src/python/grpcio/grpc/framework/foundation/stream_util.py

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"""Helpful utilities related to the stream module."""

import logging
import threading

from grpc.framework.foundation import stream

_NO_VALUE = object()


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, stock_reply):
    with self._condition:
      if self._active:
        self._values.append(stock_reply)
        self._condition.notify()

  def terminate(self):
    with self._condition:
      self._active = False
      self._condition.notify()

  def consume_and_terminate(self, stock_reply):
    with self._condition:
      if self._active:
        self._values.append(stock_reply)
        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
        logging.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