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Merge pull request #2804 from matrix-org/erikj/file_consumer 

Add decent impl of a FileConsumer
This commit is contained in:
Erik Johnston 2018-01-18 16:31:33 +00:00 committed by GitHub
parent 9a89dae8c5 be0dfcd4a2
commit b6dc7044a9
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2 changed files with 315 additions and 0 deletions
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139
synapse/util/file_consumer.py Normal file
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# -*- coding: utf-8 -*-
# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from twisted.internet import threads, reactor
from synapse.util.logcontext import make_deferred_yieldable, preserve_fn
import Queue
class BackgroundFileConsumer(object):
"""A consumer that writes to a file like object. Supports both push
and pull producers
Args:
file_obj (file): The file like object to write to. Closed when
finished.
"""
# For PushProducers pause if we have this many unwritten slices
_PAUSE_ON_QUEUE_SIZE = 5
# And resume once the size of the queue is less than this
_RESUME_ON_QUEUE_SIZE = 2
def __init__(self, file_obj):
self._file_obj = file_obj
# Producer we're registered with
self._producer = None
# True if PushProducer, false if PullProducer
self.streaming = False
# For PushProducers, indicates whether we've paused the producer and
# need to call resumeProducing before we get more data.
self._paused_producer = False
# Queue of slices of bytes to be written. When producer calls
# unregister a final None is sent.
self._bytes_queue = Queue.Queue()
# Deferred that is resolved when finished writing
self._finished_deferred = None
# If the _writer thread throws an exception it gets stored here.
self._write_exception = None
def registerProducer(self, producer, streaming):
"""Part of IConsumer interface
Args:
producer (IProducer)
streaming (bool): True if push based producer, False if pull
based.
"""
if self._producer:
raise Exception("registerProducer called twice")
self._producer = producer
self.streaming = streaming
self._finished_deferred = preserve_fn(threads.deferToThread)(self._writer)
if not streaming:
self._producer.resumeProducing()
def unregisterProducer(self):
"""Part of IProducer interface
"""
self._producer = None
if not self._finished_deferred.called:
self._bytes_queue.put_nowait(None)
def write(self, bytes):
"""Part of IProducer interface
"""
if self._write_exception:
raise self._write_exception
if self._finished_deferred.called:
raise Exception("consumer has closed")
self._bytes_queue.put_nowait(bytes)
# If this is a PushProducer and the queue is getting behind
# then we pause the producer.
if self.streaming and self._bytes_queue.qsize() >= self._PAUSE_ON_QUEUE_SIZE:
self._paused_producer = True
self._producer.pauseProducing()
def _writer(self):
"""This is run in a background thread to write to the file.
"""
try:
while self._producer or not self._bytes_queue.empty():
# If we've paused the producer check if we should resume the
# producer.
if self._producer and self._paused_producer:
if self._bytes_queue.qsize() <= self._RESUME_ON_QUEUE_SIZE:
reactor.callFromThread(self._resume_paused_producer)
bytes = self._bytes_queue.get()
# If we get a None (or empty list) then that's a signal used
# to indicate we should check if we should stop.
if bytes:
self._file_obj.write(bytes)
# If its a pull producer then we need to explicitly ask for
# more stuff.
if not self.streaming and self._producer:
reactor.callFromThread(self._producer.resumeProducing)
except Exception as e:
self._write_exception = e
raise
finally:
self._file_obj.close()
def wait(self):
"""Returns a deferred that resolves when finished writing to file
"""
return make_deferred_yieldable(self._finished_deferred)
def _resume_paused_producer(self):
"""Gets called if we should resume producing after being paused
"""
if self._paused_producer and self._producer:
self._paused_producer = False
self._producer.resumeProducing()

176
tests/util/test_file_consumer.py Normal file
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# -*- coding: utf-8 -*-
# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from twisted.internet import defer, reactor
from mock import NonCallableMock
from synapse.util.file_consumer import BackgroundFileConsumer
from tests import unittest
from StringIO import StringIO
import threading
class FileConsumerTests(unittest.TestCase):
@defer.inlineCallbacks
def test_pull_consumer(self):
string_file = StringIO()
consumer = BackgroundFileConsumer(string_file)
try:
producer = DummyPullProducer()
yield producer.register_with_consumer(consumer)
yield producer.write_and_wait("Foo")
self.assertEqual(string_file.getvalue(), "Foo")
yield producer.write_and_wait("Bar")
self.assertEqual(string_file.getvalue(), "FooBar")
finally:
consumer.unregisterProducer()
yield consumer.wait()
self.assertTrue(string_file.closed)
@defer.inlineCallbacks
def test_push_consumer(self):
string_file = BlockingStringWrite()
consumer = BackgroundFileConsumer(string_file)
try:
producer = NonCallableMock(spec_set=[])
consumer.registerProducer(producer, True)
consumer.write("Foo")
yield string_file.wait_for_n_writes(1)
self.assertEqual(string_file.buffer, "Foo")
consumer.write("Bar")
yield string_file.wait_for_n_writes(2)
self.assertEqual(string_file.buffer, "FooBar")
finally:
consumer.unregisterProducer()
yield consumer.wait()
self.assertTrue(string_file.closed)
@defer.inlineCallbacks
def test_push_producer_feedback(self):
string_file = BlockingStringWrite()
consumer = BackgroundFileConsumer(string_file)
try:
producer = NonCallableMock(spec_set=["pauseProducing", "resumeProducing"])
resume_deferred = defer.Deferred()
producer.resumeProducing.side_effect = lambda: resume_deferred.callback(None)
consumer.registerProducer(producer, True)
number_writes = 0
with string_file.write_lock:
for _ in range(consumer._PAUSE_ON_QUEUE_SIZE):
consumer.write("Foo")
number_writes += 1
producer.pauseProducing.assert_called_once()
yield string_file.wait_for_n_writes(number_writes)
yield resume_deferred
producer.resumeProducing.assert_called_once()
finally:
consumer.unregisterProducer()
yield consumer.wait()
self.assertTrue(string_file.closed)
class DummyPullProducer(object):
def __init__(self):
self.consumer = None
self.deferred = defer.Deferred()
def resumeProducing(self):
d = self.deferred
self.deferred = defer.Deferred()
d.callback(None)
def write_and_wait(self, bytes):
d = self.deferred
self.consumer.write(bytes)
return d
def register_with_consumer(self, consumer):
d = self.deferred
self.consumer = consumer
self.consumer.registerProducer(self, False)
return d
class BlockingStringWrite(object):
def __init__(self):
self.buffer = ""
self.closed = False
self.write_lock = threading.Lock()
self._notify_write_deferred = None
self._number_of_writes = 0
def write(self, bytes):
with self.write_lock:
self.buffer += bytes
self._number_of_writes += 1
reactor.callFromThread(self._notify_write)
def close(self):
self.closed = True
def _notify_write(self):
"Called by write to indicate a write happened"
with self.write_lock:
if not self._notify_write_deferred:
return
d = self._notify_write_deferred
self._notify_write_deferred = None
d.callback(None)
@defer.inlineCallbacks
def wait_for_n_writes(self, n):
"Wait for n writes to have happened"
while True:
with self.write_lock:
if n <= self._number_of_writes:
return
if not self._notify_write_deferred:
self._notify_write_deferred = defer.Deferred()
d = self._notify_write_deferred
yield d