[ecspy] r124 committed - Added MultiprocessingMigrator to provide a way to migrate individuals ...

[ec...@googlecode.com]

Revision: 124
Author: aaron.lee.garrett
Date: Sun Jan 8 22:24:35 2012
Log: Added MultiprocessingMigrator to provide a way to migrate
individuals from one process to another on the same machine. This is useful
for certain island model ECs. This operator has been tested, but not to the
level of the others in the library. However, the migrators have yet to be
used, so adding an operator, even in a beta version, might stimulate
interest and effort here.
http://code.google.com/p/ecspy/source/detail?r=124

Modified:
/trunk/ecspy/migrators.py

=======================================
--- /trunk/ecspy/migrators.py Thu Dec 10 19:12:27 2009
+++ /trunk/ecspy/migrators.py Sun Jan 8 22:24:35 2012
@@ -25,6 +25,9 @@
along with this program. If not, see
<http://www.gnu.org/licenses/>.
"""

+import multiprocessing
+import Queue
+

def default_migration(random, population, args):
"""Do nothing.
@@ -33,3 +36,59 @@

"""
return population
+
+
+class MultiprocessingMigrator(object):
+ """Migrate among processes on the same machine.
+
+ This callable class allows individuals to migrate from one process
+ to another on the same machine. It maintains a queue of migrants
+ whose maximum length can be fixed via the ``max_migrants``
+ parameter in the constructor. If the number of migrants in the queue
+ reaches this value, new migrants are not added until earlier ones
+ are consumed. The unreliability of a multiprocessing environment
+ makes it difficult to provide guarantees. However, migrants are
+ theoretically added and consumed at the same rate, so this value
+ should determine the "freshness" of individuals, where smaller
+ queue sizes provide more recency.
+
+ An optional keyword argument in ``args`` requires the migrant to be
+ evaluated by the current EC before being inserted into the population.
+ This can be important when different populations use different
+ evaluation functions and you need to be able to compare "apples with
+ apples".
+
+ Optional keyword arguments in args:
+
+ - *evaluate_migrant* -- should new migrants be evaluated before
+ adding them to the population (default: False)
+
+ """
+ def __init__(self, max_migrants=1):
+ self.max_migrants = max_migrants
+ self.migrants = multiprocessing.Queue(self.max_migrants)
+ self.lock = multiprocessing.Lock()
+ self.__name__ = self.__class__.__name__
+
+ def __call__(self, random, population, args):
+ with self.lock:
+ evaluate_migrant = args.setdefault('evaluate_migrant', False)
+ migrant_index = random.randint(0, len(population) - 1)
+ old_migrant = population[migrant_index]
+ try:
+ migrant = self.migrants.get(block=False)
+ if evaluate_migrant:
+ fit = args["_ec"].evaluator([migrant.candidate], args)
+ migrant.fitness = fit[0]
+ args["_ec"].num_evaluations += 1
+ population[migrant_index] = migrant
+ except Queue.Empty:
+ pass
+ try:
+ self.migrants.put(old_migrant, block=False)
+ except Queue.Full:
+ pass
+ return population
+
+
+