grpc/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

import argparse
from concurrent import futures
import logging
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"

_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.")


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))
    return server


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()
    server = _running_server(args.port, args.maximum_hashes)
    server.wait_for_termination()


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