Merge pull request #2804 from matrix-org/erikj/file_consumer
Add decent impl of a FileConsumer
This commit is contained in:
Erik Johnston
GitHub
commit
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# -*- coding: utf-8 -*-
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# Copyright 2018 New Vector Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from twisted.internet import threads, reactor
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from synapse.util.logcontext import make_deferred_yieldable, preserve_fn
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import Queue
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class BackgroundFileConsumer(object):
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"""A consumer that writes to a file like object. Supports both push
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and pull producers
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Args:
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file_obj (file): The file like object to write to. Closed when
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finished.
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"""
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# For PushProducers pause if we have this many unwritten slices
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_PAUSE_ON_QUEUE_SIZE = 5
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# And resume once the size of the queue is less than this
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_RESUME_ON_QUEUE_SIZE = 2
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def __init__(self, file_obj):
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self._file_obj = file_obj
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# Producer we're registered with
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self._producer = None
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# True if PushProducer, false if PullProducer
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self.streaming = False
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# For PushProducers, indicates whether we've paused the producer and
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# need to call resumeProducing before we get more data.
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self._paused_producer = False
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# Queue of slices of bytes to be written. When producer calls
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# unregister a final None is sent.
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self._bytes_queue = Queue.Queue()
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# Deferred that is resolved when finished writing
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self._finished_deferred = None
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# If the _writer thread throws an exception it gets stored here.
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self._write_exception = None
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def registerProducer(self, producer, streaming):
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"""Part of IConsumer interface
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Args:
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producer (IProducer)
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streaming (bool): True if push based producer, False if pull
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based.
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"""
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if self._producer:
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raise Exception("registerProducer called twice")
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self._producer = producer
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self.streaming = streaming
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self._finished_deferred = preserve_fn(threads.deferToThread)(self._writer)
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if not streaming:
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self._producer.resumeProducing()
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def unregisterProducer(self):
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"""Part of IProducer interface
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"""
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self._producer = None
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if not self._finished_deferred.called:
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self._bytes_queue.put_nowait(None)
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def write(self, bytes):
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"""Part of IProducer interface
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"""
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if self._write_exception:
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raise self._write_exception
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if self._finished_deferred.called:
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raise Exception("consumer has closed")
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self._bytes_queue.put_nowait(bytes)
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# If this is a PushProducer and the queue is getting behind
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# then we pause the producer.
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if self.streaming and self._bytes_queue.qsize() >= self._PAUSE_ON_QUEUE_SIZE:
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self._paused_producer = True
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self._producer.pauseProducing()
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def _writer(self):
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"""This is run in a background thread to write to the file.
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"""
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try:
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while self._producer or not self._bytes_queue.empty():
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# If we've paused the producer check if we should resume the
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# producer.
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if self._producer and self._paused_producer:
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if self._bytes_queue.qsize() <= self._RESUME_ON_QUEUE_SIZE:
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reactor.callFromThread(self._resume_paused_producer)
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bytes = self._bytes_queue.get()
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# If we get a None (or empty list) then that's a signal used
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# to indicate we should check if we should stop.
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if bytes:
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self._file_obj.write(bytes)
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# If its a pull producer then we need to explicitly ask for
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# more stuff.
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if not self.streaming and self._producer:
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reactor.callFromThread(self._producer.resumeProducing)
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except Exception as e:
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self._write_exception = e
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raise
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finally:
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self._file_obj.close()
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def wait(self):
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"""Returns a deferred that resolves when finished writing to file
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"""
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return make_deferred_yieldable(self._finished_deferred)
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def _resume_paused_producer(self):
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"""Gets called if we should resume producing after being paused
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"""
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if self._paused_producer and self._producer:
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self._paused_producer = False
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self._producer.resumeProducing()
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@ -0,0 +1,176 @@
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# -*- coding: utf-8 -*-
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# Copyright 2018 New Vector Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from twisted.internet import defer, reactor
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from mock import NonCallableMock
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from synapse.util.file_consumer import BackgroundFileConsumer
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from tests import unittest
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from StringIO import StringIO
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import threading
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class FileConsumerTests(unittest.TestCase):
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@defer.inlineCallbacks
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def test_pull_consumer(self):
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string_file = StringIO()
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consumer = BackgroundFileConsumer(string_file)
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try:
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producer = DummyPullProducer()
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yield producer.register_with_consumer(consumer)
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yield producer.write_and_wait("Foo")
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self.assertEqual(string_file.getvalue(), "Foo")
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yield producer.write_and_wait("Bar")
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self.assertEqual(string_file.getvalue(), "FooBar")
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finally:
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consumer.unregisterProducer()
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yield consumer.wait()
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self.assertTrue(string_file.closed)
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@defer.inlineCallbacks
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def test_push_consumer(self):
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string_file = BlockingStringWrite()
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consumer = BackgroundFileConsumer(string_file)
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try:
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producer = NonCallableMock(spec_set=[])
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consumer.registerProducer(producer, True)
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consumer.write("Foo")
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yield string_file.wait_for_n_writes(1)
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self.assertEqual(string_file.buffer, "Foo")
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consumer.write("Bar")
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yield string_file.wait_for_n_writes(2)
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self.assertEqual(string_file.buffer, "FooBar")
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finally:
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consumer.unregisterProducer()
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yield consumer.wait()
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self.assertTrue(string_file.closed)
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@defer.inlineCallbacks
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def test_push_producer_feedback(self):
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string_file = BlockingStringWrite()
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consumer = BackgroundFileConsumer(string_file)
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try:
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producer = NonCallableMock(spec_set=["pauseProducing", "resumeProducing"])
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resume_deferred = defer.Deferred()
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producer.resumeProducing.side_effect = lambda: resume_deferred.callback(None)
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consumer.registerProducer(producer, True)
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number_writes = 0
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with string_file.write_lock:
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for _ in range(consumer._PAUSE_ON_QUEUE_SIZE):
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consumer.write("Foo")
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number_writes += 1
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producer.pauseProducing.assert_called_once()
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yield string_file.wait_for_n_writes(number_writes)
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yield resume_deferred
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producer.resumeProducing.assert_called_once()
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finally:
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consumer.unregisterProducer()
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yield consumer.wait()
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self.assertTrue(string_file.closed)
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class DummyPullProducer(object):
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def __init__(self):
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self.consumer = None
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self.deferred = defer.Deferred()
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def resumeProducing(self):
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d = self.deferred
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self.deferred = defer.Deferred()
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d.callback(None)
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def write_and_wait(self, bytes):
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d = self.deferred
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self.consumer.write(bytes)
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return d
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def register_with_consumer(self, consumer):
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d = self.deferred
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self.consumer = consumer
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self.consumer.registerProducer(self, False)
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return d
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class BlockingStringWrite(object):
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def __init__(self):
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self.buffer = ""
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self.closed = False
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self.write_lock = threading.Lock()
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self._notify_write_deferred = None
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self._number_of_writes = 0
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def write(self, bytes):
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with self.write_lock:
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self.buffer += bytes
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self._number_of_writes += 1
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reactor.callFromThread(self._notify_write)
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def close(self):
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self.closed = True
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def _notify_write(self):
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"Called by write to indicate a write happened"
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with self.write_lock:
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if not self._notify_write_deferred:
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return
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d = self._notify_write_deferred
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self._notify_write_deferred = None
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d.callback(None)
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@defer.inlineCallbacks
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def wait_for_n_writes(self, n):
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"Wait for n writes to have happened"
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while True:
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with self.write_lock:
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if n <= self._number_of_writes:
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return
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if not self._notify_write_deferred:
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self._notify_write_deferred = defer.Deferred()
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d = self._notify_write_deferred
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yield d
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