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# Copyright 2015 gRPC authors.
#
# 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.
"""Helpful utilities related to the stream module."""
import logging
import threading
from grpc.framework.foundation import stream
_NO_VALUE = object()
_LOGGER = logging.getLogger(__name__)
_LOGGER.addHandler(logging.NullHandler())
class TransformingConsumer(stream.Consumer):
"""A stream.Consumer that passes a transformation of its input to another."""
def __init__(self, transformation, downstream):
self._transformation = transformation
self._downstream = downstream
def consume(self, value):
self._downstream.consume(self._transformation(value))
def terminate(self):
self._downstream.terminate()
def consume_and_terminate(self, value):
self._downstream.consume_and_terminate(self._transformation(value))
class IterableConsumer(stream.Consumer):
"""A Consumer that when iterated over emits the values it has consumed."""
def __init__(self):
self._condition = threading.Condition()
self._values = []
self._active = True
def consume(self, value):
with self._condition:
if self._active:
self._values.append(value)
self._condition.notify()
def terminate(self):
with self._condition:
self._active = False
self._condition.notify()
def consume_and_terminate(self, value):
with self._condition:
if self._active:
self._values.append(value)
self._active = False
self._condition.notify()
def __iter__(self):
return self
def __next__(self):
return self.next()
def next(self):
with self._condition:
while self._active and not self._values:
self._condition.wait()
if self._values:
return self._values.pop(0)
else:
raise StopIteration()
class ThreadSwitchingConsumer(stream.Consumer):
"""A Consumer decorator that affords serialization and asynchrony."""
def __init__(self, sink, pool):
self._lock = threading.Lock()
self._sink = sink
self._pool = pool
# True if self._spin has been submitted to the pool to be called once and
# that call has not yet returned, False otherwise.
self._spinning = False
self._values = []
self._active = True
def _spin(self, sink, value, terminate):
while True:
try:
if value is _NO_VALUE:
sink.terminate()
elif terminate:
sink.consume_and_terminate(value)
else:
sink.consume(value)
except Exception as e: # pylint:disable=broad-except
_LOGGER.exception(e)
with self._lock:
if terminate:
self._spinning = False
return
elif self._values:
value = self._values.pop(0)
terminate = not self._values and not self._active
elif not self._active:
value = _NO_VALUE
terminate = True
else:
self._spinning = False
return
def consume(self, value):
with self._lock:
if self._active:
if self._spinning:
self._values.append(value)
else:
self._pool.submit(self._spin, self._sink, value, False)
self._spinning = True
def terminate(self):
with self._lock:
if self._active:
self._active = False
if not self._spinning:
self._pool.submit(self._spin, self._sink, _NO_VALUE, True)
self._spinning = True
def consume_and_terminate(self, value):
with self._lock:
if self._active:
self._active = False
if self._spinning:
self._values.append(value)
else:
self._pool.submit(self._spin, self._sink, value, True)
self._spinning = True
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