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

Add decent impl of a FileConsumer

synapse/util/file_consumer.py

@@ -0,0 +1,139 @@
+# -*- 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()

tests/util/test_file_consumer.py

@@ -0,0 +1,176 @@
+# -*- 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