examples/python/cancellation/server.py

# Copyright 2019 the 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.
"""An example of cancelling requests in gRPC."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from concurrent import futures
import argparse
import contextlib
import logging
import time
import threading

import grpc
import search

from examples.python.cancellation import hash_name_pb2
from examples.python.cancellation import hash_name_pb2_grpc

_LOGGER = logging.getLogger(__name__)
_SERVER_HOST = 'localhost'
_ONE_DAY_IN_SECONDS = 60 * 60 * 24

_DESCRIPTION = "A server for finding hashes similar to names."


class HashFinder(hash_name_pb2_grpc.HashFinderServicer):

    def __init__(self, maximum_hashes):
        super(HashFinder, self).__init__()
        self._maximum_hashes = maximum_hashes

    def Find(self, request, context):
        stop_event = threading.Event()

        def on_rpc_done():
            _LOGGER.debug("Attempting to regain servicer thread.")
            stop_event.set()

        context.add_callback(on_rpc_done)
        candidates = []
        try:
            candidates = list(
                search.search(request.desired_name,
                              request.ideal_hamming_distance, stop_event,
                              self._maximum_hashes))
        except search.ResourceLimitExceededError:
            _LOGGER.info("Cancelling RPC due to exhausted resources.")
            context.cancel()
        _LOGGER.debug("Servicer thread returning.")
        if not candidates:
            return hash_name_pb2.HashNameResponse()
        return candidates[-1]

    def FindRange(self, request, context):
        stop_event = threading.Event()

        def on_rpc_done():
            _LOGGER.debug("Attempting to regain servicer thread.")
            stop_event.set()

        context.add_callback(on_rpc_done)
        secret_generator = search.search(
            request.desired_name,
            request.ideal_hamming_distance,
            stop_event,
            self._maximum_hashes,
            interesting_hamming_distance=request.interesting_hamming_distance)
        try:
            for candidate in secret_generator:
                yield candidate
        except search.ResourceLimitExceededError:
            _LOGGER.info("Cancelling RPC due to exhausted resources.")
            context.cancel()
        _LOGGER.debug("Regained servicer thread.")


@contextlib.contextmanager
def _running_server(port, maximum_hashes):
    # We use only a single servicer thread here to demonstrate that, if managed
    # carefully, cancelled RPCs can need not continue occupying servicers
    # threads.
    server = grpc.server(
        futures.ThreadPoolExecutor(max_workers=1), maximum_concurrent_rpcs=1)
    hash_name_pb2_grpc.add_HashFinderServicer_to_server(
        HashFinder(maximum_hashes), server)
    address = '{}:{}'.format(_SERVER_HOST, port)
    actual_port = server.add_insecure_port(address)
    server.start()
    print("Server listening at '{}'".format(address))
    try:
        yield actual_port
    except KeyboardInterrupt:
        pass
    finally:
        server.stop(None)


def main():
    parser = argparse.ArgumentParser(description=_DESCRIPTION)
    parser.add_argument(
        '--port',
        type=int,
        default=50051,
        nargs='?',
        help='The port on which the server will listen.')
    parser.add_argument(
        '--maximum-hashes',
        type=int,
        default=1000000,
        nargs='?',
        help='The maximum number of hashes to search before cancelling.')
    args = parser.parse_args()
    with _running_server(args.port, args.maximum_hashes):
        while True:
            time.sleep(_ONE_DAY_IN_SECONDS)


if __name__ == "__main__":
    logging.basicConfig()
    main()