select.py

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#!/usr/bin/env python
#
# Copyright 2012 Facebook
#
# 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.
"""Select-based IOLoop implementation.

Used as a fallback for systems that don't support epoll or kqueue.
"""
from __future__ import absolute_import, division, print_function, with_statement

import select

from tornado.ioloop import IOLoop, PollIOLoop


class _Select(object):
    """A simple, select()-based IOLoop implementation for non-Linux systems"""
    def __init__(self):
        self.read_fds = set()
        self.write_fds = set()
        self.error_fds = set()
        self.fd_sets = (self.read_fds, self.write_fds, self.error_fds)

    def close(self):
        pass

    def register(self, fd, events):
        if fd in self.read_fds or fd in self.write_fds or fd in self.error_fds:
            raise IOError("fd %s already registered" % fd)
        if events & IOLoop.READ:
            self.read_fds.add(fd)
        if events & IOLoop.WRITE:
            self.write_fds.add(fd)
        if events & IOLoop.ERROR:
            self.error_fds.add(fd)
            # Closed connections are reported as errors by epoll and kqueue,
            # but as zero-byte reads by select, so when errors are requested
            # we need to listen for both read and error.
            self.read_fds.add(fd)

    def modify(self, fd, events):
        self.unregister(fd)
        self.register(fd, events)

    def unregister(self, fd):
        self.read_fds.discard(fd)
        self.write_fds.discard(fd)
        self.error_fds.discard(fd)

    def poll(self, timeout):
        readable, writeable, errors = select.select(
            self.read_fds, self.write_fds, self.error_fds, timeout)
        events = {}
        for fd in readable:
            events[fd] = events.get(fd, 0) | IOLoop.READ
        for fd in writeable:
            events[fd] = events.get(fd, 0) | IOLoop.WRITE
        for fd in errors:
            events[fd] = events.get(fd, 0) | IOLoop.ERROR
        return events.items()


class SelectIOLoop(PollIOLoop):
    def initialize(self, **kwargs):
        super(SelectIOLoop, self).initialize(impl=_Select(), **kwargs)