""" @author: Christopher Arndt @version: 1.1 @see: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/435883 Easy to use object-oriented thread pool framework. A thread pool is a class that maintains a pool of worker threads to perform time consuming operations in parallel. It assigns jobs to the threads by putting them in a work request queue, where they are picked up by the next available thread. This then performs the requested operation in the background and puts the results in a another queue. The thread pool class can then collect the results from all threads from this queue as soon as they become available or after all threads have finished their work. It's also possible, to define callbacks to handle each result as it comes in. The basic concept and some code was taken from the book "Python in a Nutshell" by Alex Martelli, copyright 2003, ISBN 0-596-00188-6, from section 14.5 "Threaded Program Architecture". I wrapped the main program logic in the ThreadPool class, added the WorkRequest class and the callback system and tweaked the code here and there. Basic usage: >>> main = ThreadPool(poolsize) >>> requests = makeRequests(some_callable, list_of_args, callback) >>> [main.putRequests(req) for req in requests] >>> main.wait() See the end of the module code for a brief, annotated usage example. """ __all__ = ['makeRequests', 'NoResultsPending', 'NoWorkersAvailable', 'ThreadPool', 'WorkRequest', 'WorkerThread'] __author__ = 'Christopher Arndt' __version__ = '1.1' __date__ = '2005-07-19' import threading, Queue class NoResultsPending(Exception): """All work requests have been processed.""" pass class NoWorkersAvailable(Exception): """No worker threads available to process remaining requests.""" pass class WorkerThread(threading.Thread): """Background thread connected to the requests/results queues. A worker thread sits in the background and picks up work requests from one queue and puts the results in another until it is dismissed. """ def __init__ (self, requestsQueue, resultsQueue, **kwds): """Set up thread in damonic mode and start it immediatedly. requestsQueue and resultQueue are instances of Queue.Queue passed by the ThreadPool class when it creates a new worker thread. """ threading.Thread.__init__(self, **kwds) self.setDaemon(1) self.workRequestQueue = requestsQueue self.resultQueue = resultsQueue self._dismissed = threading.Event() self.start() def run(self): """Repeatedly process the job queue until told to exit. """ while not self._dismissed.isSet(): # thread blocks here, if queue empty request = self.workRequestQueue.get() if self._dismissed.isSet(): # return the work request we just picked up self.workRequestQueue.put(request) break # and exit # XXX catch exceptions here and stick them to request object self.resultQueue.put( (request, request.callable(*request.args, **request.kwds)) ) def dismiss(self): """Sets a flag to tell the thread to exit when done with current job. """ self._dismissed.set() class WorkRequest: """A request to execute a callable for putting in the request queue later. See the module function makeRequests() for the common case where you want to build several work requests for the same callable but different arguments for each call. """ def __init__ (self, callable, args=None, kwds=None, requestID=None, callback=None): """A work request consists of the a callable to be executed by a worker thread, a list of positional arguments, a dictionary of keyword arguments. A callback function can be specified, that is called when the results of the request are picked up from the result queue. It must accept two arguments, the request object and it's results in that order. If you want to pass additional information to the callback, just stick it on the request object. requestID, if given, must be hashable as it is used by the ThreadPool class to store the results of that work request in a dictionary. It defaults to the return value of id(self). """ if requestID is None: self.requestID = id(self) else: self.requestID = requestID self.callback = callback self.callable = callable self.args = args or [] self.kwds = kwds or {} class ThreadPool: """A thread pool, distributing work requests and collecting results. See the module doctring for more information. """ def __init__ (self, num_workers, q_size=0): """Set up the thread pool and start num_workers worker threads. num_workers is the number of worker threads to start initialy. If q_size > 0 the size of the work request is limited and the thread pool blocks when queue is full and it tries to put more work requests in it. """ self.requestsQueue = Queue.Queue(q_size) self.resultsQueue = Queue.Queue() self.workers = [] self.workRequests = {} self.createWorkers(num_workers) def createWorkers(self, num_workers): """Add num_workers worker threads to the pool.""" for i in range(num_workers): self.workers.append(WorkerThread(self.requestsQueue, self.resultsQueue)) def dismissWorkers(self, num_workers): """Tell num_workers worker threads to to quit when they're done.""" for i in range(min(num_workers, len(self.workers))): worker = self.workers.pop() worker.dismiss() def putRequest(self, request): """Put work request into work queue and save for later.""" self.requestsQueue.put(request) self.workRequests[request.requestID] = request def poll(self, block=False): """Process any new results in the queue.""" while 1: try: # still results pending? if not self.workRequests: raise NoResultsPending # are there still workers to process remaining requests? elif block and not self.workers: raise NoWorkersAvailable # get back next results request, result = self.resultsQueue.get(block=block) # and hand them to the callback, if any if request.callback: request.callback(request, result) del self.workRequests[request.requestID] except Queue.Empty: break def wait(self): """Wait for results, blocking until all have arrived.""" while 1: try: self.poll(True) except NoResultsPending: break def makeRequests(callable, args_list, callback=None): """Convenience function for building several work requests for the same callable with different arguments for each call. args_list contains the parameters for each invocation of callable. Each item in 'argslist' should be either a 2-item tuple of the list of positional arguments and a dictionary of keyword arguments or a single, non-tuple argument. callback is called when the results arrive in the result queue. """ requests = [] for item in args_list: if item is None: """no arguments""" requests.append( WorkRequest(callable, None, None, callback=callback)) elif item == isinstance(item, tuple): """arguments and keywords""" requests.append( WorkRequest(callable, item[0], item[1], callback=callback)) else: """only keywords""" requests.append( WorkRequest(callable, [item], None, callback=callback)) return requests if __name__ == '__main__': import random import time # the work the threads will have to do (rather trivial in our example) def do_something(data): time.sleep(random.randint(1,5)) return round(random.random() * data, 5) # this will be called each time a result is available def print_result(request, result): print "Result: %s from request #%s" % (result, request.requestID) # assemble the arguments for each job to a list... data = [random.randint(1,10) for i in range(20)] # ... and build a WorkRequest object for each item in data requests = makeRequests(do_something, data, print_result) # we create a pool of 10 worker threads main = ThreadPool(3) # then we put the work requests in the queue... for req in requests: main.putRequest(req) print "Work request #%s added." % req.requestID # or shorter: # [main.putRequest(req) for req in requests] # ...and wait for the results to arrive in the result queue # wait() will return when results for all work requests have arrived # main.wait() # alternatively poll for results while doing something else: i = 0 while 1: try: main.poll() print "Main thread working..." time.sleep(0.5) if i == 10: print "Adding 3 more worker threads..." main.createWorkers(3) i += 1 except (KeyboardInterrupt, NoResultsPending): break