add ydb deps

5 files changed, 1789 insertions, 0 deletions

diff --git a/contrib/tools/python3/src/Lib/concurrent/__init__.py b/contrib/tools/python3/src/Lib/concurrent/__init__.py
new file mode 100644
index 0000000000..196d378857
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/concurrent/__init__.py
@@ -0,0 +1 @@
+# This directory is a Python package.
diff --git a/contrib/tools/python3/src/Lib/concurrent/futures/__init__.py b/contrib/tools/python3/src/Lib/concurrent/futures/__init__.py
new file mode 100644
index 0000000000..292e886d5a
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/concurrent/futures/__init__.py
@@ -0,0 +1,53 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Execute computations asynchronously using threads or processes."""
+
+__author__ = 'Brian Quinlan (brian@sweetapp.com)'
+
+from concurrent.futures._base import (FIRST_COMPLETED,
+                                      FIRST_EXCEPTION,
+                                      ALL_COMPLETED,
+                                      CancelledError,
+                                      TimeoutError,
+                                      InvalidStateError,
+                                      BrokenExecutor,
+                                      Future,
+                                      Executor,
+                                      wait,
+                                      as_completed)
+
+__all__ = (
+    'FIRST_COMPLETED',
+    'FIRST_EXCEPTION',
+    'ALL_COMPLETED',
+    'CancelledError',
+    'TimeoutError',
+    'BrokenExecutor',
+    'Future',
+    'Executor',
+    'wait',
+    'as_completed',
+    'ProcessPoolExecutor',
+    'ThreadPoolExecutor',
+)
+
+
+def __dir__():
+    return __all__ + ('__author__', '__doc__')
+
+
+def __getattr__(name):
+    global ProcessPoolExecutor, ThreadPoolExecutor
+
+    if name == 'ProcessPoolExecutor':
+        from .process import ProcessPoolExecutor as pe
+        ProcessPoolExecutor = pe
+        return pe
+
+    if name == 'ThreadPoolExecutor':
+        from .thread import ThreadPoolExecutor as te
+        ThreadPoolExecutor = te
+        return te
+
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/contrib/tools/python3/src/Lib/concurrent/futures/_base.py b/contrib/tools/python3/src/Lib/concurrent/futures/_base.py
new file mode 100644
index 0000000000..6742a07753
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/concurrent/futures/_base.py
@@ -0,0 +1,654 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+__author__ = 'Brian Quinlan (brian@sweetapp.com)'
+
+import collections
+import logging
+import threading
+import time
+import types
+
+FIRST_COMPLETED = 'FIRST_COMPLETED'
+FIRST_EXCEPTION = 'FIRST_EXCEPTION'
+ALL_COMPLETED = 'ALL_COMPLETED'
+_AS_COMPLETED = '_AS_COMPLETED'
+
+# Possible future states (for internal use by the futures package).
+PENDING = 'PENDING'
+RUNNING = 'RUNNING'
+# The future was cancelled by the user...
+CANCELLED = 'CANCELLED'
+# ...and _Waiter.add_cancelled() was called by a worker.
+CANCELLED_AND_NOTIFIED = 'CANCELLED_AND_NOTIFIED'
+FINISHED = 'FINISHED'
+
+_FUTURE_STATES = [
+    PENDING,
+    RUNNING,
+    CANCELLED,
+    CANCELLED_AND_NOTIFIED,
+    FINISHED
+]
+
+_STATE_TO_DESCRIPTION_MAP = {
+    PENDING: "pending",
+    RUNNING: "running",
+    CANCELLED: "cancelled",
+    CANCELLED_AND_NOTIFIED: "cancelled",
+    FINISHED: "finished"
+}
+
+# Logger for internal use by the futures package.
+LOGGER = logging.getLogger("concurrent.futures")
+
+class Error(Exception):
+    """Base class for all future-related exceptions."""
+    pass
+
+class CancelledError(Error):
+    """The Future was cancelled."""
+    pass
+
+TimeoutError = TimeoutError  # make local alias for the standard exception
+
+class InvalidStateError(Error):
+    """The operation is not allowed in this state."""
+    pass
+
+class _Waiter(object):
+    """Provides the event that wait() and as_completed() block on."""
+    def __init__(self):
+        self.event = threading.Event()
+        self.finished_futures = []
+
+    def add_result(self, future):
+        self.finished_futures.append(future)
+
+    def add_exception(self, future):
+        self.finished_futures.append(future)
+
+    def add_cancelled(self, future):
+        self.finished_futures.append(future)
+
+class _AsCompletedWaiter(_Waiter):
+    """Used by as_completed()."""
+
+    def __init__(self):
+        super(_AsCompletedWaiter, self).__init__()
+        self.lock = threading.Lock()
+
+    def add_result(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_result(future)
+            self.event.set()
+
+    def add_exception(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_exception(future)
+            self.event.set()
+
+    def add_cancelled(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_cancelled(future)
+            self.event.set()
+
+class _FirstCompletedWaiter(_Waiter):
+    """Used by wait(return_when=FIRST_COMPLETED)."""
+
+    def add_result(self, future):
+        super().add_result(future)
+        self.event.set()
+
+    def add_exception(self, future):
+        super().add_exception(future)
+        self.event.set()
+
+    def add_cancelled(self, future):
+        super().add_cancelled(future)
+        self.event.set()
+
+class _AllCompletedWaiter(_Waiter):
+    """Used by wait(return_when=FIRST_EXCEPTION and ALL_COMPLETED)."""
+
+    def __init__(self, num_pending_calls, stop_on_exception):
+        self.num_pending_calls = num_pending_calls
+        self.stop_on_exception = stop_on_exception
+        self.lock = threading.Lock()
+        super().__init__()
+
+    def _decrement_pending_calls(self):
+        with self.lock:
+            self.num_pending_calls -= 1
+            if not self.num_pending_calls:
+                self.event.set()
+
+    def add_result(self, future):
+        super().add_result(future)
+        self._decrement_pending_calls()
+
+    def add_exception(self, future):
+        super().add_exception(future)
+        if self.stop_on_exception:
+            self.event.set()
+        else:
+            self._decrement_pending_calls()
+
+    def add_cancelled(self, future):
+        super().add_cancelled(future)
+        self._decrement_pending_calls()
+
+class _AcquireFutures(object):
+    """A context manager that does an ordered acquire of Future conditions."""
+
+    def __init__(self, futures):
+        self.futures = sorted(futures, key=id)
+
+    def __enter__(self):
+        for future in self.futures:
+            future._condition.acquire()
+
+    def __exit__(self, *args):
+        for future in self.futures:
+            future._condition.release()
+
+def _create_and_install_waiters(fs, return_when):
+    if return_when == _AS_COMPLETED:
+        waiter = _AsCompletedWaiter()
+    elif return_when == FIRST_COMPLETED:
+        waiter = _FirstCompletedWaiter()
+    else:
+        pending_count = sum(
+                f._state not in [CANCELLED_AND_NOTIFIED, FINISHED] for f in fs)
+
+        if return_when == FIRST_EXCEPTION:
+            waiter = _AllCompletedWaiter(pending_count, stop_on_exception=True)
+        elif return_when == ALL_COMPLETED:
+            waiter = _AllCompletedWaiter(pending_count, stop_on_exception=False)
+        else:
+            raise ValueError("Invalid return condition: %r" % return_when)
+
+    for f in fs:
+        f._waiters.append(waiter)
+
+    return waiter
+
+
+def _yield_finished_futures(fs, waiter, ref_collect):
+    """
+    Iterate on the list *fs*, yielding finished futures one by one in
+    reverse order.
+    Before yielding a future, *waiter* is removed from its waiters
+    and the future is removed from each set in the collection of sets
+    *ref_collect*.
+
+    The aim of this function is to avoid keeping stale references after
+    the future is yielded and before the iterator resumes.
+    """
+    while fs:
+        f = fs[-1]
+        for futures_set in ref_collect:
+            futures_set.remove(f)
+        with f._condition:
+            f._waiters.remove(waiter)
+        del f
+        # Careful not to keep a reference to the popped value
+        yield fs.pop()
+
+
+def as_completed(fs, timeout=None):
+    """An iterator over the given futures that yields each as it completes.
+
+    Args:
+        fs: The sequence of Futures (possibly created by different Executors) to
+            iterate over.
+        timeout: The maximum number of seconds to wait. If None, then there
+            is no limit on the wait time.
+
+    Returns:
+        An iterator that yields the given Futures as they complete (finished or
+        cancelled). If any given Futures are duplicated, they will be returned
+        once.
+
+    Raises:
+        TimeoutError: If the entire result iterator could not be generated
+            before the given timeout.
+    """
+    if timeout is not None:
+        end_time = timeout + time.monotonic()
+
+    fs = set(fs)
+    total_futures = len(fs)
+    with _AcquireFutures(fs):
+        finished = set(
+                f for f in fs
+                if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])
+        pending = fs - finished
+        waiter = _create_and_install_waiters(fs, _AS_COMPLETED)
+    finished = list(finished)
+    try:
+        yield from _yield_finished_futures(finished, waiter,
+                                           ref_collect=(fs,))
+
+        while pending:
+            if timeout is None:
+                wait_timeout = None
+            else:
+                wait_timeout = end_time - time.monotonic()
+                if wait_timeout < 0:
+                    raise TimeoutError(
+                            '%d (of %d) futures unfinished' % (
+                            len(pending), total_futures))
+
+            waiter.event.wait(wait_timeout)
+
+            with waiter.lock:
+                finished = waiter.finished_futures
+                waiter.finished_futures = []
+                waiter.event.clear()
+
+            # reverse to keep finishing order
+            finished.reverse()
+            yield from _yield_finished_futures(finished, waiter,
+                                               ref_collect=(fs, pending))
+
+    finally:
+        # Remove waiter from unfinished futures
+        for f in fs:
+            with f._condition:
+                f._waiters.remove(waiter)
+
+DoneAndNotDoneFutures = collections.namedtuple(
+        'DoneAndNotDoneFutures', 'done not_done')
+def wait(fs, timeout=None, return_when=ALL_COMPLETED):
+    """Wait for the futures in the given sequence to complete.
+
+    Args:
+        fs: The sequence of Futures (possibly created by different Executors) to
+            wait upon.
+        timeout: The maximum number of seconds to wait. If None, then there
+            is no limit on the wait time.
+        return_when: Indicates when this function should return. The options
+            are:
+
+            FIRST_COMPLETED - Return when any future finishes or is
+                              cancelled.
+            FIRST_EXCEPTION - Return when any future finishes by raising an
+                              exception. If no future raises an exception
+                              then it is equivalent to ALL_COMPLETED.
+            ALL_COMPLETED -   Return when all futures finish or are cancelled.
+
+    Returns:
+        A named 2-tuple of sets. The first set, named 'done', contains the
+        futures that completed (is finished or cancelled) before the wait
+        completed. The second set, named 'not_done', contains uncompleted
+        futures. Duplicate futures given to *fs* are removed and will be
+        returned only once.
+    """
+    fs = set(fs)
+    with _AcquireFutures(fs):
+        done = {f for f in fs
+                   if f._state in [CANCELLED_AND_NOTIFIED, FINISHED]}
+        not_done = fs - done
+        if (return_when == FIRST_COMPLETED) and done:
+            return DoneAndNotDoneFutures(done, not_done)
+        elif (return_when == FIRST_EXCEPTION) and done:
+            if any(f for f in done
+                   if not f.cancelled() and f.exception() is not None):
+                return DoneAndNotDoneFutures(done, not_done)
+
+        if len(done) == len(fs):
+            return DoneAndNotDoneFutures(done, not_done)
+
+        waiter = _create_and_install_waiters(fs, return_when)
+
+    waiter.event.wait(timeout)
+    for f in fs:
+        with f._condition:
+            f._waiters.remove(waiter)
+
+    done.update(waiter.finished_futures)
+    return DoneAndNotDoneFutures(done, fs - done)
+
+
+def _result_or_cancel(fut, timeout=None):
+    try:
+        try:
+            return fut.result(timeout)
+        finally:
+            fut.cancel()
+    finally:
+        # Break a reference cycle with the exception in self._exception
+        del fut
+
+
+class Future(object):
+    """Represents the result of an asynchronous computation."""
+
+    def __init__(self):
+        """Initializes the future. Should not be called by clients."""
+        self._condition = threading.Condition()
+        self._state = PENDING
+        self._result = None
+        self._exception = None
+        self._waiters = []
+        self._done_callbacks = []
+
+    def _invoke_callbacks(self):
+        for callback in self._done_callbacks:
+            try:
+                callback(self)
+            except Exception:
+                LOGGER.exception('exception calling callback for %r', self)
+
+    def __repr__(self):
+        with self._condition:
+            if self._state == FINISHED:
+                if self._exception:
+                    return '<%s at %#x state=%s raised %s>' % (
+                        self.__class__.__name__,
+                        id(self),
+                        _STATE_TO_DESCRIPTION_MAP[self._state],
+                        self._exception.__class__.__name__)
+                else:
+                    return '<%s at %#x state=%s returned %s>' % (
+                        self.__class__.__name__,
+                        id(self),
+                        _STATE_TO_DESCRIPTION_MAP[self._state],
+                        self._result.__class__.__name__)
+            return '<%s at %#x state=%s>' % (
+                    self.__class__.__name__,
+                    id(self),
+                   _STATE_TO_DESCRIPTION_MAP[self._state])
+
+    def cancel(self):
+        """Cancel the future if possible.
+
+        Returns True if the future was cancelled, False otherwise. A future
+        cannot be cancelled if it is running or has already completed.
+        """
+        with self._condition:
+            if self._state in [RUNNING, FINISHED]:
+                return False
+
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                return True
+
+            self._state = CANCELLED
+            self._condition.notify_all()
+
+        self._invoke_callbacks()
+        return True
+
+    def cancelled(self):
+        """Return True if the future was cancelled."""
+        with self._condition:
+            return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]
+
+    def running(self):
+        """Return True if the future is currently executing."""
+        with self._condition:
+            return self._state == RUNNING
+
+    def done(self):
+        """Return True if the future was cancelled or finished executing."""
+        with self._condition:
+            return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]
+
+    def __get_result(self):
+        if self._exception:
+            try:
+                raise self._exception
+            finally:
+                # Break a reference cycle with the exception in self._exception
+                self = None
+        else:
+            return self._result
+
+    def add_done_callback(self, fn):
+        """Attaches a callable that will be called when the future finishes.
+
+        Args:
+            fn: A callable that will be called with this future as its only
+                argument when the future completes or is cancelled. The callable
+                will always be called by a thread in the same process in which
+                it was added. If the future has already completed or been
+                cancelled then the callable will be called immediately. These
+                callables are called in the order that they were added.
+        """
+        with self._condition:
+            if self._state not in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]:
+                self._done_callbacks.append(fn)
+                return
+        try:
+            fn(self)
+        except Exception:
+            LOGGER.exception('exception calling callback for %r', self)
+
+    def result(self, timeout=None):
+        """Return the result of the call that the future represents.
+
+        Args:
+            timeout: The number of seconds to wait for the result if the future
+                isn't done. If None, then there is no limit on the wait time.
+
+        Returns:
+            The result of the call that the future represents.
+
+        Raises:
+            CancelledError: If the future was cancelled.
+            TimeoutError: If the future didn't finish executing before the given
+                timeout.
+            Exception: If the call raised then that exception will be raised.
+        """
+        try:
+            with self._condition:
+                if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                    raise CancelledError()
+                elif self._state == FINISHED:
+                    return self.__get_result()
+
+                self._condition.wait(timeout)
+
+                if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                    raise CancelledError()
+                elif self._state == FINISHED:
+                    return self.__get_result()
+                else:
+                    raise TimeoutError()
+        finally:
+            # Break a reference cycle with the exception in self._exception
+            self = None
+
+    def exception(self, timeout=None):
+        """Return the exception raised by the call that the future represents.
+
+        Args:
+            timeout: The number of seconds to wait for the exception if the
+                future isn't done. If None, then there is no limit on the wait
+                time.
+
+        Returns:
+            The exception raised by the call that the future represents or None
+            if the call completed without raising.
+
+        Raises:
+            CancelledError: If the future was cancelled.
+            TimeoutError: If the future didn't finish executing before the given
+                timeout.
+        """
+
+        with self._condition:
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self._exception
+
+            self._condition.wait(timeout)
+
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self._exception
+            else:
+                raise TimeoutError()
+
+    # The following methods should only be used by Executors and in tests.
+    def set_running_or_notify_cancel(self):
+        """Mark the future as running or process any cancel notifications.
+
+        Should only be used by Executor implementations and unit tests.
+
+        If the future has been cancelled (cancel() was called and returned
+        True) then any threads waiting on the future completing (though calls
+        to as_completed() or wait()) are notified and False is returned.
+
+        If the future was not cancelled then it is put in the running state
+        (future calls to running() will return True) and True is returned.
+
+        This method should be called by Executor implementations before
+        executing the work associated with this future. If this method returns
+        False then the work should not be executed.
+
+        Returns:
+            False if the Future was cancelled, True otherwise.
+
+        Raises:
+            RuntimeError: if this method was already called or if set_result()
+                or set_exception() was called.
+        """
+        with self._condition:
+            if self._state == CANCELLED:
+                self._state = CANCELLED_AND_NOTIFIED
+                for waiter in self._waiters:
+                    waiter.add_cancelled(self)
+                # self._condition.notify_all() is not necessary because
+                # self.cancel() triggers a notification.
+                return False
+            elif self._state == PENDING:
+                self._state = RUNNING
+                return True
+            else:
+                LOGGER.critical('Future %s in unexpected state: %s',
+                                id(self),
+                                self._state)
+                raise RuntimeError('Future in unexpected state')
+
+    def set_result(self, result):
+        """Sets the return value of work associated with the future.
+
+        Should only be used by Executor implementations and unit tests.
+        """
+        with self._condition:
+            if self._state in {CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED}:
+                raise InvalidStateError('{}: {!r}'.format(self._state, self))
+            self._result = result
+            self._state = FINISHED
+            for waiter in self._waiters:
+                waiter.add_result(self)
+            self._condition.notify_all()
+        self._invoke_callbacks()
+
+    def set_exception(self, exception):
+        """Sets the result of the future as being the given exception.
+
+        Should only be used by Executor implementations and unit tests.
+        """
+        with self._condition:
+            if self._state in {CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED}:
+                raise InvalidStateError('{}: {!r}'.format(self._state, self))
+            self._exception = exception
+            self._state = FINISHED
+            for waiter in self._waiters:
+                waiter.add_exception(self)
+            self._condition.notify_all()
+        self._invoke_callbacks()
+
+    __class_getitem__ = classmethod(types.GenericAlias)
+
+class Executor(object):
+    """This is an abstract base class for concrete asynchronous executors."""
+
+    def submit(self, fn, /, *args, **kwargs):
+        """Submits a callable to be executed with the given arguments.
+
+        Schedules the callable to be executed as fn(*args, **kwargs) and returns
+        a Future instance representing the execution of the callable.
+
+        Returns:
+            A Future representing the given call.
+        """
+        raise NotImplementedError()
+
+    def map(self, fn, *iterables, timeout=None, chunksize=1):
+        """Returns an iterator equivalent to map(fn, iter).
+
+        Args:
+            fn: A callable that will take as many arguments as there are
+                passed iterables.
+            timeout: The maximum number of seconds to wait. If None, then there
+                is no limit on the wait time.
+            chunksize: The size of the chunks the iterable will be broken into
+                before being passed to a child process. This argument is only
+                used by ProcessPoolExecutor; it is ignored by
+                ThreadPoolExecutor.
+
+        Returns:
+            An iterator equivalent to: map(func, *iterables) but the calls may
+            be evaluated out-of-order.
+
+        Raises:
+            TimeoutError: If the entire result iterator could not be generated
+                before the given timeout.
+            Exception: If fn(*args) raises for any values.
+        """
+        if timeout is not None:
+            end_time = timeout + time.monotonic()
+
+        fs = [self.submit(fn, *args) for args in zip(*iterables)]
+
+        # Yield must be hidden in closure so that the futures are submitted
+        # before the first iterator value is required.
+        def result_iterator():
+            try:
+                # reverse to keep finishing order
+                fs.reverse()
+                while fs:
+                    # Careful not to keep a reference to the popped future
+                    if timeout is None:
+                        yield _result_or_cancel(fs.pop())
+                    else:
+                        yield _result_or_cancel(fs.pop(), end_time - time.monotonic())
+            finally:
+                for future in fs:
+                    future.cancel()
+        return result_iterator()
+
+    def shutdown(self, wait=True, *, cancel_futures=False):
+        """Clean-up the resources associated with the Executor.
+
+        It is safe to call this method several times. Otherwise, no other
+        methods can be called after this one.
+
+        Args:
+            wait: If True then shutdown will not return until all running
+                futures have finished executing and the resources used by the
+                executor have been reclaimed.
+            cancel_futures: If True then shutdown will cancel all pending
+                futures. Futures that are completed or running will not be
+                cancelled.
+        """
+        pass
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.shutdown(wait=True)
+        return False
+
+
+class BrokenExecutor(RuntimeError):
+    """
+    Raised when a executor has become non-functional after a severe failure.
+    """
diff --git a/contrib/tools/python3/src/Lib/concurrent/futures/process.py b/contrib/tools/python3/src/Lib/concurrent/futures/process.py
new file mode 100644
index 0000000000..321608ab17
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/concurrent/futures/process.py
@@ -0,0 +1,845 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Implements ProcessPoolExecutor.
+
+The following diagram and text describe the data-flow through the system:
+
+|======================= In-process =====================|== Out-of-process ==|
+
++----------+     +----------+       +--------+     +-----------+    +---------+
+|          |  => | Work Ids |       |        |     | Call Q    |    | Process |
+|          |     +----------+       |        |     +-----------+    |  Pool   |
+|          |     | ...      |       |        |     | ...       |    +---------+
+|          |     | 6        |    => |        |  => | 5, call() | => |         |
+|          |     | 7        |       |        |     | ...       |    |         |
+| Process  |     | ...      |       | Local  |     +-----------+    | Process |
+|  Pool    |     +----------+       | Worker |                      |  #1..n  |
+| Executor |                        | Thread |                      |         |
+|          |     +----------- +     |        |     +-----------+    |         |
+|          | <=> | Work Items | <=> |        | <=  | Result Q  | <= |         |
+|          |     +------------+     |        |     +-----------+    |         |
+|          |     | 6: call()  |     |        |     | ...       |    |         |
+|          |     |    future  |     |        |     | 4, result |    |         |
+|          |     | ...        |     |        |     | 3, except |    |         |
++----------+     +------------+     +--------+     +-----------+    +---------+
+
+Executor.submit() called:
+- creates a uniquely numbered _WorkItem and adds it to the "Work Items" dict
+- adds the id of the _WorkItem to the "Work Ids" queue
+
+Local worker thread:
+- reads work ids from the "Work Ids" queue and looks up the corresponding
+  WorkItem from the "Work Items" dict: if the work item has been cancelled then
+  it is simply removed from the dict, otherwise it is repackaged as a
+  _CallItem and put in the "Call Q". New _CallItems are put in the "Call Q"
+  until "Call Q" is full. NOTE: the size of the "Call Q" is kept small because
+  calls placed in the "Call Q" can no longer be cancelled with Future.cancel().
+- reads _ResultItems from "Result Q", updates the future stored in the
+  "Work Items" dict and deletes the dict entry
+
+Process #1..n:
+- reads _CallItems from "Call Q", executes the calls, and puts the resulting
+  _ResultItems in "Result Q"
+"""
+
+__author__ = 'Brian Quinlan (brian@sweetapp.com)'
+
+import os
+from concurrent.futures import _base
+import queue
+import multiprocessing as mp
+import multiprocessing.connection
+from multiprocessing.queues import Queue
+import threading
+import weakref
+from functools import partial
+import itertools
+import sys
+from traceback import format_exception
+
+
+_threads_wakeups = weakref.WeakKeyDictionary()
+_global_shutdown = False
+
+
+class _ThreadWakeup:
+    def __init__(self):
+        self._closed = False
+        self._reader, self._writer = mp.Pipe(duplex=False)
+
+    def close(self):
+        if not self._closed:
+            self._closed = True
+            self._writer.close()
+            self._reader.close()
+
+    def wakeup(self):
+        if not self._closed:
+            self._writer.send_bytes(b"")
+
+    def clear(self):
+        if not self._closed:
+            while self._reader.poll():
+                self._reader.recv_bytes()
+
+
+def _python_exit():
+    global _global_shutdown
+    _global_shutdown = True
+    items = list(_threads_wakeups.items())
+    for _, thread_wakeup in items:
+        # call not protected by ProcessPoolExecutor._shutdown_lock
+        thread_wakeup.wakeup()
+    for t, _ in items:
+        t.join()
+
+# Register for `_python_exit()` to be called just before joining all
+# non-daemon threads. This is used instead of `atexit.register()` for
+# compatibility with subinterpreters, which no longer support daemon threads.
+# See bpo-39812 for context.
+threading._register_atexit(_python_exit)
+
+# Controls how many more calls than processes will be queued in the call queue.
+# A smaller number will mean that processes spend more time idle waiting for
+# work while a larger number will make Future.cancel() succeed less frequently
+# (Futures in the call queue cannot be cancelled).
+EXTRA_QUEUED_CALLS = 1
+
+
+# On Windows, WaitForMultipleObjects is used to wait for processes to finish.
+# It can wait on, at most, 63 objects. There is an overhead of two objects:
+# - the result queue reader
+# - the thread wakeup reader
+_MAX_WINDOWS_WORKERS = 63 - 2
+
+# Hack to embed stringification of remote traceback in local traceback
+
+class _RemoteTraceback(Exception):
+    def __init__(self, tb):
+        self.tb = tb
+    def __str__(self):
+        return self.tb
+
+class _ExceptionWithTraceback:
+    def __init__(self, exc, tb):
+        tb = ''.join(format_exception(type(exc), exc, tb))
+        self.exc = exc
+        # Traceback object needs to be garbage-collected as its frames
+        # contain references to all the objects in the exception scope
+        self.exc.__traceback__ = None
+        self.tb = '\n"""\n%s"""' % tb
+    def __reduce__(self):
+        return _rebuild_exc, (self.exc, self.tb)
+
+def _rebuild_exc(exc, tb):
+    exc.__cause__ = _RemoteTraceback(tb)
+    return exc
+
+class _WorkItem(object):
+    def __init__(self, future, fn, args, kwargs):
+        self.future = future
+        self.fn = fn
+        self.args = args
+        self.kwargs = kwargs
+
+class _ResultItem(object):
+    def __init__(self, work_id, exception=None, result=None, exit_pid=None):
+        self.work_id = work_id
+        self.exception = exception
+        self.result = result
+        self.exit_pid = exit_pid
+
+class _CallItem(object):
+    def __init__(self, work_id, fn, args, kwargs):
+        self.work_id = work_id
+        self.fn = fn
+        self.args = args
+        self.kwargs = kwargs
+
+
+class _SafeQueue(Queue):
+    """Safe Queue set exception to the future object linked to a job"""
+    def __init__(self, max_size=0, *, ctx, pending_work_items, shutdown_lock,
+                 thread_wakeup):
+        self.pending_work_items = pending_work_items
+        self.shutdown_lock = shutdown_lock
+        self.thread_wakeup = thread_wakeup
+        super().__init__(max_size, ctx=ctx)
+
+    def _on_queue_feeder_error(self, e, obj):
+        if isinstance(obj, _CallItem):
+            tb = format_exception(type(e), e, e.__traceback__)
+            e.__cause__ = _RemoteTraceback('\n"""\n{}"""'.format(''.join(tb)))
+            work_item = self.pending_work_items.pop(obj.work_id, None)
+            with self.shutdown_lock:
+                self.thread_wakeup.wakeup()
+            # work_item can be None if another process terminated. In this
+            # case, the executor_manager_thread fails all work_items
+            # with BrokenProcessPool
+            if work_item is not None:
+                work_item.future.set_exception(e)
+        else:
+            super()._on_queue_feeder_error(e, obj)
+
+
+def _get_chunks(*iterables, chunksize):
+    """ Iterates over zip()ed iterables in chunks. """
+    it = zip(*iterables)
+    while True:
+        chunk = tuple(itertools.islice(it, chunksize))
+        if not chunk:
+            return
+        yield chunk
+
+
+def _process_chunk(fn, chunk):
+    """ Processes a chunk of an iterable passed to map.
+
+    Runs the function passed to map() on a chunk of the
+    iterable passed to map.
+
+    This function is run in a separate process.
+
+    """
+    return [fn(*args) for args in chunk]
+
+
+def _sendback_result(result_queue, work_id, result=None, exception=None,
+                     exit_pid=None):
+    """Safely send back the given result or exception"""
+    try:
+        result_queue.put(_ResultItem(work_id, result=result,
+                                     exception=exception, exit_pid=exit_pid))
+    except BaseException as e:
+        exc = _ExceptionWithTraceback(e, e.__traceback__)
+        result_queue.put(_ResultItem(work_id, exception=exc,
+                                     exit_pid=exit_pid))
+
+
+def _process_worker(call_queue, result_queue, initializer, initargs, max_tasks=None):
+    """Evaluates calls from call_queue and places the results in result_queue.
+
+    This worker is run in a separate process.
+
+    Args:
+        call_queue: A ctx.Queue of _CallItems that will be read and
+            evaluated by the worker.
+        result_queue: A ctx.Queue of _ResultItems that will written
+            to by the worker.
+        initializer: A callable initializer, or None
+        initargs: A tuple of args for the initializer
+    """
+    if initializer is not None:
+        try:
+            initializer(*initargs)
+        except BaseException:
+            _base.LOGGER.critical('Exception in initializer:', exc_info=True)
+            # The parent will notice that the process stopped and
+            # mark the pool broken
+            return
+    num_tasks = 0
+    exit_pid = None
+    while True:
+        call_item = call_queue.get(block=True)
+        if call_item is None:
+            # Wake up queue management thread
+            result_queue.put(os.getpid())
+            return
+
+        if max_tasks is not None:
+            num_tasks += 1
+            if num_tasks >= max_tasks:
+                exit_pid = os.getpid()
+
+        try:
+            r = call_item.fn(*call_item.args, **call_item.kwargs)
+        except BaseException as e:
+            exc = _ExceptionWithTraceback(e, e.__traceback__)
+            _sendback_result(result_queue, call_item.work_id, exception=exc,
+                             exit_pid=exit_pid)
+        else:
+            _sendback_result(result_queue, call_item.work_id, result=r,
+                             exit_pid=exit_pid)
+            del r
+
+        # Liberate the resource as soon as possible, to avoid holding onto
+        # open files or shared memory that is not needed anymore
+        del call_item
+
+        if exit_pid is not None:
+            return
+
+
+class _ExecutorManagerThread(threading.Thread):
+    """Manages the communication between this process and the worker processes.
+
+    The manager is run in a local thread.
+
+    Args:
+        executor: A reference to the ProcessPoolExecutor that owns
+            this thread. A weakref will be own by the manager as well as
+            references to internal objects used to introspect the state of
+            the executor.
+    """
+
+    def __init__(self, executor):
+        # Store references to necessary internals of the executor.
+
+        # A _ThreadWakeup to allow waking up the queue_manager_thread from the
+        # main Thread and avoid deadlocks caused by permanently locked queues.
+        self.thread_wakeup = executor._executor_manager_thread_wakeup
+        self.shutdown_lock = executor._shutdown_lock
+
+        # A weakref.ref to the ProcessPoolExecutor that owns this thread. Used
+        # to determine if the ProcessPoolExecutor has been garbage collected
+        # and that the manager can exit.
+        # When the executor gets garbage collected, the weakref callback
+        # will wake up the queue management thread so that it can terminate
+        # if there is no pending work item.
+        def weakref_cb(_,
+                       thread_wakeup=self.thread_wakeup,
+                       shutdown_lock=self.shutdown_lock):
+            mp.util.debug('Executor collected: triggering callback for'
+                          ' QueueManager wakeup')
+            with shutdown_lock:
+                thread_wakeup.wakeup()
+
+        self.executor_reference = weakref.ref(executor, weakref_cb)
+
+        # A list of the ctx.Process instances used as workers.
+        self.processes = executor._processes
+
+        # A ctx.Queue that will be filled with _CallItems derived from
+        # _WorkItems for processing by the process workers.
+        self.call_queue = executor._call_queue
+
+        # A ctx.SimpleQueue of _ResultItems generated by the process workers.
+        self.result_queue = executor._result_queue
+
+        # A queue.Queue of work ids e.g. Queue([5, 6, ...]).
+        self.work_ids_queue = executor._work_ids
+
+        # Maximum number of tasks a worker process can execute before
+        # exiting safely
+        self.max_tasks_per_child = executor._max_tasks_per_child
+
+        # A dict mapping work ids to _WorkItems e.g.
+        #     {5: <_WorkItem...>, 6: <_WorkItem...>, ...}
+        self.pending_work_items = executor._pending_work_items
+
+        super().__init__()
+
+    def run(self):
+        # Main loop for the executor manager thread.
+
+        while True:
+            self.add_call_item_to_queue()
+
+            result_item, is_broken, cause = self.wait_result_broken_or_wakeup()
+
+            if is_broken:
+                self.terminate_broken(cause)
+                return
+            if result_item is not None:
+                self.process_result_item(result_item)
+
+                process_exited = result_item.exit_pid is not None
+                if process_exited:
+                    p = self.processes.pop(result_item.exit_pid)
+                    p.join()
+
+                # Delete reference to result_item to avoid keeping references
+                # while waiting on new results.
+                del result_item
+
+                if executor := self.executor_reference():
+                    if process_exited:
+                        with self.shutdown_lock:
+                            executor._adjust_process_count()
+                    else:
+                        executor._idle_worker_semaphore.release()
+                    del executor
+
+            if self.is_shutting_down():
+                self.flag_executor_shutting_down()
+
+                # When only canceled futures remain in pending_work_items, our
+                # next call to wait_result_broken_or_wakeup would hang forever.
+                # This makes sure we have some running futures or none at all.
+                self.add_call_item_to_queue()
+
+                # Since no new work items can be added, it is safe to shutdown
+                # this thread if there are no pending work items.
+                if not self.pending_work_items:
+                    self.join_executor_internals()
+                    return
+
+    def add_call_item_to_queue(self):
+        # Fills call_queue with _WorkItems from pending_work_items.
+        # This function never blocks.
+        while True:
+            if self.call_queue.full():
+                return
+            try:
+                work_id = self.work_ids_queue.get(block=False)
+            except queue.Empty:
+                return
+            else:
+                work_item = self.pending_work_items[work_id]
+
+                if work_item.future.set_running_or_notify_cancel():
+                    self.call_queue.put(_CallItem(work_id,
+                                                  work_item.fn,
+                                                  work_item.args,
+                                                  work_item.kwargs),
+                                        block=True)
+                else:
+                    del self.pending_work_items[work_id]
+                    continue
+
+    def wait_result_broken_or_wakeup(self):
+        # Wait for a result to be ready in the result_queue while checking
+        # that all worker processes are still running, or for a wake up
+        # signal send. The wake up signals come either from new tasks being
+        # submitted, from the executor being shutdown/gc-ed, or from the
+        # shutdown of the python interpreter.
+        result_reader = self.result_queue._reader
+        assert not self.thread_wakeup._closed
+        wakeup_reader = self.thread_wakeup._reader
+        readers = [result_reader, wakeup_reader]
+        worker_sentinels = [p.sentinel for p in list(self.processes.values())]
+        ready = mp.connection.wait(readers + worker_sentinels)
+
+        cause = None
+        is_broken = True
+        result_item = None
+        if result_reader in ready:
+            try:
+                result_item = result_reader.recv()
+                is_broken = False
+            except BaseException as e:
+                cause = format_exception(type(e), e, e.__traceback__)
+
+        elif wakeup_reader in ready:
+            is_broken = False
+
+        with self.shutdown_lock:
+            self.thread_wakeup.clear()
+
+        return result_item, is_broken, cause
+
+    def process_result_item(self, result_item):
+        # Process the received a result_item. This can be either the PID of a
+        # worker that exited gracefully or a _ResultItem
+
+        if isinstance(result_item, int):
+            # Clean shutdown of a worker using its PID
+            # (avoids marking the executor broken)
+            assert self.is_shutting_down()
+            p = self.processes.pop(result_item)
+            p.join()
+            if not self.processes:
+                self.join_executor_internals()
+                return
+        else:
+            # Received a _ResultItem so mark the future as completed.
+            work_item = self.pending_work_items.pop(result_item.work_id, None)
+            # work_item can be None if another process terminated (see above)
+            if work_item is not None:
+                if result_item.exception:
+                    work_item.future.set_exception(result_item.exception)
+                else:
+                    work_item.future.set_result(result_item.result)
+
+    def is_shutting_down(self):
+        # Check whether we should start shutting down the executor.
+        executor = self.executor_reference()
+        # No more work items can be added if:
+        #   - The interpreter is shutting down OR
+        #   - The executor that owns this worker has been collected OR
+        #   - The executor that owns this worker has been shutdown.
+        return (_global_shutdown or executor is None
+                or executor._shutdown_thread)
+
+    def terminate_broken(self, cause):
+        # Terminate the executor because it is in a broken state. The cause
+        # argument can be used to display more information on the error that
+        # lead the executor into becoming broken.
+
+        # Mark the process pool broken so that submits fail right now.
+        executor = self.executor_reference()
+        if executor is not None:
+            executor._broken = ('A child process terminated '
+                                'abruptly, the process pool is not '
+                                'usable anymore')
+            executor._shutdown_thread = True
+            executor = None
+
+        # All pending tasks are to be marked failed with the following
+        # BrokenProcessPool error
+        bpe = BrokenProcessPool("A process in the process pool was "
+                                "terminated abruptly while the future was "
+                                "running or pending.")
+        if cause is not None:
+            bpe.__cause__ = _RemoteTraceback(
+                f"\n'''\n{''.join(cause)}'''")
+
+        # Mark pending tasks as failed.
+        for work_id, work_item in self.pending_work_items.items():
+            work_item.future.set_exception(bpe)
+            # Delete references to object. See issue16284
+            del work_item
+        self.pending_work_items.clear()
+
+        # Terminate remaining workers forcibly: the queues or their
+        # locks may be in a dirty state and block forever.
+        for p in self.processes.values():
+            p.terminate()
+
+        # Prevent queue writing to a pipe which is no longer read.
+        # https://github.com/python/cpython/issues/94777
+        self.call_queue._reader.close()
+
+        # clean up resources
+        self.join_executor_internals()
+
+    def flag_executor_shutting_down(self):
+        # Flag the executor as shutting down and cancel remaining tasks if
+        # requested as early as possible if it is not gc-ed yet.
+        executor = self.executor_reference()
+        if executor is not None:
+            executor._shutdown_thread = True
+            # Cancel pending work items if requested.
+            if executor._cancel_pending_futures:
+                # Cancel all pending futures and update pending_work_items
+                # to only have futures that are currently running.
+                new_pending_work_items = {}
+                for work_id, work_item in self.pending_work_items.items():
+                    if not work_item.future.cancel():
+                        new_pending_work_items[work_id] = work_item
+                self.pending_work_items = new_pending_work_items
+                # Drain work_ids_queue since we no longer need to
+                # add items to the call queue.
+                while True:
+                    try:
+                        self.work_ids_queue.get_nowait()
+                    except queue.Empty:
+                        break
+                # Make sure we do this only once to not waste time looping
+                # on running processes over and over.
+                executor._cancel_pending_futures = False
+
+    def shutdown_workers(self):
+        n_children_to_stop = self.get_n_children_alive()
+        n_sentinels_sent = 0
+        # Send the right number of sentinels, to make sure all children are
+        # properly terminated.
+        while (n_sentinels_sent < n_children_to_stop
+                and self.get_n_children_alive() > 0):
+            for i in range(n_children_to_stop - n_sentinels_sent):
+                try:
+                    self.call_queue.put_nowait(None)
+                    n_sentinels_sent += 1
+                except queue.Full:
+                    break
+
+    def join_executor_internals(self):
+        self.shutdown_workers()
+        # Release the queue's resources as soon as possible.
+        self.call_queue.close()
+        self.call_queue.join_thread()
+        with self.shutdown_lock:
+            self.thread_wakeup.close()
+        # If .join() is not called on the created processes then
+        # some ctx.Queue methods may deadlock on Mac OS X.
+        for p in self.processes.values():
+            p.join()
+
+    def get_n_children_alive(self):
+        # This is an upper bound on the number of children alive.
+        return sum(p.is_alive() for p in self.processes.values())
+
+
+_system_limits_checked = False
+_system_limited = None
+
+
+def _check_system_limits():
+    global _system_limits_checked, _system_limited
+    if _system_limits_checked:
+        if _system_limited:
+            raise NotImplementedError(_system_limited)
+    _system_limits_checked = True
+    try:
+        import multiprocessing.synchronize
+    except ImportError:
+        _system_limited = (
+            "This Python build lacks multiprocessing.synchronize, usually due "
+            "to named semaphores being unavailable on this platform."
+        )
+        raise NotImplementedError(_system_limited)
+    try:
+        nsems_max = os.sysconf("SC_SEM_NSEMS_MAX")
+    except (AttributeError, ValueError):
+        # sysconf not available or setting not available
+        return
+    if nsems_max == -1:
+        # indetermined limit, assume that limit is determined
+        # by available memory only
+        return
+    if nsems_max >= 256:
+        # minimum number of semaphores available
+        # according to POSIX
+        return
+    _system_limited = ("system provides too few semaphores (%d"
+                       " available, 256 necessary)" % nsems_max)
+    raise NotImplementedError(_system_limited)
+
+
+def _chain_from_iterable_of_lists(iterable):
+    """
+    Specialized implementation of itertools.chain.from_iterable.
+    Each item in *iterable* should be a list.  This function is
+    careful not to keep references to yielded objects.
+    """
+    for element in iterable:
+        element.reverse()
+        while element:
+            yield element.pop()
+
+
+class BrokenProcessPool(_base.BrokenExecutor):
+    """
+    Raised when a process in a ProcessPoolExecutor terminated abruptly
+    while a future was in the running state.
+    """
+
+
+class ProcessPoolExecutor(_base.Executor):
+    def __init__(self, max_workers=None, mp_context=None,
+                 initializer=None, initargs=(), *, max_tasks_per_child=None):
+        """Initializes a new ProcessPoolExecutor instance.
+
+        Args:
+            max_workers: The maximum number of processes that can be used to
+                execute the given calls. If None or not given then as many
+                worker processes will be created as the machine has processors.
+            mp_context: A multiprocessing context to launch the workers. This
+                object should provide SimpleQueue, Queue and Process. Useful
+                to allow specific multiprocessing start methods.
+            initializer: A callable used to initialize worker processes.
+            initargs: A tuple of arguments to pass to the initializer.
+            max_tasks_per_child: The maximum number of tasks a worker process
+                can complete before it will exit and be replaced with a fresh
+                worker process. The default of None means worker process will
+                live as long as the executor. Requires a non-'fork' mp_context
+                start method. When given, we default to using 'spawn' if no
+                mp_context is supplied.
+        """
+        _check_system_limits()
+
+        if max_workers is None:
+            self._max_workers = os.cpu_count() or 1
+            if sys.platform == 'win32':
+                self._max_workers = min(_MAX_WINDOWS_WORKERS,
+                                        self._max_workers)
+        else:
+            if max_workers <= 0:
+                raise ValueError("max_workers must be greater than 0")
+            elif (sys.platform == 'win32' and
+                max_workers > _MAX_WINDOWS_WORKERS):
+                raise ValueError(
+                    f"max_workers must be <= {_MAX_WINDOWS_WORKERS}")
+
+            self._max_workers = max_workers
+
+        if mp_context is None:
+            if max_tasks_per_child is not None:
+                mp_context = mp.get_context("spawn")
+            else:
+                mp_context = mp.get_context()
+        self._mp_context = mp_context
+
+        # https://github.com/python/cpython/issues/90622
+        self._safe_to_dynamically_spawn_children = (
+                self._mp_context.get_start_method(allow_none=False) != "fork")
+
+        if initializer is not None and not callable(initializer):
+            raise TypeError("initializer must be a callable")
+        self._initializer = initializer
+        self._initargs = initargs
+
+        if max_tasks_per_child is not None:
+            if not isinstance(max_tasks_per_child, int):
+                raise TypeError("max_tasks_per_child must be an integer")
+            elif max_tasks_per_child <= 0:
+                raise ValueError("max_tasks_per_child must be >= 1")
+            if self._mp_context.get_start_method(allow_none=False) == "fork":
+                # https://github.com/python/cpython/issues/90622
+                raise ValueError("max_tasks_per_child is incompatible with"
+                                 " the 'fork' multiprocessing start method;"
+                                 " supply a different mp_context.")
+        self._max_tasks_per_child = max_tasks_per_child
+
+        # Management thread
+        self._executor_manager_thread = None
+
+        # Map of pids to processes
+        self._processes = {}
+
+        # Shutdown is a two-step process.
+        self._shutdown_thread = False
+        self._shutdown_lock = threading.Lock()
+        self._idle_worker_semaphore = threading.Semaphore(0)
+        self._broken = False
+        self._queue_count = 0
+        self._pending_work_items = {}
+        self._cancel_pending_futures = False
+
+        # _ThreadWakeup is a communication channel used to interrupt the wait
+        # of the main loop of executor_manager_thread from another thread (e.g.
+        # when calling executor.submit or executor.shutdown). We do not use the
+        # _result_queue to send wakeup signals to the executor_manager_thread
+        # as it could result in a deadlock if a worker process dies with the
+        # _result_queue write lock still acquired.
+        #
+        # _shutdown_lock must be locked to access _ThreadWakeup.
+        self._executor_manager_thread_wakeup = _ThreadWakeup()
+
+        # Create communication channels for the executor
+        # Make the call queue slightly larger than the number of processes to
+        # prevent the worker processes from idling. But don't make it too big
+        # because futures in the call queue cannot be cancelled.
+        queue_size = self._max_workers + EXTRA_QUEUED_CALLS
+        self._call_queue = _SafeQueue(
+            max_size=queue_size, ctx=self._mp_context,
+            pending_work_items=self._pending_work_items,
+            shutdown_lock=self._shutdown_lock,
+            thread_wakeup=self._executor_manager_thread_wakeup)
+        # Killed worker processes can produce spurious "broken pipe"
+        # tracebacks in the queue's own worker thread. But we detect killed
+        # processes anyway, so silence the tracebacks.
+        self._call_queue._ignore_epipe = True
+        self._result_queue = mp_context.SimpleQueue()
+        self._work_ids = queue.Queue()
+
+    def _start_executor_manager_thread(self):
+        if self._executor_manager_thread is None:
+            # Start the processes so that their sentinels are known.
+            if not self._safe_to_dynamically_spawn_children:  # ie, using fork.
+                self._launch_processes()
+            self._executor_manager_thread = _ExecutorManagerThread(self)
+            self._executor_manager_thread.start()
+            _threads_wakeups[self._executor_manager_thread] = \
+                self._executor_manager_thread_wakeup
+
+    def _adjust_process_count(self):
+        # if there's an idle process, we don't need to spawn a new one.
+        if self._idle_worker_semaphore.acquire(blocking=False):
+            return
+
+        process_count = len(self._processes)
+        if process_count < self._max_workers:
+            # Assertion disabled as this codepath is also used to replace a
+            # worker that unexpectedly dies, even when using the 'fork' start
+            # method. That means there is still a potential deadlock bug. If a
+            # 'fork' mp_context worker dies, we'll be forking a new one when
+            # we know a thread is running (self._executor_manager_thread).
+            #assert self._safe_to_dynamically_spawn_children or not self._executor_manager_thread, 'https://github.com/python/cpython/issues/90622'
+            self._spawn_process()
+
+    def _launch_processes(self):
+        # https://github.com/python/cpython/issues/90622
+        assert not self._executor_manager_thread, (
+                'Processes cannot be fork()ed after the thread has started, '
+                'deadlock in the child processes could result.')
+        for _ in range(len(self._processes), self._max_workers):
+            self._spawn_process()
+
+    def _spawn_process(self):
+        p = self._mp_context.Process(
+            target=_process_worker,
+            args=(self._call_queue,
+                  self._result_queue,
+                  self._initializer,
+                  self._initargs,
+                  self._max_tasks_per_child))
+        p.start()
+        self._processes[p.pid] = p
+
+    def submit(self, fn, /, *args, **kwargs):
+        with self._shutdown_lock:
+            if self._broken:
+                raise BrokenProcessPool(self._broken)
+            if self._shutdown_thread:
+                raise RuntimeError('cannot schedule new futures after shutdown')
+            if _global_shutdown:
+                raise RuntimeError('cannot schedule new futures after '
+                                   'interpreter shutdown')
+
+            f = _base.Future()
+            w = _WorkItem(f, fn, args, kwargs)
+
+            self._pending_work_items[self._queue_count] = w
+            self._work_ids.put(self._queue_count)
+            self._queue_count += 1
+            # Wake up queue management thread
+            self._executor_manager_thread_wakeup.wakeup()
+
+            if self._safe_to_dynamically_spawn_children:
+                self._adjust_process_count()
+            self._start_executor_manager_thread()
+            return f
+    submit.__doc__ = _base.Executor.submit.__doc__
+
+    def map(self, fn, *iterables, timeout=None, chunksize=1):
+        """Returns an iterator equivalent to map(fn, iter).
+
+        Args:
+            fn: A callable that will take as many arguments as there are
+                passed iterables.
+            timeout: The maximum number of seconds to wait. If None, then there
+                is no limit on the wait time.
+            chunksize: If greater than one, the iterables will be chopped into
+                chunks of size chunksize and submitted to the process pool.
+                If set to one, the items in the list will be sent one at a time.
+
+        Returns:
+            An iterator equivalent to: map(func, *iterables) but the calls may
+            be evaluated out-of-order.
+
+        Raises:
+            TimeoutError: If the entire result iterator could not be generated
+                before the given timeout.
+            Exception: If fn(*args) raises for any values.
+        """
+        if chunksize < 1:
+            raise ValueError("chunksize must be >= 1.")
+
+        results = super().map(partial(_process_chunk, fn),
+                              _get_chunks(*iterables, chunksize=chunksize),
+                              timeout=timeout)
+        return _chain_from_iterable_of_lists(results)
+
+    def shutdown(self, wait=True, *, cancel_futures=False):
+        with self._shutdown_lock:
+            self._cancel_pending_futures = cancel_futures
+            self._shutdown_thread = True
+            if self._executor_manager_thread_wakeup is not None:
+                # Wake up queue management thread
+                self._executor_manager_thread_wakeup.wakeup()
+
+        if self._executor_manager_thread is not None and wait:
+            self._executor_manager_thread.join()
+        # To reduce the risk of opening too many files, remove references to
+        # objects that use file descriptors.
+        self._executor_manager_thread = None
+        self._call_queue = None
+        if self._result_queue is not None and wait:
+            self._result_queue.close()
+        self._result_queue = None
+        self._processes = None
+        self._executor_manager_thread_wakeup = None
+
+    shutdown.__doc__ = _base.Executor.shutdown.__doc__
diff --git a/contrib/tools/python3/src/Lib/concurrent/futures/thread.py b/contrib/tools/python3/src/Lib/concurrent/futures/thread.py
new file mode 100644
index 0000000000..51c942f51a
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/concurrent/futures/thread.py
@@ -0,0 +1,236 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Implements ThreadPoolExecutor."""
+
+__author__ = 'Brian Quinlan (brian@sweetapp.com)'
+
+from concurrent.futures import _base
+import itertools
+import queue
+import threading
+import types
+import weakref
+import os
+
+
+_threads_queues = weakref.WeakKeyDictionary()
+_shutdown = False
+# Lock that ensures that new workers are not created while the interpreter is
+# shutting down. Must be held while mutating _threads_queues and _shutdown.
+_global_shutdown_lock = threading.Lock()
+
+def _python_exit():
+    global _shutdown
+    with _global_shutdown_lock:
+        _shutdown = True
+    items = list(_threads_queues.items())
+    for t, q in items:
+        q.put(None)
+    for t, q in items:
+        t.join()
+
+# Register for `_python_exit()` to be called just before joining all
+# non-daemon threads. This is used instead of `atexit.register()` for
+# compatibility with subinterpreters, which no longer support daemon threads.
+# See bpo-39812 for context.
+threading._register_atexit(_python_exit)
+
+# At fork, reinitialize the `_global_shutdown_lock` lock in the child process
+if hasattr(os, 'register_at_fork'):
+    os.register_at_fork(before=_global_shutdown_lock.acquire,
+                        after_in_child=_global_shutdown_lock._at_fork_reinit,
+                        after_in_parent=_global_shutdown_lock.release)
+
+
+class _WorkItem(object):
+    def __init__(self, future, fn, args, kwargs):
+        self.future = future
+        self.fn = fn
+        self.args = args
+        self.kwargs = kwargs
+
+    def run(self):
+        if not self.future.set_running_or_notify_cancel():
+            return
+
+        try:
+            result = self.fn(*self.args, **self.kwargs)
+        except BaseException as exc:
+            self.future.set_exception(exc)
+            # Break a reference cycle with the exception 'exc'
+            self = None
+        else:
+            self.future.set_result(result)
+
+    __class_getitem__ = classmethod(types.GenericAlias)
+
+
+def _worker(executor_reference, work_queue, initializer, initargs):
+    if initializer is not None:
+        try:
+            initializer(*initargs)
+        except BaseException:
+            _base.LOGGER.critical('Exception in initializer:', exc_info=True)
+            executor = executor_reference()
+            if executor is not None:
+                executor._initializer_failed()
+            return
+    try:
+        while True:
+            work_item = work_queue.get(block=True)
+            if work_item is not None:
+                work_item.run()
+                # Delete references to object. See issue16284
+                del work_item
+
+                # attempt to increment idle count
+                executor = executor_reference()
+                if executor is not None:
+                    executor._idle_semaphore.release()
+                del executor
+                continue
+
+            executor = executor_reference()
+            # Exit if:
+            #   - The interpreter is shutting down OR
+            #   - The executor that owns the worker has been collected OR
+            #   - The executor that owns the worker has been shutdown.
+            if _shutdown or executor is None or executor._shutdown:
+                # Flag the executor as shutting down as early as possible if it
+                # is not gc-ed yet.
+                if executor is not None:
+                    executor._shutdown = True
+                # Notice other workers
+                work_queue.put(None)
+                return
+            del executor
+    except BaseException:
+        _base.LOGGER.critical('Exception in worker', exc_info=True)
+
+
+class BrokenThreadPool(_base.BrokenExecutor):
+    """
+    Raised when a worker thread in a ThreadPoolExecutor failed initializing.
+    """
+
+
+class ThreadPoolExecutor(_base.Executor):
+
+    # Used to assign unique thread names when thread_name_prefix is not supplied.
+    _counter = itertools.count().__next__
+
+    def __init__(self, max_workers=None, thread_name_prefix='',
+                 initializer=None, initargs=()):
+        """Initializes a new ThreadPoolExecutor instance.
+
+        Args:
+            max_workers: The maximum number of threads that can be used to
+                execute the given calls.
+            thread_name_prefix: An optional name prefix to give our threads.
+            initializer: A callable used to initialize worker threads.
+            initargs: A tuple of arguments to pass to the initializer.
+        """
+        if max_workers is None:
+            # ThreadPoolExecutor is often used to:
+            # * CPU bound task which releases GIL
+            # * I/O bound task (which releases GIL, of course)
+            #
+            # We use cpu_count + 4 for both types of tasks.
+            # But we limit it to 32 to avoid consuming surprisingly large resource
+            # on many core machine.
+            max_workers = min(32, (os.cpu_count() or 1) + 4)
+        if max_workers <= 0:
+            raise ValueError("max_workers must be greater than 0")
+
+        if initializer is not None and not callable(initializer):
+            raise TypeError("initializer must be a callable")
+
+        self._max_workers = max_workers
+        self._work_queue = queue.SimpleQueue()
+        self._idle_semaphore = threading.Semaphore(0)
+        self._threads = set()
+        self._broken = False
+        self._shutdown = False
+        self._shutdown_lock = threading.Lock()
+        self._thread_name_prefix = (thread_name_prefix or
+                                    ("ThreadPoolExecutor-%d" % self._counter()))
+        self._initializer = initializer
+        self._initargs = initargs
+
+    def submit(self, fn, /, *args, **kwargs):
+        with self._shutdown_lock, _global_shutdown_lock:
+            if self._broken:
+                raise BrokenThreadPool(self._broken)
+
+            if self._shutdown:
+                raise RuntimeError('cannot schedule new futures after shutdown')
+            if _shutdown:
+                raise RuntimeError('cannot schedule new futures after '
+                                   'interpreter shutdown')
+
+            f = _base.Future()
+            w = _WorkItem(f, fn, args, kwargs)
+
+            self._work_queue.put(w)
+            self._adjust_thread_count()
+            return f
+    submit.__doc__ = _base.Executor.submit.__doc__
+
+    def _adjust_thread_count(self):
+        # if idle threads are available, don't spin new threads
+        if self._idle_semaphore.acquire(timeout=0):
+            return
+
+        # When the executor gets lost, the weakref callback will wake up
+        # the worker threads.
+        def weakref_cb(_, q=self._work_queue):
+            q.put(None)
+
+        num_threads = len(self._threads)
+        if num_threads < self._max_workers:
+            thread_name = '%s_%d' % (self._thread_name_prefix or self,
+                                     num_threads)
+            t = threading.Thread(name=thread_name, target=_worker,
+                                 args=(weakref.ref(self, weakref_cb),
+                                       self._work_queue,
+                                       self._initializer,
+                                       self._initargs))
+            t.start()
+            self._threads.add(t)
+            _threads_queues[t] = self._work_queue
+
+    def _initializer_failed(self):
+        with self._shutdown_lock:
+            self._broken = ('A thread initializer failed, the thread pool '
+                            'is not usable anymore')
+            # Drain work queue and mark pending futures failed
+            while True:
+                try:
+                    work_item = self._work_queue.get_nowait()
+                except queue.Empty:
+                    break
+                if work_item is not None:
+                    work_item.future.set_exception(BrokenThreadPool(self._broken))
+
+    def shutdown(self, wait=True, *, cancel_futures=False):
+        with self._shutdown_lock:
+            self._shutdown = True
+            if cancel_futures:
+                # Drain all work items from the queue, and then cancel their
+                # associated futures.
+                while True:
+                    try:
+                        work_item = self._work_queue.get_nowait()
+                    except queue.Empty:
+                        break
+                    if work_item is not None:
+                        work_item.future.cancel()
+
+            # Send a wake-up to prevent threads calling
+            # _work_queue.get(block=True) from permanently blocking.
+            self._work_queue.put(None)
+        if wait:
+            for t in self._threads:
+                t.join()
+    shutdown.__doc__ = _base.Executor.shutdown.__doc__