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-rw-r--r--mail/src/leap/mail/messageflow.py149
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diff --git a/mail/src/leap/mail/messageflow.py b/mail/src/leap/mail/messageflow.py
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+# -*- coding: utf-8 -*-
+# messageflow.py
+# Copyright (C) 2013 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+"""
+Message Producers and Consumers for flow control.
+"""
+import Queue
+
+from twisted.internet.task import LoopingCall
+
+from zope.interface import Interface, implements
+
+
+class IMessageConsumer(Interface):
+
+ def consume(self, item):
+ """
+ Consumes the passed item.
+
+ :param item: an object to be consumed.
+ :type item: object
+ """
+ # TODO we could add an optional type to be passed
+ # for doing type check.
+
+ # TODO in case of errors, we could return the object to
+ # the queue, maybe wrapped in an object with a retries attribute.
+
+
+class DummyMsgConsumer(object):
+
+ implements(IMessageConsumer)
+
+ def consume(self, item):
+ """
+ Just prints the passed item.
+ """
+ print "got item %s" % item
+
+
+class MessageProducer(object):
+ """
+ A Producer class that we can use to temporarily buffer the production
+ of messages so that different objects can consume them.
+
+ This is useful for serializing the consumption of the messages stream
+ in the case of an slow resource (db), or for returning early from a
+ deferred chain and leave further processing detached from the calling loop,
+ as in the case of smtp.
+ """
+ # TODO this can be seen as a first step towards properly implementing
+ # components that implement IPushProducer / IConsumer interfaces.
+ # However, I need to think more about how to pause the streaming.
+ # In any case, the differential rate between message production
+ # and consumption is not likely (?) to consume huge amounts of memory in
+ # our current settings, so the need to pause the stream is not urgent now.
+
+ def __init__(self, consumer, queue=Queue.Queue, period=1):
+ """
+ Initializes the MessageProducer
+
+ :param consumer: an instance of a IMessageConsumer that will consume
+ the new messages.
+ :param queue: any queue implementation to be used as the temporary
+ buffer for new items. Default is a FIFO Queue.
+ :param period: the period to check for new items, in seconds.
+ """
+ # XXX should assert it implements IConsumer / IMailConsumer
+ # it should implement a `consume` method
+ self._consumer = consumer
+
+ self._queue = queue()
+ self._period = period
+
+ self._loop = LoopingCall(self._check_for_new)
+
+ # private methods
+
+ def _check_for_new(self):
+ """
+ Checks for new items in the internal queue, and calls the consume
+ method in the consumer.
+
+ If the queue is found empty, the loop is stopped. It will be started
+ again after the addition of new items.
+ """
+ # XXX right now I'm assuming that the period is good enough to allow
+ # a right pace of processing. but we could also pass the queue object
+ # to the consumer and let it choose whether process a new item or not.
+
+ if self._queue.empty():
+ self.stop()
+ else:
+ self._consumer.consume(self._queue.get())
+
+ # public methods
+
+ def put(self, item):
+ """
+ Puts a new item in the queue.
+
+ If the queue was empty, we will start the loop again.
+ """
+ was_empty = self._queue.empty()
+
+ # XXX this might raise if the queue does not accept any new
+ # items. what to do then?
+ self._queue.put(item)
+ if was_empty:
+ self.start()
+
+ def start(self):
+ """
+ Starts polling for new items.
+ """
+ if not self._loop.running:
+ self._loop.start(self._period)
+
+ def stop(self):
+ """
+ Stop polling for new items.
+ """
+ if self._loop.running:
+ self._loop.stop()
+
+
+if __name__ == "__main__":
+ from twisted.internet import reactor
+ producer = MessageProducer(DummyMsgConsumer())
+ producer.start()
+
+ for delay, item in ((2, 1), (3, 2), (4, 3),
+ (6, 4), (7, 5), (8, 6), (8.2, 7),
+ (15, 'a'), (16, 'b'), (17, 'c')):
+ reactor.callLater(delay, producer.put, item)
+ reactor.run()