140 lines
4.8 KiB
Python
140 lines
4.8 KiB
Python
# -*- 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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