ops

lib/tornado/platform/asyncio.py

@@ -0,0 +1,299 @@
+"""Bridges between the `asyncio` module and Tornado IOLoop.
+
+.. versionadded:: 3.2
+
+This module integrates Tornado with the ``asyncio`` module introduced
+in Python 3.4. This makes it possible to combine the two libraries on
+the same event loop.
+
+.. deprecated:: 5.0
+
+   While the code in this module is still used, it is now enabled
+   automatically when `asyncio` is available, so applications should
+   no longer need to refer to this module directly.
+
+.. note::
+
+   Tornado requires the `~asyncio.AbstractEventLoop.add_reader` family of
+   methods, so it is not compatible with the `~asyncio.ProactorEventLoop` on
+   Windows. Use the `~asyncio.SelectorEventLoop` instead.
+"""
+
+from __future__ import absolute_import, division, print_function
+import functools
+
+from tornado.gen import convert_yielded
+from tornado.ioloop import IOLoop
+from tornado import stack_context
+
+import asyncio
+
+
+class BaseAsyncIOLoop(IOLoop):
+    def initialize(self, asyncio_loop, **kwargs):
+        self.asyncio_loop = asyncio_loop
+        # Maps fd to (fileobj, handler function) pair (as in IOLoop.add_handler)
+        self.handlers = {}
+        # Set of fds listening for reads/writes
+        self.readers = set()
+        self.writers = set()
+        self.closing = False
+        # If an asyncio loop was closed through an asyncio interface
+        # instead of IOLoop.close(), we'd never hear about it and may
+        # have left a dangling reference in our map. In case an
+        # application (or, more likely, a test suite) creates and
+        # destroys a lot of event loops in this way, check here to
+        # ensure that we don't have a lot of dead loops building up in
+        # the map.
+        #
+        # TODO(bdarnell): consider making self.asyncio_loop a weakref
+        # for AsyncIOMainLoop and make _ioloop_for_asyncio a
+        # WeakKeyDictionary.
+        for loop in list(IOLoop._ioloop_for_asyncio):
+            if loop.is_closed():
+                del IOLoop._ioloop_for_asyncio[loop]
+        IOLoop._ioloop_for_asyncio[asyncio_loop] = self
+        super(BaseAsyncIOLoop, self).initialize(**kwargs)
+
+    def close(self, all_fds=False):
+        self.closing = True
+        for fd in list(self.handlers):
+            fileobj, handler_func = self.handlers[fd]
+            self.remove_handler(fd)
+            if all_fds:
+                self.close_fd(fileobj)
+        # Remove the mapping before closing the asyncio loop. If this
+        # happened in the other order, we could race against another
+        # initialize() call which would see the closed asyncio loop,
+        # assume it was closed from the asyncio side, and do this
+        # cleanup for us, leading to a KeyError.
+        del IOLoop._ioloop_for_asyncio[self.asyncio_loop]
+        self.asyncio_loop.close()
+
+    def add_handler(self, fd, handler, events):
+        fd, fileobj = self.split_fd(fd)
+        if fd in self.handlers:
+            raise ValueError("fd %s added twice" % fd)
+        self.handlers[fd] = (fileobj, stack_context.wrap(handler))
+        if events & IOLoop.READ:
+            self.asyncio_loop.add_reader(
+                fd, self._handle_events, fd, IOLoop.READ)
+            self.readers.add(fd)
+        if events & IOLoop.WRITE:
+            self.asyncio_loop.add_writer(
+                fd, self._handle_events, fd, IOLoop.WRITE)
+            self.writers.add(fd)
+
+    def update_handler(self, fd, events):
+        fd, fileobj = self.split_fd(fd)
+        if events & IOLoop.READ:
+            if fd not in self.readers:
+                self.asyncio_loop.add_reader(
+                    fd, self._handle_events, fd, IOLoop.READ)
+                self.readers.add(fd)
+        else:
+            if fd in self.readers:
+                self.asyncio_loop.remove_reader(fd)
+                self.readers.remove(fd)
+        if events & IOLoop.WRITE:
+            if fd not in self.writers:
+                self.asyncio_loop.add_writer(
+                    fd, self._handle_events, fd, IOLoop.WRITE)
+                self.writers.add(fd)
+        else:
+            if fd in self.writers:
+                self.asyncio_loop.remove_writer(fd)
+                self.writers.remove(fd)
+
+    def remove_handler(self, fd):
+        fd, fileobj = self.split_fd(fd)
+        if fd not in self.handlers:
+            return
+        if fd in self.readers:
+            self.asyncio_loop.remove_reader(fd)
+            self.readers.remove(fd)
+        if fd in self.writers:
+            self.asyncio_loop.remove_writer(fd)
+            self.writers.remove(fd)
+        del self.handlers[fd]
+
+    def _handle_events(self, fd, events):
+        fileobj, handler_func = self.handlers[fd]
+        handler_func(fileobj, events)
+
+    def start(self):
+        try:
+            old_loop = asyncio.get_event_loop()
+        except (RuntimeError, AssertionError):
+            old_loop = None
+        try:
+            self._setup_logging()
+            asyncio.set_event_loop(self.asyncio_loop)
+            self.asyncio_loop.run_forever()
+        finally:
+            asyncio.set_event_loop(old_loop)
+
+    def stop(self):
+        self.asyncio_loop.stop()
+
+    def call_at(self, when, callback, *args, **kwargs):
+        # asyncio.call_at supports *args but not **kwargs, so bind them here.
+        # We do not synchronize self.time and asyncio_loop.time, so
+        # convert from absolute to relative.
+        return self.asyncio_loop.call_later(
+            max(0, when - self.time()), self._run_callback,
+            functools.partial(stack_context.wrap(callback), *args, **kwargs))
+
+    def remove_timeout(self, timeout):
+        timeout.cancel()
+
+    def add_callback(self, callback, *args, **kwargs):
+        try:
+            self.asyncio_loop.call_soon_threadsafe(
+                self._run_callback,
+                functools.partial(stack_context.wrap(callback), *args, **kwargs))
+        except RuntimeError:
+            # "Event loop is closed". Swallow the exception for
+            # consistency with PollIOLoop (and logical consistency
+            # with the fact that we can't guarantee that an
+            # add_callback that completes without error will
+            # eventually execute).
+            pass
+
+    add_callback_from_signal = add_callback
+
+    def run_in_executor(self, executor, func, *args):
+        return self.asyncio_loop.run_in_executor(executor, func, *args)
+
+    def set_default_executor(self, executor):
+        return self.asyncio_loop.set_default_executor(executor)
+
+
+class AsyncIOMainLoop(BaseAsyncIOLoop):
+    """``AsyncIOMainLoop`` creates an `.IOLoop` that corresponds to the
+    current ``asyncio`` event loop (i.e. the one returned by
+    ``asyncio.get_event_loop()``).
+
+    .. deprecated:: 5.0
+
+       Now used automatically when appropriate; it is no longer necessary
+       to refer to this class directly.
+
+    .. versionchanged:: 5.0
+
+       Closing an `AsyncIOMainLoop` now closes the underlying asyncio loop.
+    """
+    def initialize(self, **kwargs):
+        super(AsyncIOMainLoop, self).initialize(asyncio.get_event_loop(), **kwargs)
+
+    def make_current(self):
+        # AsyncIOMainLoop already refers to the current asyncio loop so
+        # nothing to do here.
+        pass
+
+
+class AsyncIOLoop(BaseAsyncIOLoop):
+    """``AsyncIOLoop`` is an `.IOLoop` that runs on an ``asyncio`` event loop.
+    This class follows the usual Tornado semantics for creating new
+    ``IOLoops``; these loops are not necessarily related to the
+    ``asyncio`` default event loop.
+
+    Each ``AsyncIOLoop`` creates a new ``asyncio.EventLoop``; this object
+    can be accessed with the ``asyncio_loop`` attribute.
+
+    .. versionchanged:: 5.0
+
+       When an ``AsyncIOLoop`` becomes the current `.IOLoop`, it also sets
+       the current `asyncio` event loop.
+
+    .. deprecated:: 5.0
+
+       Now used automatically when appropriate; it is no longer necessary
+       to refer to this class directly.
+    """
+    def initialize(self, **kwargs):
+        self.is_current = False
+        loop = asyncio.new_event_loop()
+        try:
+            super(AsyncIOLoop, self).initialize(loop, **kwargs)
+        except Exception:
+            # If initialize() does not succeed (taking ownership of the loop),
+            # we have to close it.
+            loop.close()
+            raise
+
+    def close(self, all_fds=False):
+        if self.is_current:
+            self.clear_current()
+        super(AsyncIOLoop, self).close(all_fds=all_fds)
+
+    def make_current(self):
+        if not self.is_current:
+            try:
+                self.old_asyncio = asyncio.get_event_loop()
+            except (RuntimeError, AssertionError):
+                self.old_asyncio = None
+            self.is_current = True
+        asyncio.set_event_loop(self.asyncio_loop)
+
+    def _clear_current_hook(self):
+        if self.is_current:
+            asyncio.set_event_loop(self.old_asyncio)
+            self.is_current = False
+
+
+def to_tornado_future(asyncio_future):
+    """Convert an `asyncio.Future` to a `tornado.concurrent.Future`.
+
+    .. versionadded:: 4.1
+
+    .. deprecated:: 5.0
+       Tornado ``Futures`` have been merged with `asyncio.Future`,
+       so this method is now a no-op.
+    """
+    return asyncio_future
+
+
+def to_asyncio_future(tornado_future):
+    """Convert a Tornado yieldable object to an `asyncio.Future`.
+
+    .. versionadded:: 4.1
+
+    .. versionchanged:: 4.3
+       Now accepts any yieldable object, not just
+       `tornado.concurrent.Future`.
+
+    .. deprecated:: 5.0
+       Tornado ``Futures`` have been merged with `asyncio.Future`,
+       so this method is now equivalent to `tornado.gen.convert_yielded`.
+    """
+    return convert_yielded(tornado_future)
+
+
+class AnyThreadEventLoopPolicy(asyncio.DefaultEventLoopPolicy):
+    """Event loop policy that allows loop creation on any thread.
+
+    The default `asyncio` event loop policy only automatically creates
+    event loops in the main threads. Other threads must create event
+    loops explicitly or `asyncio.get_event_loop` (and therefore
+    `.IOLoop.current`) will fail. Installing this policy allows event
+    loops to be created automatically on any thread, matching the
+    behavior of Tornado versions prior to 5.0 (or 5.0 on Python 2).
+
+    Usage::
+
+        asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+
+    .. versionadded:: 5.0
+
+    """
+    def get_event_loop(self):
+        try:
+            return super().get_event_loop()
+        except (RuntimeError, AssertionError):
+            # This was an AssertionError in python 3.4.2 (which ships with debian jessie)
+            # and changed to a RuntimeError in 3.4.3.
+            # "There is no current event loop in thread %r"
+            loop = self.new_event_loop()
+            self.set_event_loop(loop)
+            return loop

lib/tornado/platform/auto.py

@@ -0,0 +1,58 @@
+#
+# Copyright 2011 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.
+
+"""Implementation of platform-specific functionality.
+
+For each function or class described in `tornado.platform.interface`,
+the appropriate platform-specific implementation exists in this module.
+Most code that needs access to this functionality should do e.g.::
+
+    from tornado.platform.auto import set_close_exec
+"""
+
+from __future__ import absolute_import, division, print_function
+
+import os
+
+if 'APPENGINE_RUNTIME' in os.environ:
+    from tornado.platform.common import Waker
+
+    def set_close_exec(fd):
+        pass
+elif os.name == 'nt':
+    from tornado.platform.common import Waker
+    from tornado.platform.windows import set_close_exec
+else:
+    from tornado.platform.posix import set_close_exec, Waker
+
+try:
+    # monotime monkey-patches the time module to have a monotonic function
+    # in versions of python before 3.3.
+    import monotime
+    # Silence pyflakes warning about this unused import
+    monotime
+except ImportError:
+    pass
+try:
+    # monotonic can provide a monotonic function in versions of python before
+    # 3.3, too.
+    from monotonic import monotonic as monotonic_time
+except ImportError:
+    try:
+        from time import monotonic as monotonic_time
+    except ImportError:
+        monotonic_time = None
+
+__all__ = ['Waker', 'set_close_exec', 'monotonic_time']

lib/tornado/platform/auto.pyi

@@ -0,0 +1,4 @@
+# auto.py is full of patterns mypy doesn't like, so for type checking
+# purposes we replace it with interface.py.
+
+from .interface import *

lib/tornado/platform/caresresolver.py

@@ -0,0 +1,79 @@
+from __future__ import absolute_import, division, print_function
+import pycares  # type: ignore
+import socket
+
+from tornado.concurrent import Future
+from tornado import gen
+from tornado.ioloop import IOLoop
+from tornado.netutil import Resolver, is_valid_ip
+
+
+class CaresResolver(Resolver):
+    """Name resolver based on the c-ares library.
+
+    This is a non-blocking and non-threaded resolver.  It may not produce
+    the same results as the system resolver, but can be used for non-blocking
+    resolution when threads cannot be used.
+
+    c-ares fails to resolve some names when ``family`` is ``AF_UNSPEC``,
+    so it is only recommended for use in ``AF_INET`` (i.e. IPv4).  This is
+    the default for ``tornado.simple_httpclient``, but other libraries
+    may default to ``AF_UNSPEC``.
+
+    .. versionchanged:: 5.0
+       The ``io_loop`` argument (deprecated since version 4.1) has been removed.
+    """
+    def initialize(self):
+        self.io_loop = IOLoop.current()
+        self.channel = pycares.Channel(sock_state_cb=self._sock_state_cb)
+        self.fds = {}
+
+    def _sock_state_cb(self, fd, readable, writable):
+        state = ((IOLoop.READ if readable else 0) |
+                 (IOLoop.WRITE if writable else 0))
+        if not state:
+            self.io_loop.remove_handler(fd)
+            del self.fds[fd]
+        elif fd in self.fds:
+            self.io_loop.update_handler(fd, state)
+            self.fds[fd] = state
+        else:
+            self.io_loop.add_handler(fd, self._handle_events, state)
+            self.fds[fd] = state
+
+    def _handle_events(self, fd, events):
+        read_fd = pycares.ARES_SOCKET_BAD
+        write_fd = pycares.ARES_SOCKET_BAD
+        if events & IOLoop.READ:
+            read_fd = fd
+        if events & IOLoop.WRITE:
+            write_fd = fd
+        self.channel.process_fd(read_fd, write_fd)
+
+    @gen.coroutine
+    def resolve(self, host, port, family=0):
+        if is_valid_ip(host):
+            addresses = [host]
+        else:
+            # gethostbyname doesn't take callback as a kwarg
+            fut = Future()
+            self.channel.gethostbyname(host, family,
+                                       lambda result, error: fut.set_result((result, error)))
+            result, error = yield fut
+            if error:
+                raise IOError('C-Ares returned error %s: %s while resolving %s' %
+                              (error, pycares.errno.strerror(error), host))
+            addresses = result.addresses
+        addrinfo = []
+        for address in addresses:
+            if '.' in address:
+                address_family = socket.AF_INET
+            elif ':' in address:
+                address_family = socket.AF_INET6
+            else:
+                address_family = socket.AF_UNSPEC
+            if family != socket.AF_UNSPEC and family != address_family:
+                raise IOError('Requested socket family %d but got %d' %
+                              (family, address_family))
+            addrinfo.append((address_family, (address, port)))
+        raise gen.Return(addrinfo)

lib/tornado/platform/common.py

@@ -0,0 +1,113 @@
+"""Lowest-common-denominator implementations of platform functionality."""
+from __future__ import absolute_import, division, print_function
+
+import errno
+import socket
+import time
+
+from tornado.platform import interface
+from tornado.util import errno_from_exception
+
+
+def try_close(f):
+    # Avoid issue #875 (race condition when using the file in another
+    # thread).
+    for i in range(10):
+        try:
+            f.close()
+        except IOError:
+            # Yield to another thread
+            time.sleep(1e-3)
+        else:
+            break
+    # Try a last time and let raise
+    f.close()
+
+
+class Waker(interface.Waker):
+    """Create an OS independent asynchronous pipe.
+
+    For use on platforms that don't have os.pipe() (or where pipes cannot
+    be passed to select()), but do have sockets.  This includes Windows
+    and Jython.
+    """
+    def __init__(self):
+        from .auto import set_close_exec
+        # Based on Zope select_trigger.py:
+        # https://github.com/zopefoundation/Zope/blob/master/src/ZServer/medusa/thread/select_trigger.py
+
+        self.writer = socket.socket()
+        set_close_exec(self.writer.fileno())
+        # Disable buffering -- pulling the trigger sends 1 byte,
+        # and we want that sent immediately, to wake up ASAP.
+        self.writer.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+
+        count = 0
+        while 1:
+            count += 1
+            # Bind to a local port; for efficiency, let the OS pick
+            # a free port for us.
+            # Unfortunately, stress tests showed that we may not
+            # be able to connect to that port ("Address already in
+            # use") despite that the OS picked it.  This appears
+            # to be a race bug in the Windows socket implementation.
+            # So we loop until a connect() succeeds (almost always
+            # on the first try).  See the long thread at
+            # http://mail.zope.org/pipermail/zope/2005-July/160433.html
+            # for hideous details.
+            a = socket.socket()
+            set_close_exec(a.fileno())
+            a.bind(("127.0.0.1", 0))
+            a.listen(1)
+            connect_address = a.getsockname()  # assigned (host, port) pair
+            try:
+                self.writer.connect(connect_address)
+                break    # success
+            except socket.error as detail:
+                if (not hasattr(errno, 'WSAEADDRINUSE') or
+                        errno_from_exception(detail) != errno.WSAEADDRINUSE):
+                    # "Address already in use" is the only error
+                    # I've seen on two WinXP Pro SP2 boxes, under
+                    # Pythons 2.3.5 and 2.4.1.
+                    raise
+                # (10048, 'Address already in use')
+                # assert count <= 2 # never triggered in Tim's tests
+                if count >= 10:  # I've never seen it go above 2
+                    a.close()
+                    self.writer.close()
+                    raise socket.error("Cannot bind trigger!")
+                # Close `a` and try again.  Note:  I originally put a short
+                # sleep() here, but it didn't appear to help or hurt.
+                a.close()
+
+        self.reader, addr = a.accept()
+        set_close_exec(self.reader.fileno())
+        self.reader.setblocking(0)
+        self.writer.setblocking(0)
+        a.close()
+        self.reader_fd = self.reader.fileno()
+
+    def fileno(self):
+        return self.reader.fileno()
+
+    def write_fileno(self):
+        return self.writer.fileno()
+
+    def wake(self):
+        try:
+            self.writer.send(b"x")
+        except (IOError, socket.error, ValueError):
+            pass
+
+    def consume(self):
+        try:
+            while True:
+                result = self.reader.recv(1024)
+                if not result:
+                    break
+        except (IOError, socket.error):
+            pass
+
+    def close(self):
+        self.reader.close()
+        try_close(self.writer)

lib/tornado/platform/epoll.py

@@ -0,0 +1,25 @@
+#
+# 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.
+"""EPoll-based IOLoop implementation for Linux systems."""
+from __future__ import absolute_import, division, print_function
+
+import select
+
+from tornado.ioloop import PollIOLoop
+
+
+class EPollIOLoop(PollIOLoop):
+    def initialize(self, **kwargs):
+        super(EPollIOLoop, self).initialize(impl=select.epoll(), **kwargs)

lib/tornado/platform/interface.py

@@ -0,0 +1,66 @@
+#
+# Copyright 2011 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.
+
+"""Interfaces for platform-specific functionality.
+
+This module exists primarily for documentation purposes and as base classes
+for other tornado.platform modules.  Most code should import the appropriate
+implementation from `tornado.platform.auto`.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+
+def set_close_exec(fd):
+    """Sets the close-on-exec bit (``FD_CLOEXEC``)for a file descriptor."""
+    raise NotImplementedError()
+
+
+class Waker(object):
+    """A socket-like object that can wake another thread from ``select()``.
+
+    The `~tornado.ioloop.IOLoop` will add the Waker's `fileno()` to
+    its ``select`` (or ``epoll`` or ``kqueue``) calls.  When another
+    thread wants to wake up the loop, it calls `wake`.  Once it has woken
+    up, it will call `consume` to do any necessary per-wake cleanup.  When
+    the ``IOLoop`` is closed, it closes its waker too.
+    """
+    def fileno(self):
+        """Returns the read file descriptor for this waker.
+
+        Must be suitable for use with ``select()`` or equivalent on the
+        local platform.
+        """
+        raise NotImplementedError()
+
+    def write_fileno(self):
+        """Returns the write file descriptor for this waker."""
+        raise NotImplementedError()
+
+    def wake(self):
+        """Triggers activity on the waker's file descriptor."""
+        raise NotImplementedError()
+
+    def consume(self):
+        """Called after the listen has woken up to do any necessary cleanup."""
+        raise NotImplementedError()
+
+    def close(self):
+        """Closes the waker's file descriptor(s)."""
+        raise NotImplementedError()
+
+
+def monotonic_time():
+    raise NotImplementedError()

lib/tornado/platform/kqueue.py

@@ -0,0 +1,90 @@
+#
+# 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.
+"""KQueue-based IOLoop implementation for BSD/Mac systems."""
+from __future__ import absolute_import, division, print_function
+
+import select
+
+from tornado.ioloop import IOLoop, PollIOLoop
+
+assert hasattr(select, 'kqueue'), 'kqueue not supported'
+
+
+class _KQueue(object):
+    """A kqueue-based event loop for BSD/Mac systems."""
+    def __init__(self):
+        self._kqueue = select.kqueue()
+        self._active = {}
+
+    def fileno(self):
+        return self._kqueue.fileno()
+
+    def close(self):
+        self._kqueue.close()
+
+    def register(self, fd, events):
+        if fd in self._active:
+            raise IOError("fd %s already registered" % fd)
+        self._control(fd, events, select.KQ_EV_ADD)
+        self._active[fd] = events
+
+    def modify(self, fd, events):
+        self.unregister(fd)
+        self.register(fd, events)
+
+    def unregister(self, fd):
+        events = self._active.pop(fd)
+        self._control(fd, events, select.KQ_EV_DELETE)
+
+    def _control(self, fd, events, flags):
+        kevents = []
+        if events & IOLoop.WRITE:
+            kevents.append(select.kevent(
+                fd, filter=select.KQ_FILTER_WRITE, flags=flags))
+        if events & IOLoop.READ:
+            kevents.append(select.kevent(
+                fd, filter=select.KQ_FILTER_READ, flags=flags))
+        # Even though control() takes a list, it seems to return EINVAL
+        # on Mac OS X (10.6) when there is more than one event in the list.
+        for kevent in kevents:
+            self._kqueue.control([kevent], 0)
+
+    def poll(self, timeout):
+        kevents = self._kqueue.control(None, 1000, timeout)
+        events = {}
+        for kevent in kevents:
+            fd = kevent.ident
+            if kevent.filter == select.KQ_FILTER_READ:
+                events[fd] = events.get(fd, 0) | IOLoop.READ
+            if kevent.filter == select.KQ_FILTER_WRITE:
+                if kevent.flags & select.KQ_EV_EOF:
+                    # If an asynchronous connection is refused, kqueue
+                    # returns a write event with the EOF flag set.
+                    # Turn this into an error for consistency with the
+                    # other IOLoop implementations.
+                    # Note that for read events, EOF may be returned before
+                    # all data has been consumed from the socket buffer,
+                    # so we only check for EOF on write events.
+                    events[fd] = IOLoop.ERROR
+                else:
+                    events[fd] = events.get(fd, 0) | IOLoop.WRITE
+            if kevent.flags & select.KQ_EV_ERROR:
+                events[fd] = events.get(fd, 0) | IOLoop.ERROR
+        return events.items()
+
+
+class KQueueIOLoop(PollIOLoop):
+    def initialize(self, **kwargs):
+        super(KQueueIOLoop, self).initialize(impl=_KQueue(), **kwargs)

lib/tornado/platform/posix.py

@@ -0,0 +1,69 @@
+#
+# Copyright 2011 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.
+
+"""Posix implementations of platform-specific functionality."""
+
+from __future__ import absolute_import, division, print_function
+
+import fcntl
+import os
+
+from tornado.platform import common, interface
+
+
+def set_close_exec(fd):
+    flags = fcntl.fcntl(fd, fcntl.F_GETFD)
+    fcntl.fcntl(fd, fcntl.F_SETFD, flags | fcntl.FD_CLOEXEC)
+
+
+def _set_nonblocking(fd):
+    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
+    fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
+
+
+class Waker(interface.Waker):
+    def __init__(self):
+        r, w = os.pipe()
+        _set_nonblocking(r)
+        _set_nonblocking(w)
+        set_close_exec(r)
+        set_close_exec(w)
+        self.reader = os.fdopen(r, "rb", 0)
+        self.writer = os.fdopen(w, "wb", 0)
+
+    def fileno(self):
+        return self.reader.fileno()
+
+    def write_fileno(self):
+        return self.writer.fileno()
+
+    def wake(self):
+        try:
+            self.writer.write(b"x")
+        except (IOError, ValueError):
+            pass
+
+    def consume(self):
+        try:
+            while True:
+                result = self.reader.read()
+                if not result:
+                    break
+        except IOError:
+            pass
+
+    def close(self):
+        self.reader.close()
+        common.try_close(self.writer)

lib/tornado/platform/select.py

@@ -0,0 +1,75 @@
+#
+# 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
+
+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)

lib/tornado/platform/twisted.py

@@ -0,0 +1,609 @@
+# Author: Ovidiu Predescu
+# Date: July 2011
+#
+# 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.
+"""Bridges between the Twisted reactor and Tornado IOLoop.
+
+This module lets you run applications and libraries written for
+Twisted in a Tornado application.  It can be used in two modes,
+depending on which library's underlying event loop you want to use.
+
+This module has been tested with Twisted versions 11.0.0 and newer.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+import datetime
+import functools
+import numbers
+import socket
+import sys
+
+import twisted.internet.abstract  # type: ignore
+from twisted.internet.defer import Deferred  # type: ignore
+from twisted.internet.posixbase import PosixReactorBase  # type: ignore
+from twisted.internet.interfaces import IReactorFDSet, IDelayedCall, IReactorTime, IReadDescriptor, IWriteDescriptor  # type: ignore # noqa: E501
+from twisted.python import failure, log  # type: ignore
+from twisted.internet import error  # type: ignore
+import twisted.names.cache  # type: ignore
+import twisted.names.client  # type: ignore
+import twisted.names.hosts  # type: ignore
+import twisted.names.resolve  # type: ignore
+
+from zope.interface import implementer  # type: ignore
+
+from tornado.concurrent import Future, future_set_exc_info
+from tornado.escape import utf8
+from tornado import gen
+import tornado.ioloop
+from tornado.log import app_log
+from tornado.netutil import Resolver
+from tornado.stack_context import NullContext, wrap
+from tornado.ioloop import IOLoop
+from tornado.util import timedelta_to_seconds
+
+
+@implementer(IDelayedCall)
+class TornadoDelayedCall(object):
+    """DelayedCall object for Tornado."""
+    def __init__(self, reactor, seconds, f, *args, **kw):
+        self._reactor = reactor
+        self._func = functools.partial(f, *args, **kw)
+        self._time = self._reactor.seconds() + seconds
+        self._timeout = self._reactor._io_loop.add_timeout(self._time,
+                                                           self._called)
+        self._active = True
+
+    def _called(self):
+        self._active = False
+        self._reactor._removeDelayedCall(self)
+        try:
+            self._func()
+        except:
+            app_log.error("_called caught exception", exc_info=True)
+
+    def getTime(self):
+        return self._time
+
+    def cancel(self):
+        self._active = False
+        self._reactor._io_loop.remove_timeout(self._timeout)
+        self._reactor._removeDelayedCall(self)
+
+    def delay(self, seconds):
+        self._reactor._io_loop.remove_timeout(self._timeout)
+        self._time += seconds
+        self._timeout = self._reactor._io_loop.add_timeout(self._time,
+                                                           self._called)
+
+    def reset(self, seconds):
+        self._reactor._io_loop.remove_timeout(self._timeout)
+        self._time = self._reactor.seconds() + seconds
+        self._timeout = self._reactor._io_loop.add_timeout(self._time,
+                                                           self._called)
+
+    def active(self):
+        return self._active
+
+
+@implementer(IReactorTime, IReactorFDSet)
+class TornadoReactor(PosixReactorBase):
+    """Twisted reactor built on the Tornado IOLoop.
+
+    `TornadoReactor` implements the Twisted reactor interface on top of
+    the Tornado IOLoop.  To use it, simply call `install` at the beginning
+    of the application::
+
+        import tornado.platform.twisted
+        tornado.platform.twisted.install()
+        from twisted.internet import reactor
+
+    When the app is ready to start, call ``IOLoop.current().start()``
+    instead of ``reactor.run()``.
+
+    It is also possible to create a non-global reactor by calling
+    ``tornado.platform.twisted.TornadoReactor()``.  However, if
+    the `.IOLoop` and reactor are to be short-lived (such as those used in
+    unit tests), additional cleanup may be required.  Specifically, it is
+    recommended to call::
+
+        reactor.fireSystemEvent('shutdown')
+        reactor.disconnectAll()
+
+    before closing the `.IOLoop`.
+
+    .. versionchanged:: 5.0
+       The ``io_loop`` argument (deprecated since version 4.1) has been removed.
+
+    .. deprecated:: 5.1
+
+       This class will be removed in Tornado 6.0. Use
+       ``twisted.internet.asyncioreactor.AsyncioSelectorReactor``
+       instead.
+
+    """
+    def __init__(self):
+        self._io_loop = tornado.ioloop.IOLoop.current()
+        self._readers = {}  # map of reader objects to fd
+        self._writers = {}  # map of writer objects to fd
+        self._fds = {}  # a map of fd to a (reader, writer) tuple
+        self._delayedCalls = {}
+        PosixReactorBase.__init__(self)
+        self.addSystemEventTrigger('during', 'shutdown', self.crash)
+
+        # IOLoop.start() bypasses some of the reactor initialization.
+        # Fire off the necessary events if they weren't already triggered
+        # by reactor.run().
+        def start_if_necessary():
+            if not self._started:
+                self.fireSystemEvent('startup')
+        self._io_loop.add_callback(start_if_necessary)
+
+    # IReactorTime
+    def seconds(self):
+        return self._io_loop.time()
+
+    def callLater(self, seconds, f, *args, **kw):
+        dc = TornadoDelayedCall(self, seconds, f, *args, **kw)
+        self._delayedCalls[dc] = True
+        return dc
+
+    def getDelayedCalls(self):
+        return [x for x in self._delayedCalls if x._active]
+
+    def _removeDelayedCall(self, dc):
+        if dc in self._delayedCalls:
+            del self._delayedCalls[dc]
+
+    # IReactorThreads
+    def callFromThread(self, f, *args, **kw):
+        assert callable(f), "%s is not callable" % f
+        with NullContext():
+            # This NullContext is mainly for an edge case when running
+            # TwistedIOLoop on top of a TornadoReactor.
+            # TwistedIOLoop.add_callback uses reactor.callFromThread and
+            # should not pick up additional StackContexts along the way.
+            self._io_loop.add_callback(f, *args, **kw)
+
+    # We don't need the waker code from the super class, Tornado uses
+    # its own waker.
+    def installWaker(self):
+        pass
+
+    def wakeUp(self):
+        pass
+
+    # IReactorFDSet
+    def _invoke_callback(self, fd, events):
+        if fd not in self._fds:
+            return
+        (reader, writer) = self._fds[fd]
+        if reader:
+            err = None
+            if reader.fileno() == -1:
+                err = error.ConnectionLost()
+            elif events & IOLoop.READ:
+                err = log.callWithLogger(reader, reader.doRead)
+            if err is None and events & IOLoop.ERROR:
+                err = error.ConnectionLost()
+            if err is not None:
+                self.removeReader(reader)
+                reader.readConnectionLost(failure.Failure(err))
+        if writer:
+            err = None
+            if writer.fileno() == -1:
+                err = error.ConnectionLost()
+            elif events & IOLoop.WRITE:
+                err = log.callWithLogger(writer, writer.doWrite)
+            if err is None and events & IOLoop.ERROR:
+                err = error.ConnectionLost()
+            if err is not None:
+                self.removeWriter(writer)
+                writer.writeConnectionLost(failure.Failure(err))
+
+    def addReader(self, reader):
+        if reader in self._readers:
+            # Don't add the reader if it's already there
+            return
+        fd = reader.fileno()
+        self._readers[reader] = fd
+        if fd in self._fds:
+            (_, writer) = self._fds[fd]
+            self._fds[fd] = (reader, writer)
+            if writer:
+                # We already registered this fd for write events,
+                # update it for read events as well.
+                self._io_loop.update_handler(fd, IOLoop.READ | IOLoop.WRITE)
+        else:
+            with NullContext():
+                self._fds[fd] = (reader, None)
+                self._io_loop.add_handler(fd, self._invoke_callback,
+                                          IOLoop.READ)
+
+    def addWriter(self, writer):
+        if writer in self._writers:
+            return
+        fd = writer.fileno()
+        self._writers[writer] = fd
+        if fd in self._fds:
+            (reader, _) = self._fds[fd]
+            self._fds[fd] = (reader, writer)
+            if reader:
+                # We already registered this fd for read events,
+                # update it for write events as well.
+                self._io_loop.update_handler(fd, IOLoop.READ | IOLoop.WRITE)
+        else:
+            with NullContext():
+                self._fds[fd] = (None, writer)
+                self._io_loop.add_handler(fd, self._invoke_callback,
+                                          IOLoop.WRITE)
+
+    def removeReader(self, reader):
+        if reader in self._readers:
+            fd = self._readers.pop(reader)
+            (_, writer) = self._fds[fd]
+            if writer:
+                # We have a writer so we need to update the IOLoop for
+                # write events only.
+                self._fds[fd] = (None, writer)
+                self._io_loop.update_handler(fd, IOLoop.WRITE)
+            else:
+                # Since we have no writer registered, we remove the
+                # entry from _fds and unregister the handler from the
+                # IOLoop
+                del self._fds[fd]
+                self._io_loop.remove_handler(fd)
+
+    def removeWriter(self, writer):
+        if writer in self._writers:
+            fd = self._writers.pop(writer)
+            (reader, _) = self._fds[fd]
+            if reader:
+                # We have a reader so we need to update the IOLoop for
+                # read events only.
+                self._fds[fd] = (reader, None)
+                self._io_loop.update_handler(fd, IOLoop.READ)
+            else:
+                # Since we have no reader registered, we remove the
+                # entry from the _fds and unregister the handler from
+                # the IOLoop.
+                del self._fds[fd]
+                self._io_loop.remove_handler(fd)
+
+    def removeAll(self):
+        return self._removeAll(self._readers, self._writers)
+
+    def getReaders(self):
+        return self._readers.keys()
+
+    def getWriters(self):
+        return self._writers.keys()
+
+    # The following functions are mainly used in twisted-style test cases;
+    # it is expected that most users of the TornadoReactor will call
+    # IOLoop.start() instead of Reactor.run().
+    def stop(self):
+        PosixReactorBase.stop(self)
+        fire_shutdown = functools.partial(self.fireSystemEvent, "shutdown")
+        self._io_loop.add_callback(fire_shutdown)
+
+    def crash(self):
+        PosixReactorBase.crash(self)
+        self._io_loop.stop()
+
+    def doIteration(self, delay):
+        raise NotImplementedError("doIteration")
+
+    def mainLoop(self):
+        # Since this class is intended to be used in applications
+        # where the top-level event loop is ``io_loop.start()`` rather
+        # than ``reactor.run()``, it is implemented a little
+        # differently than other Twisted reactors. We override
+        # ``mainLoop`` instead of ``doIteration`` and must implement
+        # timed call functionality on top of `.IOLoop.add_timeout`
+        # rather than using the implementation in
+        # ``PosixReactorBase``.
+        self._io_loop.start()
+
+
+class _TestReactor(TornadoReactor):
+    """Subclass of TornadoReactor for use in unittests.
+
+    This can't go in the test.py file because of import-order dependencies
+    with the Twisted reactor test builder.
+    """
+    def __init__(self):
+        # always use a new ioloop
+        IOLoop.clear_current()
+        IOLoop(make_current=True)
+        super(_TestReactor, self).__init__()
+        IOLoop.clear_current()
+
+    def listenTCP(self, port, factory, backlog=50, interface=''):
+        # default to localhost to avoid firewall prompts on the mac
+        if not interface:
+            interface = '127.0.0.1'
+        return super(_TestReactor, self).listenTCP(
+            port, factory, backlog=backlog, interface=interface)
+
+    def listenUDP(self, port, protocol, interface='', maxPacketSize=8192):
+        if not interface:
+            interface = '127.0.0.1'
+        return super(_TestReactor, self).listenUDP(
+            port, protocol, interface=interface, maxPacketSize=maxPacketSize)
+
+
+def install():
+    """Install this package as the default Twisted reactor.
+
+    ``install()`` must be called very early in the startup process,
+    before most other twisted-related imports. Conversely, because it
+    initializes the `.IOLoop`, it cannot be called before
+    `.fork_processes` or multi-process `~.TCPServer.start`. These
+    conflicting requirements make it difficult to use `.TornadoReactor`
+    in multi-process mode, and an external process manager such as
+    ``supervisord`` is recommended instead.
+
+    .. versionchanged:: 5.0
+       The ``io_loop`` argument (deprecated since version 4.1) has been removed.
+
+    .. deprecated:: 5.1
+
+       This functio will be removed in Tornado 6.0. Use
+       ``twisted.internet.asyncioreactor.install`` instead.
+    """
+    reactor = TornadoReactor()
+    from twisted.internet.main import installReactor  # type: ignore
+    installReactor(reactor)
+    return reactor
+
+
+@implementer(IReadDescriptor, IWriteDescriptor)
+class _FD(object):
+    def __init__(self, fd, fileobj, handler):
+        self.fd = fd
+        self.fileobj = fileobj
+        self.handler = handler
+        self.reading = False
+        self.writing = False
+        self.lost = False
+
+    def fileno(self):
+        return self.fd
+
+    def doRead(self):
+        if not self.lost:
+            self.handler(self.fileobj, tornado.ioloop.IOLoop.READ)
+
+    def doWrite(self):
+        if not self.lost:
+            self.handler(self.fileobj, tornado.ioloop.IOLoop.WRITE)
+
+    def connectionLost(self, reason):
+        if not self.lost:
+            self.handler(self.fileobj, tornado.ioloop.IOLoop.ERROR)
+            self.lost = True
+
+    writeConnectionLost = readConnectionLost = connectionLost
+
+    def logPrefix(self):
+        return ''
+
+
+class TwistedIOLoop(tornado.ioloop.IOLoop):
+    """IOLoop implementation that runs on Twisted.
+
+    `TwistedIOLoop` implements the Tornado IOLoop interface on top of
+    the Twisted reactor. Recommended usage::
+
+        from tornado.platform.twisted import TwistedIOLoop
+        from twisted.internet import reactor
+        TwistedIOLoop().install()
+        # Set up your tornado application as usual using `IOLoop.instance`
+        reactor.run()
+
+    Uses the global Twisted reactor by default.  To create multiple
+    ``TwistedIOLoops`` in the same process, you must pass a unique reactor
+    when constructing each one.
+
+    Not compatible with `tornado.process.Subprocess.set_exit_callback`
+    because the ``SIGCHLD`` handlers used by Tornado and Twisted conflict
+    with each other.
+
+    See also :meth:`tornado.ioloop.IOLoop.install` for general notes on
+    installing alternative IOLoops.
+
+    .. deprecated:: 5.1
+
+       The `asyncio` event loop will be the only available implementation in
+       Tornado 6.0.
+    """
+    def initialize(self, reactor=None, **kwargs):
+        super(TwistedIOLoop, self).initialize(**kwargs)
+        if reactor is None:
+            import twisted.internet.reactor  # type: ignore
+            reactor = twisted.internet.reactor
+        self.reactor = reactor
+        self.fds = {}
+
+    def close(self, all_fds=False):
+        fds = self.fds
+        self.reactor.removeAll()
+        for c in self.reactor.getDelayedCalls():
+            c.cancel()
+        if all_fds:
+            for fd in fds.values():
+                self.close_fd(fd.fileobj)
+
+    def add_handler(self, fd, handler, events):
+        if fd in self.fds:
+            raise ValueError('fd %s added twice' % fd)
+        fd, fileobj = self.split_fd(fd)
+        self.fds[fd] = _FD(fd, fileobj, wrap(handler))
+        if events & tornado.ioloop.IOLoop.READ:
+            self.fds[fd].reading = True
+            self.reactor.addReader(self.fds[fd])
+        if events & tornado.ioloop.IOLoop.WRITE:
+            self.fds[fd].writing = True
+            self.reactor.addWriter(self.fds[fd])
+
+    def update_handler(self, fd, events):
+        fd, fileobj = self.split_fd(fd)
+        if events & tornado.ioloop.IOLoop.READ:
+            if not self.fds[fd].reading:
+                self.fds[fd].reading = True
+                self.reactor.addReader(self.fds[fd])
+        else:
+            if self.fds[fd].reading:
+                self.fds[fd].reading = False
+                self.reactor.removeReader(self.fds[fd])
+        if events & tornado.ioloop.IOLoop.WRITE:
+            if not self.fds[fd].writing:
+                self.fds[fd].writing = True
+                self.reactor.addWriter(self.fds[fd])
+        else:
+            if self.fds[fd].writing:
+                self.fds[fd].writing = False
+                self.reactor.removeWriter(self.fds[fd])
+
+    def remove_handler(self, fd):
+        fd, fileobj = self.split_fd(fd)
+        if fd not in self.fds:
+            return
+        self.fds[fd].lost = True
+        if self.fds[fd].reading:
+            self.reactor.removeReader(self.fds[fd])
+        if self.fds[fd].writing:
+            self.reactor.removeWriter(self.fds[fd])
+        del self.fds[fd]
+
+    def start(self):
+        old_current = IOLoop.current(instance=False)
+        try:
+            self._setup_logging()
+            self.make_current()
+            self.reactor.run()
+        finally:
+            if old_current is None:
+                IOLoop.clear_current()
+            else:
+                old_current.make_current()
+
+    def stop(self):
+        self.reactor.crash()
+
+    def add_timeout(self, deadline, callback, *args, **kwargs):
+        # This method could be simplified (since tornado 4.0) by
+        # overriding call_at instead of add_timeout, but we leave it
+        # for now as a test of backwards-compatibility.
+        if isinstance(deadline, numbers.Real):
+            delay = max(deadline - self.time(), 0)
+        elif isinstance(deadline, datetime.timedelta):
+            delay = timedelta_to_seconds(deadline)
+        else:
+            raise TypeError("Unsupported deadline %r")
+        return self.reactor.callLater(
+            delay, self._run_callback,
+            functools.partial(wrap(callback), *args, **kwargs))
+
+    def remove_timeout(self, timeout):
+        if timeout.active():
+            timeout.cancel()
+
+    def add_callback(self, callback, *args, **kwargs):
+        self.reactor.callFromThread(
+            self._run_callback,
+            functools.partial(wrap(callback), *args, **kwargs))
+
+    def add_callback_from_signal(self, callback, *args, **kwargs):
+        self.add_callback(callback, *args, **kwargs)
+
+
+class TwistedResolver(Resolver):
+    """Twisted-based asynchronous resolver.
+
+    This is a non-blocking and non-threaded resolver.  It is
+    recommended only when threads cannot be used, since it has
+    limitations compared to the standard ``getaddrinfo``-based
+    `~tornado.netutil.Resolver` and
+    `~tornado.netutil.DefaultExecutorResolver`.  Specifically, it returns at
+    most one result, and arguments other than ``host`` and ``family``
+    are ignored.  It may fail to resolve when ``family`` is not
+    ``socket.AF_UNSPEC``.
+
+    Requires Twisted 12.1 or newer.
+
+    .. versionchanged:: 5.0
+       The ``io_loop`` argument (deprecated since version 4.1) has been removed.
+    """
+    def initialize(self):
+        # partial copy of twisted.names.client.createResolver, which doesn't
+        # allow for a reactor to be passed in.
+        self.reactor = tornado.platform.twisted.TornadoReactor()
+
+        host_resolver = twisted.names.hosts.Resolver('/etc/hosts')
+        cache_resolver = twisted.names.cache.CacheResolver(reactor=self.reactor)
+        real_resolver = twisted.names.client.Resolver('/etc/resolv.conf',
+                                                      reactor=self.reactor)
+        self.resolver = twisted.names.resolve.ResolverChain(
+            [host_resolver, cache_resolver, real_resolver])
+
+    @gen.coroutine
+    def resolve(self, host, port, family=0):
+        # getHostByName doesn't accept IP addresses, so if the input
+        # looks like an IP address just return it immediately.
+        if twisted.internet.abstract.isIPAddress(host):
+            resolved = host
+            resolved_family = socket.AF_INET
+        elif twisted.internet.abstract.isIPv6Address(host):
+            resolved = host
+            resolved_family = socket.AF_INET6
+        else:
+            deferred = self.resolver.getHostByName(utf8(host))
+            fut = Future()
+            deferred.addBoth(fut.set_result)
+            resolved = yield fut
+            if isinstance(resolved, failure.Failure):
+                try:
+                    resolved.raiseException()
+                except twisted.names.error.DomainError as e:
+                    raise IOError(e)
+            elif twisted.internet.abstract.isIPAddress(resolved):
+                resolved_family = socket.AF_INET
+            elif twisted.internet.abstract.isIPv6Address(resolved):
+                resolved_family = socket.AF_INET6
+            else:
+                resolved_family = socket.AF_UNSPEC
+        if family != socket.AF_UNSPEC and family != resolved_family:
+            raise Exception('Requested socket family %d but got %d' %
+                            (family, resolved_family))
+        result = [
+            (resolved_family, (resolved, port)),
+        ]
+        raise gen.Return(result)
+
+
+if hasattr(gen.convert_yielded, 'register'):
+    @gen.convert_yielded.register(Deferred)  # type: ignore
+    def _(d):
+        f = Future()
+
+        def errback(failure):
+            try:
+                failure.raiseException()
+                # Should never happen, but just in case
+                raise Exception("errback called without error")
+            except:
+                future_set_exc_info(f, sys.exc_info())
+        d.addCallbacks(f.set_result, errback)
+        return f

lib/tornado/platform/windows.py

@@ -0,0 +1,20 @@
+# NOTE: win32 support is currently experimental, and not recommended
+# for production use.
+
+
+from __future__ import absolute_import, division, print_function
+import ctypes  # type: ignore
+import ctypes.wintypes  # type: ignore
+
+# See: http://msdn.microsoft.com/en-us/library/ms724935(VS.85).aspx
+SetHandleInformation = ctypes.windll.kernel32.SetHandleInformation
+SetHandleInformation.argtypes = (ctypes.wintypes.HANDLE, ctypes.wintypes.DWORD, ctypes.wintypes.DWORD)  # noqa: E501
+SetHandleInformation.restype = ctypes.wintypes.BOOL
+
+HANDLE_FLAG_INHERIT = 0x00000001
+
+
+def set_close_exec(fd):
+    success = SetHandleInformation(fd, HANDLE_FLAG_INHERIT, 0)
+    if not success:
+        raise ctypes.WinError()