> >       //based on configuration file, query the device until condition
> > is true and then write xml, sleep until time to repeat and run again.
> >
> > within controller there are 5 objects and subcontroller is a sinlge
> > object that loads other objects from the inherited controller.System
> >
> > I'm trying to figure out how difficult it is going to be to convert
> > this to a threaded application.  The original controller.Main is built
> > to talk to devices in series, never in parallel. so no objects are
> > considered to be thread safe, but no instance of any of the objects
> > should need to share resources with any other instance of teh same
> > object.  they would all have unique configuration files and talk to
> > devices on unique ip/ports.
> >
> > on a unix system, forking,while potentially not optimal, would be a
> > fine solution, unfortunantely this needs to run on windows.
> >
> > I know i have left out many details, but hopefully this is enough to at
> > least enable some kind soles to lend an opinnion or two.
> >
> > many thanks
> > jd
>
> Taking a look at asyncore could be worthwhile, but if you want to
> implement it with threads, you may be able to do it this way:
>
> In your main file, from where you start the program, let's call it
> main:
>
> main(self)
> Load Required configuration
> spawn threads (1 for each controller)
> define a queue object from module queue.queue used for communication
> with threads
> enter an infinite loop that checks for the conditions
>     once conditions are met, notify the proper thread
>
>
> class ControllerThread(threading.Thread):
>     def __init__(self):
>         define a queue here, to process messages from the main
>         call threading.Thread.__init__(self)
>
>     define method to load config for thread objects
>     (you might want to pass an argument to init to load your configs
> from a file)
>     (you might also want to pass the queue of the main program to the
> thread to send it messages)
>     define methods to post messages to the queue like read, send to the
> machine, stop, ...
>
>     define the run method that is what will be called when you start
> your thread.
>         this method should enter an infinite loop that will check if
> something has to be done (check in the queue).
>
>
>
>
>
> hope this might help you
> good luck

thanks for the comments.  the ControllerThread already extends a class.
 does this cause problems with classes that must extent
threading.Thread.  Normally it should not matter, but with threads i'm
unsure.  Should i just instantiate the object that i'm normally
extending in the ControllerThread.__init__, and call it from the
self.classthatusedtoextend.method(), or does it not matter.

again, thanks.




More information about the Python-list mailing list