# Source code for tornado.ioloop

    #
    # Copyright 2009 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.

    """An I/O event loop for non-blocking sockets.

    In Tornado 6.0, `.IOLoop` is a wrapper around the `asyncio` event
    loop, with a slightly different interface for historical reasons.
    Applications can use either the `.IOLoop` interface or the underlying
    `asyncio` event loop directly (unless compatibility with older
    versions of Tornado is desired, in which case `.IOLoop` must be used).

    Typical applications will use a single `IOLoop` object, accessed via
    `IOLoop.current` class method. The `IOLoop.start` method (or
    equivalently, `asyncio.AbstractEventLoop.run_forever`) should usually
    be called at the end of the ``main()`` function. Atypical applications
    may use more than one `IOLoop`, such as one `IOLoop` per thread, or
    per `unittest` case.

    """

    import asyncio
    import concurrent.futures
    import datetime
    import functools
    import logging
    import numbers
    import os
    import sys
    import time
    import math
    import random

    from tornado.concurrent import (
        Future,
        is_future,
        chain_future,
        future_set_exc_info,
        future_add_done_callback,
    )
    from tornado.log import app_log
    from tornado.util import Configurable, TimeoutError, import_object

    import typing
    from typing import Union, Any, Type, Optional, Callable, TypeVar, Tuple, Awaitable

    if typing.TYPE_CHECKING:
        from typing import Dict, List  # noqa: F401

        from typing_extensions import Protocol
    else:
        Protocol = object

    class _Selectable(Protocol):
        def fileno(self) -> int:
            pass

        def close(self) -> None:
            pass

    _T = TypeVar("_T")
    _S = TypeVar("_S", bound=_Selectable)

    class IOLoop(Configurable):
        """An I/O event loop.

        As of Tornado 6.0, `IOLoop` is a wrapper around the `asyncio` event
        loop.

        Example usage for a simple TCP server:

        .. testcode::

            import errno
            import functools
            import socket

            import tornado.ioloop
            from tornado.iostream import IOStream

            async def handle_connection(connection, address):
                stream = IOStream(connection)
                message = await stream.read_until_close()
                print("message from client:", message.decode().strip())

            def connection_ready(sock, fd, events):
                while True:
                    try:
                        connection, address = sock.accept()
                    except BlockingIOError:
                        return
                    connection.setblocking(0)
                    io_loop = tornado.ioloop.IOLoop.current()
                    io_loop.spawn_callback(handle_connection, connection, address)

            if __name__ == '__main__':
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
                sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                sock.setblocking(0)
                sock.bind(("", 8888))
                sock.listen(128)

                io_loop = tornado.ioloop.IOLoop.current()
                callback = functools.partial(connection_ready, sock)
                io_loop.add_handler(sock.fileno(), callback, io_loop.READ)
                io_loop.start()

        .. testoutput::
           :hide:

        By default, a newly-constructed `IOLoop` becomes the thread's current
        `IOLoop`, unless there already is a current `IOLoop`. This behavior
        can be controlled with the ``make_current`` argument to the `IOLoop`
        constructor: if ``make_current=True``, the new `IOLoop` will always
        try to become current and it raises an error if there is already a
        current instance. If ``make_current=False``, the new `IOLoop` will
        not try to become current.

        In general, an `IOLoop` cannot survive a fork or be shared across
        processes in any way. When multiple processes are being used, each
        process should create its own `IOLoop`, which also implies that
        any objects which depend on the `IOLoop` (such as
        `.AsyncHTTPClient`) must also be created in the child processes.
        As a guideline, anything that starts processes (including the
        `tornado.process` and `multiprocessing` modules) should do so as
        early as possible, ideally the first thing the application does
        after loading its configuration in ``main()``.

        .. versionchanged:: 4.2
           Added the ``make_current`` keyword argument to the `IOLoop`
           constructor.

        .. versionchanged:: 5.0

           Uses the `asyncio` event loop by default. The
           ``IOLoop.configure`` method cannot be used on Python 3 except
           to redundantly specify the `asyncio` event loop.

        """

        # These constants were originally based on constants from the epoll module.
        NONE = 0
        READ = 0x001
        WRITE = 0x004
        ERROR = 0x018

        # In Python 3, _ioloop_for_asyncio maps from asyncio loops to IOLoops.
        _ioloop_for_asyncio = dict()  # type: Dict[asyncio.AbstractEventLoop, IOLoop]

        @classmethod
        def configure(
            cls, impl: "Union[None, str, Type[Configurable]]", **kwargs: Any
        ) -> None:
            if asyncio is not None:
                from tornado.platform.asyncio import BaseAsyncIOLoop

                if isinstance(impl, str):
                    impl = import_object(impl)
                if isinstance(impl, type) and not issubclass(impl, BaseAsyncIOLoop):
                    raise RuntimeError(
                        "only AsyncIOLoop is allowed when asyncio is available"
                    )
            super(IOLoop, cls).configure(impl, **kwargs)

        @staticmethod
        def instance() -> "IOLoop":
            """Deprecated alias for `IOLoop.current()`.

            .. versionchanged:: 5.0

               Previously, this method returned a global singleton
               `IOLoop`, in contrast with the per-thread `IOLoop` returned
               by `current()`. In nearly all cases the two were the same
               (when they differed, it was generally used from non-Tornado
               threads to communicate back to the main thread's `IOLoop`).
               This distinction is not present in `asyncio`, so in order
               to facilitate integration with that package `instance()`
               was changed to be an alias to `current()`. Applications
               using the cross-thread communications aspect of
               `instance()` should instead set their own global variable
               to point to the `IOLoop` they want to use.

            .. deprecated:: 5.0
            """
            return IOLoop.current()

        def install(self) -> None:
            """Deprecated alias for `make_current()`.

            .. versionchanged:: 5.0

               Previously, this method would set this `IOLoop` as the
               global singleton used by `IOLoop.instance()`. Now that
               `instance()` is an alias for `current()`, `install()`
               is an alias for `make_current()`.

            .. deprecated:: 5.0
            """
            self.make_current()

        @staticmethod
        def clear_instance() -> None:
            """Deprecated alias for `clear_current()`.

            .. versionchanged:: 5.0

               Previously, this method would clear the `IOLoop` used as
               the global singleton by `IOLoop.instance()`. Now that
               `instance()` is an alias for `current()`,
               `clear_instance()` is an alias for `clear_current()`.

            .. deprecated:: 5.0

            """
            IOLoop.clear_current()

        @typing.overload
        @staticmethod
        def current() -> "IOLoop":
            pass

        @typing.overload
        @staticmethod
        def current(instance: bool = True) -> Optional["IOLoop"]:  # noqa: F811
            pass

        @staticmethod
        def current(instance: bool = True) -> Optional["IOLoop"]:  # noqa: F811
            """Returns the current thread's `IOLoop`.

            If an `IOLoop` is currently running or has been marked as
            current by `make_current`, returns that instance.  If there is
            no current `IOLoop` and ``instance`` is true, creates one.

            .. versionchanged:: 4.1
               Added ``instance`` argument to control the fallback to
               `IOLoop.instance()`.
            .. versionchanged:: 5.0
               On Python 3, control of the current `IOLoop` is delegated
               to `asyncio`, with this and other methods as pass-through accessors.
               The ``instance`` argument now controls whether an `IOLoop`
               is created automatically when there is none, instead of
               whether we fall back to `IOLoop.instance()` (which is now
               an alias for this method). ``instance=False`` is deprecated,
               since even if we do not create an `IOLoop`, this method
               may initialize the asyncio loop.
            """
            try:
                loop = asyncio.get_event_loop()
            except (RuntimeError, AssertionError):
                if not instance:
                    return None
                raise
            try:
                return IOLoop._ioloop_for_asyncio[loop]
            except KeyError:
                if instance:
                    from tornado.platform.asyncio import AsyncIOMainLoop

                    current = AsyncIOMainLoop(make_current=True)  # type: Optional[IOLoop]
                else:
                    current = None
            return current

        def make_current(self) -> None:
            """Makes this the `IOLoop` for the current thread.

            An `IOLoop` automatically becomes current for its thread
            when it is started, but it is sometimes useful to call
            `make_current` explicitly before starting the `IOLoop`,
            so that code run at startup time can find the right
            instance.

            .. versionchanged:: 4.1
               An `IOLoop` created while there is no current `IOLoop`
               will automatically become current.

            .. versionchanged:: 5.0
               This method also sets the current `asyncio` event loop.
            """
            # The asyncio event loops override this method.
            raise NotImplementedError()

        @staticmethod
        def clear_current() -> None:
            """Clears the `IOLoop` for the current thread.

            Intended primarily for use by test frameworks in between tests.

            .. versionchanged:: 5.0
               This method also clears the current `asyncio` event loop.
            """
            old = IOLoop.current(instance=False)
            if old is not None:
                old._clear_current_hook()
            if asyncio is None:
                IOLoop._current.instance = None

        def _clear_current_hook(self) -> None:
            """Instance method called when an IOLoop ceases to be current.

            May be overridden by subclasses as a counterpart to make_current.
            """
            pass

        @classmethod
        def configurable_base(cls) -> Type[Configurable]:
            return IOLoop

        @classmethod
        def configurable_default(cls) -> Type[Configurable]:
            from tornado.platform.asyncio import AsyncIOLoop

            return AsyncIOLoop

        def initialize(self, make_current: Optional[bool] = None) -> None:
            if make_current is None:
                if IOLoop.current(instance=False) is None:
                    self.make_current()
            elif make_current:
                current = IOLoop.current(instance=False)
                # AsyncIO loops can already be current by this point.
                if current is not None and current is not self:
                    raise RuntimeError("current IOLoop already exists")
                self.make_current()

        def close(self, all_fds: bool = False) -> None:
            """Closes the `IOLoop`, freeing any resources used.

            If ``all_fds`` is true, all file descriptors registered on the
            IOLoop will be closed (not just the ones created by the
            `IOLoop` itself).

            Many applications will only use a single `IOLoop` that runs for the
            entire lifetime of the process.  In that case closing the `IOLoop`
            is not necessary since everything will be cleaned up when the
            process exits.  `IOLoop.close` is provided mainly for scenarios
            such as unit tests, which create and destroy a large number of
            ``IOLoops``.

            An `IOLoop` must be completely stopped before it can be closed.  This
            means that `IOLoop.stop()` must be called *and* `IOLoop.start()` must
            be allowed to return before attempting to call `IOLoop.close()`.
            Therefore the call to `close` will usually appear just after
            the call to `start` rather than near the call to `stop`.

            .. versionchanged:: 3.1
               If the `IOLoop` implementation supports non-integer objects
               for "file descriptors", those objects will have their
               ``close`` method when ``all_fds`` is true.
            """
            raise NotImplementedError()

        @typing.overload
        def add_handler(
            self, fd: int, handler: Callable[[int, int], None], events: int
        ) -> None:
            pass

        @typing.overload  # noqa: F811
        def add_handler(
            self, fd: _S, handler: Callable[[_S, int], None], events: int
        ) -> None:
            pass

        def add_handler(  # noqa: F811
            self, fd: Union[int, _Selectable], handler: Callable[..., None], events: int
        ) -> None:
            """Registers the given handler to receive the given events for ``fd``.

            The ``fd`` argument may either be an integer file descriptor or
            a file-like object with a ``fileno()`` and ``close()`` method.

            The ``events`` argument is a bitwise or of the constants
            ``IOLoop.READ``, ``IOLoop.WRITE``, and ``IOLoop.ERROR``.

            When an event occurs, ``handler(fd, events)`` will be run.

            .. versionchanged:: 4.0
               Added the ability to pass file-like objects in addition to
               raw file descriptors.
            """
            raise NotImplementedError()

        def update_handler(self, fd: Union[int, _Selectable], events: int) -> None:
            """Changes the events we listen for ``fd``.

            .. versionchanged:: 4.0
               Added the ability to pass file-like objects in addition to
               raw file descriptors.
            """
            raise NotImplementedError()

        def remove_handler(self, fd: Union[int, _Selectable]) -> None:
            """Stop listening for events on ``fd``.

            .. versionchanged:: 4.0
               Added the ability to pass file-like objects in addition to
               raw file descriptors.
            """
            raise NotImplementedError()

        def start(self) -> None:
            """Starts the I/O loop.

            The loop will run until one of the callbacks calls `stop()`, which
            will make the loop stop after the current event iteration completes.
            """
            raise NotImplementedError()

        def _setup_logging(self) -> None:
            """The IOLoop catches and logs exceptions, so it's
            important that log output be visible.  However, python's
            default behavior for non-root loggers (prior to python
            3.2) is to print an unhelpful "no handlers could be
            found" message rather than the actual log entry, so we
            must explicitly configure logging if we've made it this
            far without anything.

            This method should be called from start() in subclasses.
            """
            if not any(
                [
                    logging.getLogger().handlers,
                    logging.getLogger("tornado").handlers,
                    logging.getLogger("tornado.application").handlers,
                ]
            ):
                logging.basicConfig()

        def stop(self) -> None:
            """Stop the I/O loop.

            If the event loop is not currently running, the next call to `start()`
            will return immediately.

            Note that even after `stop` has been called, the `IOLoop` is not
            completely stopped until `IOLoop.start` has also returned.
            Some work that was scheduled before the call to `stop` may still
            be run before the `IOLoop` shuts down.
            """
            raise NotImplementedError()

        def run_sync(self, func: Callable, timeout: Optional[float] = None) -> Any:
            """Starts the `IOLoop`, runs the given function, and stops the loop.

            The function must return either an awaitable object or
            ``None``. If the function returns an awaitable object, the
            `IOLoop` will run until the awaitable is resolved (and
            `run_sync()` will return the awaitable's result). If it raises
            an exception, the `IOLoop` will stop and the exception will be
            re-raised to the caller.

            The keyword-only argument ``timeout`` may be used to set
            a maximum duration for the function.  If the timeout expires,
            a `tornado.util.TimeoutError` is raised.

            This method is useful to allow asynchronous calls in a
            ``main()`` function::

                async def main():
                    # do stuff...

                if __name__ == '__main__':
                    IOLoop.current().run_sync(main)

            .. versionchanged:: 4.3
               Returning a non-``None``, non-awaitable value is now an error.

            .. versionchanged:: 5.0
               If a timeout occurs, the ``func`` coroutine will be cancelled.

            """
            future_cell = [None]  # type: List[Optional[Future]]

            def run() -> None:
                try:
                    result = func()
                    if result is not None:
                        from tornado.gen import convert_yielded

                        result = convert_yielded(result)
                except Exception:
                    fut = Future()  # type: Future[Any]
                    future_cell[0] = fut
                    future_set_exc_info(fut, sys.exc_info())
                else:
                    if is_future(result):
                        future_cell[0] = result
                    else:
                        fut = Future()
                        future_cell[0] = fut
                        fut.set_result(result)
                assert future_cell[0] is not None
                self.add_future(future_cell[0], lambda future: self.stop())

            self.add_callback(run)
            if timeout is not None:

                def timeout_callback() -> None:
                    # If we can cancel the future, do so and wait on it. If not,
                    # Just stop the loop and return with the task still pending.
                    # (If we neither cancel nor wait for the task, a warning
                    # will be logged).
                    assert future_cell[0] is not None
                    if not future_cell[0].cancel():
                        self.stop()

                timeout_handle = self.add_timeout(self.time() + timeout, timeout_callback)
            self.start()
            if timeout is not None:
                self.remove_timeout(timeout_handle)
            assert future_cell[0] is not None
            if future_cell[0].cancelled() or not future_cell[0].done():
                raise TimeoutError("Operation timed out after %s seconds" % timeout)
            return future_cell[0].result()

        def time(self) -> float:
            """Returns the current time according to the `IOLoop`'s clock.

            The return value is a floating-point number relative to an
            unspecified time in the past.

            Historically, the IOLoop could be customized to use e.g.
            `time.monotonic` instead of `time.time`, but this is not
            currently supported and so this method is equivalent to
            `time.time`.

            """
            return time.time()

        def add_timeout(
            self,
            deadline: Union[float, datetime.timedelta],
            callback: Callable[..., None],
            *args: Any,
            **kwargs: Any
        ) -> object:
            """Runs the ``callback`` at the time ``deadline`` from the I/O loop.

            Returns an opaque handle that may be passed to
            `remove_timeout` to cancel.

            ``deadline`` may be a number denoting a time (on the same
            scale as `IOLoop.time`, normally `time.time`), or a
            `datetime.timedelta` object for a deadline relative to the
            current time.  Since Tornado 4.0, `call_later` is a more
            convenient alternative for the relative case since it does not
            require a timedelta object.

            Note that it is not safe to call `add_timeout` from other threads.
            Instead, you must use `add_callback` to transfer control to the
            `IOLoop`'s thread, and then call `add_timeout` from there.

            Subclasses of IOLoop must implement either `add_timeout` or
            `call_at`; the default implementations of each will call
            the other.  `call_at` is usually easier to implement, but
            subclasses that wish to maintain compatibility with Tornado
            versions prior to 4.0 must use `add_timeout` instead.

            .. versionchanged:: 4.0
               Now passes through ``*args`` and ``**kwargs`` to the callback.
            """
            if isinstance(deadline, numbers.Real):
                return self.call_at(deadline, callback, *args, **kwargs)
            elif isinstance(deadline, datetime.timedelta):
                return self.call_at(
                    self.time() + deadline.total_seconds(), callback, *args, **kwargs
                )
            else:
                raise TypeError("Unsupported deadline %r" % deadline)

        def call_later(
            self, delay: float, callback: Callable[..., None], *args: Any, **kwargs: Any
        ) -> object:
            """Runs the ``callback`` after ``delay`` seconds have passed.

            Returns an opaque handle that may be passed to `remove_timeout`
            to cancel.  Note that unlike the `asyncio` method of the same
            name, the returned object does not have a ``cancel()`` method.

            See `add_timeout` for comments on thread-safety and subclassing.

            .. versionadded:: 4.0
            """
            return self.call_at(self.time() + delay, callback, *args, **kwargs)

        def call_at(
            self, when: float, callback: Callable[..., None], *args: Any, **kwargs: Any
        ) -> object:
            """Runs the ``callback`` at the absolute time designated by ``when``.

            ``when`` must be a number using the same reference point as
            `IOLoop.time`.

            Returns an opaque handle that may be passed to `remove_timeout`
            to cancel.  Note that unlike the `asyncio` method of the same
            name, the returned object does not have a ``cancel()`` method.

            See `add_timeout` for comments on thread-safety and subclassing.

            .. versionadded:: 4.0
            """
            return self.add_timeout(when, callback, *args, **kwargs)

        def remove_timeout(self, timeout: object) -> None:
            """Cancels a pending timeout.

            The argument is a handle as returned by `add_timeout`.  It is
            safe to call `remove_timeout` even if the callback has already
            been run.
            """
            raise NotImplementedError()

        def add_callback(self, callback: Callable, *args: Any, **kwargs: Any) -> None:
            """Calls the given callback on the next I/O loop iteration.

            It is safe to call this method from any thread at any time,
            except from a signal handler.  Note that this is the **only**
            method in `IOLoop` that makes this thread-safety guarantee; all
            other interaction with the `IOLoop` must be done from that
            `IOLoop`'s thread.  `add_callback()` may be used to transfer
            control from other threads to the `IOLoop`'s thread.

            To add a callback from a signal handler, see
            `add_callback_from_signal`.
            """
            raise NotImplementedError()

        def add_callback_from_signal(
            self, callback: Callable, *args: Any, **kwargs: Any
        ) -> None:
            """Calls the given callback on the next I/O loop iteration.

            Safe for use from a Python signal handler; should not be used
            otherwise.
            """
            raise NotImplementedError()

        def spawn_callback(self, callback: Callable, *args: Any, **kwargs: Any) -> None:
            """Calls the given callback on the next IOLoop iteration.

            As of Tornado 6.0, this method is equivalent to `add_callback`.

            .. versionadded:: 4.0
            """
            self.add_callback(callback, *args, **kwargs)

        def add_future(
            self,
            future: "Union[Future[_T], concurrent.futures.Future[_T]]",
            callback: Callable[["Future[_T]"], None],
        ) -> None:
            """Schedules a callback on the ``IOLoop`` when the given
            `.Future` is finished.

            The callback is invoked with one argument, the
            `.Future`.

            This method only accepts `.Future` objects and not other
            awaitables (unlike most of Tornado where the two are
            interchangeable).
            """
            if isinstance(future, Future):
                # Note that we specifically do not want the inline behavior of
                # tornado.concurrent.future_add_done_callback. We always want
                # this callback scheduled on the next IOLoop iteration (which
                # asyncio.Future always does).
                #
                # Wrap the callback in self._run_callback so we control
                # the error logging (i.e. it goes to tornado.log.app_log
                # instead of asyncio's log).
                future.add_done_callback(
                    lambda f: self._run_callback(functools.partial(callback, future))
                )
            else:
                assert is_future(future)
                # For concurrent futures, we use self.add_callback, so
                # it's fine if future_add_done_callback inlines that call.
                future_add_done_callback(
                    future, lambda f: self.add_callback(callback, future)
                )

        def run_in_executor(
            self,
            executor: Optional[concurrent.futures.Executor],
            func: Callable[..., _T],
            *args: Any
        ) -> Awaitable[_T]:
            """Runs a function in a ``concurrent.futures.Executor``. If
            ``executor`` is ``None``, the IO loop's default executor will be used.

            Use `functools.partial` to pass keyword arguments to ``func``.

            .. versionadded:: 5.0
            """
            if executor is None:
                if not hasattr(self, "_executor"):
                    from tornado.process import cpu_count

                    self._executor = concurrent.futures.ThreadPoolExecutor(
                        max_workers=(cpu_count() * 5)
                    )  # type: concurrent.futures.Executor
                executor = self._executor
            c_future = executor.submit(func, *args)
            # Concurrent Futures are not usable with await. Wrap this in a
            # Tornado Future instead, using self.add_future for thread-safety.
            t_future = Future()  # type: Future[_T]
            self.add_future(c_future, lambda f: chain_future(f, t_future))
            return t_future

        def set_default_executor(self, executor: concurrent.futures.Executor) -> None:
            """Sets the default executor to use with :meth:`run_in_executor`.

            .. versionadded:: 5.0
            """
            self._executor = executor

        def _run_callback(self, callback: Callable[[], Any]) -> None:
            """Runs a callback with error handling.

            .. versionchanged:: 6.0

               CancelledErrors are no longer logged.
            """
            try:
                ret = callback()
                if ret is not None:
                    from tornado import gen

                    # Functions that return Futures typically swallow all
                    # exceptions and store them in the Future.  If a Future
                    # makes it out to the IOLoop, ensure its exception (if any)
                    # gets logged too.
                    try:
                        ret = gen.convert_yielded(ret)
                    except gen.BadYieldError:
                        # It's not unusual for add_callback to be used with
                        # methods returning a non-None and non-yieldable
                        # result, which should just be ignored.
                        pass
                    else:
                        self.add_future(ret, self._discard_future_result)
            except asyncio.CancelledError:
                pass
            except Exception:
                app_log.error("Exception in callback %r", callback, exc_info=True)

        def _discard_future_result(self, future: Future) -> None:
            """Avoid unhandled-exception warnings from spawned coroutines."""
            future.result()

        def split_fd(
            self, fd: Union[int, _Selectable]
        ) -> Tuple[int, Union[int, _Selectable]]:
            # """Returns an (fd, obj) pair from an ``fd`` parameter.

            # We accept both raw file descriptors and file-like objects as
            # input to `add_handler` and related methods.  When a file-like
            # object is passed, we must retain the object itself so we can
            # close it correctly when the `IOLoop` shuts down, but the
            # poller interfaces favor file descriptors (they will accept
            # file-like objects and call ``fileno()`` for you, but they
            # always return the descriptor itself).

            # This method is provided for use by `IOLoop` subclasses and should
            # not generally be used by application code.

            # .. versionadded:: 4.0
            # """
            if isinstance(fd, int):
                return fd, fd
            return fd.fileno(), fd

        def close_fd(self, fd: Union[int, _Selectable]) -> None:
            # """Utility method to close an ``fd``.

            # If ``fd`` is a file-like object, we close it directly; otherwise
            # we use `os.close`.

            # This method is provided for use by `IOLoop` subclasses (in
            # implementations of ``IOLoop.close(all_fds=True)`` and should
            # not generally be used by application code.

            # .. versionadded:: 4.0
            # """
            try:
                if isinstance(fd, int):
                    os.close(fd)
                else:
                    fd.close()
            except OSError:
                pass

    class _Timeout(object):
        """An IOLoop timeout, a UNIX timestamp and a callback"""

        # Reduce memory overhead when there are lots of pending callbacks
        __slots__ = ["deadline", "callback", "tdeadline"]

        def __init__(
            self, deadline: float, callback: Callable[[], None], io_loop: IOLoop
        ) -> None:
            if not isinstance(deadline, numbers.Real):
                raise TypeError("Unsupported deadline %r" % deadline)
            self.deadline = deadline
            self.callback = callback
            self.tdeadline = (
                deadline,
                next(io_loop._timeout_counter),
            )  # type: Tuple[float, int]

        # Comparison methods to sort by deadline, with object id as a tiebreaker
        # to guarantee a consistent ordering.  The heapq module uses __le__
        # in python2.5, and __lt__ in 2.6+ (sort() and most other comparisons
        # use __lt__).
        def __lt__(self, other: "_Timeout") -> bool:
            return self.tdeadline < other.tdeadline

        def __le__(self, other: "_Timeout") -> bool:
            return self.tdeadline <= other.tdeadline

    class PeriodicCallback(object):
        """Schedules the given callback to be called periodically.

        The callback is called every ``callback_time`` milliseconds.
        Note that the timeout is given in milliseconds, while most other
        time-related functions in Tornado use seconds.

        If ``jitter`` is specified, each callback time will be randomly selected
        within a window of ``jitter * callback_time`` milliseconds.
        Jitter can be used to reduce alignment of events with similar periods.
        A jitter of 0.1 means allowing a 10% variation in callback time.
        The window is centered on ``callback_time`` so the total number of calls
        within a given interval should not be significantly affected by adding
        jitter.

        If the callback runs for longer than ``callback_time`` milliseconds,
        subsequent invocations will be skipped to get back on schedule.

        `start` must be called after the `PeriodicCallback` is created.

        .. versionchanged:: 5.0
           The ``io_loop`` argument (deprecated since version 4.1) has been removed.

        .. versionchanged:: 5.1
           The ``jitter`` argument is added.
        """

        def __init__(
            self, callback: Callable[[], None], callback_time: float, jitter: float = 0
        ) -> None:
            self.callback = callback
            if callback_time <= 0:
                raise ValueError("Periodic callback must have a positive callback_time")
            self.callback_time = callback_time
            self.jitter = jitter
            self._running = False
            self._timeout = None  # type: object

        def start(self) -> None:
            """Starts the timer."""
            # Looking up the IOLoop here allows to first instantiate the
            # PeriodicCallback in another thread, then start it using
            # IOLoop.add_callback().
            self.io_loop = IOLoop.current()
            self._running = True
            self._next_timeout = self.io_loop.time()
            self._schedule_next()

        def stop(self) -> None:
            """Stops the timer."""
            self._running = False
            if self._timeout is not None:
                self.io_loop.remove_timeout(self._timeout)
                self._timeout = None

        def is_running(self) -> bool:
            """Returns ``True`` if this `.PeriodicCallback` has been started.

            .. versionadded:: 4.1
            """
            return self._running

        def _run(self) -> None:
            if not self._running:
                return
            try:
                return self.callback()
            except Exception:
                app_log.error("Exception in callback %r", self.callback, exc_info=True)
            finally:
                self._schedule_next()

        def _schedule_next(self) -> None:
            if self._running:
                self._update_next(self.io_loop.time())
                self._timeout = self.io_loop.add_timeout(self._next_timeout, self._run)

        def _update_next(self, current_time: float) -> None:
            callback_time_sec = self.callback_time / 1000.0
            if self.jitter:
                # apply jitter fraction
                callback_time_sec *= 1 + (self.jitter * (random.random() - 0.5))
            if self._next_timeout <= current_time:
                # The period should be measured from the start of one call
                # to the start of the next. If one call takes too long,
                # skip cycles to get back to a multiple of the original
                # schedule.
                self._next_timeout += (
                    math.floor((current_time - self._next_timeout) / callback_time_sec) + 1
                ) * callback_time_sec
            else:
                # If the clock moved backwards, ensure we advance the next
                # timeout instead of recomputing the same value again.
                # This may result in long gaps between callbacks if the
                # clock jumps backwards by a lot, but the far more common
                # scenario is a small NTP adjustment that should just be
                # ignored.
                #
                # Note that on some systems if time.time() runs slower
                # than time.monotonic() (most common on windows), we
                # effectively experience a small backwards time jump on
                # every iteration because PeriodicCallback uses
                # time.time() while asyncio schedules callbacks using
                # time.monotonic().
                # https://github.com/tornadoweb/tornado/issues/2333
                self._next_timeout += callback_time_sec