Library import 16 (#2433)

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1 files changed, 1706 insertions, 0 deletions

diff --git a/contrib/tools/python3/Lib/threading.py b/contrib/tools/python3/Lib/threading.py
new file mode 100644
index 0000000000..98cb43c697
--- /dev/null
+++ b/contrib/tools/python3/Lib/threading.py
@@ -0,0 +1,1706 @@
+"""Thread module emulating a subset of Java's threading model."""
+
+import os as _os
+import sys as _sys
+import _thread
+import functools
+
+from time import monotonic as _time
+from _weakrefset import WeakSet
+from itertools import count as _count
+try:
+    from _collections import deque as _deque
+except ImportError:
+    from collections import deque as _deque
+
+# Note regarding PEP 8 compliant names
+#  This threading model was originally inspired by Java, and inherited
+# the convention of camelCase function and method names from that
+# language. Those original names are not in any imminent danger of
+# being deprecated (even for Py3k),so this module provides them as an
+# alias for the PEP 8 compliant names
+# Note that using the new PEP 8 compliant names facilitates substitution
+# with the multiprocessing module, which doesn't provide the old
+# Java inspired names.
+
+__all__ = ['get_ident', 'active_count', 'Condition', 'current_thread',
+           'enumerate', 'main_thread', 'TIMEOUT_MAX',
+           'Event', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Thread',
+           'Barrier', 'BrokenBarrierError', 'Timer', 'ThreadError',
+           'setprofile', 'settrace', 'local', 'stack_size',
+           'excepthook', 'ExceptHookArgs', 'gettrace', 'getprofile',
+           'setprofile_all_threads','settrace_all_threads']
+
+# Rename some stuff so "from threading import *" is safe
+_start_new_thread = _thread.start_new_thread
+_daemon_threads_allowed = _thread.daemon_threads_allowed
+_allocate_lock = _thread.allocate_lock
+_set_sentinel = _thread._set_sentinel
+get_ident = _thread.get_ident
+try:
+    _is_main_interpreter = _thread._is_main_interpreter
+except AttributeError:
+    # See https://github.com/python/cpython/issues/112826.
+    # We can pretend a subinterpreter is the main interpreter for the
+    # sake of _shutdown(), since that only means we do not wait for the
+    # subinterpreter's threads to finish.  Instead, they will be stopped
+    # later by the mechanism we use for daemon threads.  The likelihood
+    # of this case is small because rarely will the _thread module be
+    # replaced by a module without _is_main_interpreter().
+    # Furthermore, this is all irrelevant in applications
+    # that do not use subinterpreters.
+    def _is_main_interpreter():
+        return True
+try:
+    get_native_id = _thread.get_native_id
+    _HAVE_THREAD_NATIVE_ID = True
+    __all__.append('get_native_id')
+except AttributeError:
+    _HAVE_THREAD_NATIVE_ID = False
+ThreadError = _thread.error
+try:
+    _CRLock = _thread.RLock
+except AttributeError:
+    _CRLock = None
+TIMEOUT_MAX = _thread.TIMEOUT_MAX
+del _thread
+
+
+# Support for profile and trace hooks
+
+_profile_hook = None
+_trace_hook = None
+
+def setprofile(func):
+    """Set a profile function for all threads started from the threading module.
+
+    The func will be passed to sys.setprofile() for each thread, before its
+    run() method is called.
+    """
+    global _profile_hook
+    _profile_hook = func
+
+def setprofile_all_threads(func):
+    """Set a profile function for all threads started from the threading module
+    and all Python threads that are currently executing.
+
+    The func will be passed to sys.setprofile() for each thread, before its
+    run() method is called.
+    """
+    setprofile(func)
+    _sys._setprofileallthreads(func)
+
+def getprofile():
+    """Get the profiler function as set by threading.setprofile()."""
+    return _profile_hook
+
+def settrace(func):
+    """Set a trace function for all threads started from the threading module.
+
+    The func will be passed to sys.settrace() for each thread, before its run()
+    method is called.
+    """
+    global _trace_hook
+    _trace_hook = func
+
+def settrace_all_threads(func):
+    """Set a trace function for all threads started from the threading module
+    and all Python threads that are currently executing.
+
+    The func will be passed to sys.settrace() for each thread, before its run()
+    method is called.
+    """
+    settrace(func)
+    _sys._settraceallthreads(func)
+
+def gettrace():
+    """Get the trace function as set by threading.settrace()."""
+    return _trace_hook
+
+# Synchronization classes
+
+Lock = _allocate_lock
+
+def RLock(*args, **kwargs):
+    """Factory function that returns a new reentrant lock.
+
+    A reentrant lock must be released by the thread that acquired it. Once a
+    thread has acquired a reentrant lock, the same thread may acquire it again
+    without blocking; the thread must release it once for each time it has
+    acquired it.
+
+    """
+    if _CRLock is None:
+        return _PyRLock(*args, **kwargs)
+    return _CRLock(*args, **kwargs)
+
+class _RLock:
+    """This class implements reentrant lock objects.
+
+    A reentrant lock must be released by the thread that acquired it. Once a
+    thread has acquired a reentrant lock, the same thread may acquire it
+    again without blocking; the thread must release it once for each time it
+    has acquired it.
+
+    """
+
+    def __init__(self):
+        self._block = _allocate_lock()
+        self._owner = None
+        self._count = 0
+
+    def __repr__(self):
+        owner = self._owner
+        try:
+            owner = _active[owner].name
+        except KeyError:
+            pass
+        return "<%s %s.%s object owner=%r count=%d at %s>" % (
+            "locked" if self._block.locked() else "unlocked",
+            self.__class__.__module__,
+            self.__class__.__qualname__,
+            owner,
+            self._count,
+            hex(id(self))
+        )
+
+    def _at_fork_reinit(self):
+        self._block._at_fork_reinit()
+        self._owner = None
+        self._count = 0
+
+    def acquire(self, blocking=True, timeout=-1):
+        """Acquire a lock, blocking or non-blocking.
+
+        When invoked without arguments: if this thread already owns the lock,
+        increment the recursion level by one, and return immediately. Otherwise,
+        if another thread owns the lock, block until the lock is unlocked. Once
+        the lock is unlocked (not owned by any thread), then grab ownership, set
+        the recursion level to one, and return. If more than one thread is
+        blocked waiting until the lock is unlocked, only one at a time will be
+        able to grab ownership of the lock. There is no return value in this
+        case.
+
+        When invoked with the blocking argument set to true, do the same thing
+        as when called without arguments, and return true.
+
+        When invoked with the blocking argument set to false, do not block. If a
+        call without an argument would block, return false immediately;
+        otherwise, do the same thing as when called without arguments, and
+        return true.
+
+        When invoked with the floating-point timeout argument set to a positive
+        value, block for at most the number of seconds specified by timeout
+        and as long as the lock cannot be acquired.  Return true if the lock has
+        been acquired, false if the timeout has elapsed.
+
+        """
+        me = get_ident()
+        if self._owner == me:
+            self._count += 1
+            return 1
+        rc = self._block.acquire(blocking, timeout)
+        if rc:
+            self._owner = me
+            self._count = 1
+        return rc
+
+    __enter__ = acquire
+
+    def release(self):
+        """Release a lock, decrementing the recursion level.
+
+        If after the decrement it is zero, reset the lock to unlocked (not owned
+        by any thread), and if any other threads are blocked waiting for the
+        lock to become unlocked, allow exactly one of them to proceed. If after
+        the decrement the recursion level is still nonzero, the lock remains
+        locked and owned by the calling thread.
+
+        Only call this method when the calling thread owns the lock. A
+        RuntimeError is raised if this method is called when the lock is
+        unlocked.
+
+        There is no return value.
+
+        """
+        if self._owner != get_ident():
+            raise RuntimeError("cannot release un-acquired lock")
+        self._count = count = self._count - 1
+        if not count:
+            self._owner = None
+            self._block.release()
+
+    def __exit__(self, t, v, tb):
+        self.release()
+
+    # Internal methods used by condition variables
+
+    def _acquire_restore(self, state):
+        self._block.acquire()
+        self._count, self._owner = state
+
+    def _release_save(self):
+        if self._count == 0:
+            raise RuntimeError("cannot release un-acquired lock")
+        count = self._count
+        self._count = 0
+        owner = self._owner
+        self._owner = None
+        self._block.release()
+        return (count, owner)
+
+    def _is_owned(self):
+        return self._owner == get_ident()
+
+    # Internal method used for reentrancy checks
+
+    def _recursion_count(self):
+        if self._owner != get_ident():
+            return 0
+        return self._count
+
+_PyRLock = _RLock
+
+
+class Condition:
+    """Class that implements a condition variable.
+
+    A condition variable allows one or more threads to wait until they are
+    notified by another thread.
+
+    If the lock argument is given and not None, it must be a Lock or RLock
+    object, and it is used as the underlying lock. Otherwise, a new RLock object
+    is created and used as the underlying lock.
+
+    """
+
+    def __init__(self, lock=None):
+        if lock is None:
+            lock = RLock()
+        self._lock = lock
+        # Export the lock's acquire() and release() methods
+        self.acquire = lock.acquire
+        self.release = lock.release
+        # If the lock defines _release_save() and/or _acquire_restore(),
+        # these override the default implementations (which just call
+        # release() and acquire() on the lock).  Ditto for _is_owned().
+        if hasattr(lock, '_release_save'):
+            self._release_save = lock._release_save
+        if hasattr(lock, '_acquire_restore'):
+            self._acquire_restore = lock._acquire_restore
+        if hasattr(lock, '_is_owned'):
+            self._is_owned = lock._is_owned
+        self._waiters = _deque()
+
+    def _at_fork_reinit(self):
+        self._lock._at_fork_reinit()
+        self._waiters.clear()
+
+    def __enter__(self):
+        return self._lock.__enter__()
+
+    def __exit__(self, *args):
+        return self._lock.__exit__(*args)
+
+    def __repr__(self):
+        return "<Condition(%s, %d)>" % (self._lock, len(self._waiters))
+
+    def _release_save(self):
+        self._lock.release()           # No state to save
+
+    def _acquire_restore(self, x):
+        self._lock.acquire()           # Ignore saved state
+
+    def _is_owned(self):
+        # Return True if lock is owned by current_thread.
+        # This method is called only if _lock doesn't have _is_owned().
+        if self._lock.acquire(False):
+            self._lock.release()
+            return False
+        else:
+            return True
+
+    def wait(self, timeout=None):
+        """Wait until notified or until a timeout occurs.
+
+        If the calling thread has not acquired the lock when this method is
+        called, a RuntimeError is raised.
+
+        This method releases the underlying lock, and then blocks until it is
+        awakened by a notify() or notify_all() call for the same condition
+        variable in another thread, or until the optional timeout occurs. Once
+        awakened or timed out, it re-acquires the lock and returns.
+
+        When the timeout argument is present and not None, it should be a
+        floating point number specifying a timeout for the operation in seconds
+        (or fractions thereof).
+
+        When the underlying lock is an RLock, it is not released using its
+        release() method, since this may not actually unlock the lock when it
+        was acquired multiple times recursively. Instead, an internal interface
+        of the RLock class is used, which really unlocks it even when it has
+        been recursively acquired several times. Another internal interface is
+        then used to restore the recursion level when the lock is reacquired.
+
+        """
+        if not self._is_owned():
+            raise RuntimeError("cannot wait on un-acquired lock")
+        waiter = _allocate_lock()
+        waiter.acquire()
+        self._waiters.append(waiter)
+        saved_state = self._release_save()
+        gotit = False
+        try:    # restore state no matter what (e.g., KeyboardInterrupt)
+            if timeout is None:
+                waiter.acquire()
+                gotit = True
+            else:
+                if timeout > 0:
+                    gotit = waiter.acquire(True, timeout)
+                else:
+                    gotit = waiter.acquire(False)
+            return gotit
+        finally:
+            self._acquire_restore(saved_state)
+            if not gotit:
+                try:
+                    self._waiters.remove(waiter)
+                except ValueError:
+                    pass
+
+    def wait_for(self, predicate, timeout=None):
+        """Wait until a condition evaluates to True.
+
+        predicate should be a callable which result will be interpreted as a
+        boolean value.  A timeout may be provided giving the maximum time to
+        wait.
+
+        """
+        endtime = None
+        waittime = timeout
+        result = predicate()
+        while not result:
+            if waittime is not None:
+                if endtime is None:
+                    endtime = _time() + waittime
+                else:
+                    waittime = endtime - _time()
+                    if waittime <= 0:
+                        break
+            self.wait(waittime)
+            result = predicate()
+        return result
+
+    def notify(self, n=1):
+        """Wake up one or more threads waiting on this condition, if any.
+
+        If the calling thread has not acquired the lock when this method is
+        called, a RuntimeError is raised.
+
+        This method wakes up at most n of the threads waiting for the condition
+        variable; it is a no-op if no threads are waiting.
+
+        """
+        if not self._is_owned():
+            raise RuntimeError("cannot notify on un-acquired lock")
+        waiters = self._waiters
+        while waiters and n > 0:
+            waiter = waiters[0]
+            try:
+                waiter.release()
+            except RuntimeError:
+                # gh-92530: The previous call of notify() released the lock,
+                # but was interrupted before removing it from the queue.
+                # It can happen if a signal handler raises an exception,
+                # like CTRL+C which raises KeyboardInterrupt.
+                pass
+            else:
+                n -= 1
+            try:
+                waiters.remove(waiter)
+            except ValueError:
+                pass
+
+    def notify_all(self):
+        """Wake up all threads waiting on this condition.
+
+        If the calling thread has not acquired the lock when this method
+        is called, a RuntimeError is raised.
+
+        """
+        self.notify(len(self._waiters))
+
+    def notifyAll(self):
+        """Wake up all threads waiting on this condition.
+
+        This method is deprecated, use notify_all() instead.
+
+        """
+        import warnings
+        warnings.warn('notifyAll() is deprecated, use notify_all() instead',
+                      DeprecationWarning, stacklevel=2)
+        self.notify_all()
+
+
+class Semaphore:
+    """This class implements semaphore objects.
+
+    Semaphores manage a counter representing the number of release() calls minus
+    the number of acquire() calls, plus an initial value. The acquire() method
+    blocks if necessary until it can return without making the counter
+    negative. If not given, value defaults to 1.
+
+    """
+
+    # After Tim Peters' semaphore class, but not quite the same (no maximum)
+
+    def __init__(self, value=1):
+        if value < 0:
+            raise ValueError("semaphore initial value must be >= 0")
+        self._cond = Condition(Lock())
+        self._value = value
+
+    def __repr__(self):
+        cls = self.__class__
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" value={self._value}>")
+
+    def acquire(self, blocking=True, timeout=None):
+        """Acquire a semaphore, decrementing the internal counter by one.
+
+        When invoked without arguments: if the internal counter is larger than
+        zero on entry, decrement it by one and return immediately. If it is zero
+        on entry, block, waiting until some other thread has called release() to
+        make it larger than zero. This is done with proper interlocking so that
+        if multiple acquire() calls are blocked, release() will wake exactly one
+        of them up. The implementation may pick one at random, so the order in
+        which blocked threads are awakened should not be relied on. There is no
+        return value in this case.
+
+        When invoked with blocking set to true, do the same thing as when called
+        without arguments, and return true.
+
+        When invoked with blocking set to false, do not block. If a call without
+        an argument would block, return false immediately; otherwise, do the
+        same thing as when called without arguments, and return true.
+
+        When invoked with a timeout other than None, it will block for at
+        most timeout seconds.  If acquire does not complete successfully in
+        that interval, return false.  Return true otherwise.
+
+        """
+        if not blocking and timeout is not None:
+            raise ValueError("can't specify timeout for non-blocking acquire")
+        rc = False
+        endtime = None
+        with self._cond:
+            while self._value == 0:
+                if not blocking:
+                    break
+                if timeout is not None:
+                    if endtime is None:
+                        endtime = _time() + timeout
+                    else:
+                        timeout = endtime - _time()
+                        if timeout <= 0:
+                            break
+                self._cond.wait(timeout)
+            else:
+                self._value -= 1
+                rc = True
+        return rc
+
+    __enter__ = acquire
+
+    def release(self, n=1):
+        """Release a semaphore, incrementing the internal counter by one or more.
+
+        When the counter is zero on entry and another thread is waiting for it
+        to become larger than zero again, wake up that thread.
+
+        """
+        if n < 1:
+            raise ValueError('n must be one or more')
+        with self._cond:
+            self._value += n
+            self._cond.notify(n)
+
+    def __exit__(self, t, v, tb):
+        self.release()
+
+
+class BoundedSemaphore(Semaphore):
+    """Implements a bounded semaphore.
+
+    A bounded semaphore checks to make sure its current value doesn't exceed its
+    initial value. If it does, ValueError is raised. In most situations
+    semaphores are used to guard resources with limited capacity.
+
+    If the semaphore is released too many times it's a sign of a bug. If not
+    given, value defaults to 1.
+
+    Like regular semaphores, bounded semaphores manage a counter representing
+    the number of release() calls minus the number of acquire() calls, plus an
+    initial value. The acquire() method blocks if necessary until it can return
+    without making the counter negative. If not given, value defaults to 1.
+
+    """
+
+    def __init__(self, value=1):
+        super().__init__(value)
+        self._initial_value = value
+
+    def __repr__(self):
+        cls = self.__class__
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" value={self._value}/{self._initial_value}>")
+
+    def release(self, n=1):
+        """Release a semaphore, incrementing the internal counter by one or more.
+
+        When the counter is zero on entry and another thread is waiting for it
+        to become larger than zero again, wake up that thread.
+
+        If the number of releases exceeds the number of acquires,
+        raise a ValueError.
+
+        """
+        if n < 1:
+            raise ValueError('n must be one or more')
+        with self._cond:
+            if self._value + n > self._initial_value:
+                raise ValueError("Semaphore released too many times")
+            self._value += n
+            self._cond.notify(n)
+
+
+class Event:
+    """Class implementing event objects.
+
+    Events manage a flag that can be set to true with the set() method and reset
+    to false with the clear() method. The wait() method blocks until the flag is
+    true.  The flag is initially false.
+
+    """
+
+    # After Tim Peters' event class (without is_posted())
+
+    def __init__(self):
+        self._cond = Condition(Lock())
+        self._flag = False
+
+    def __repr__(self):
+        cls = self.__class__
+        status = 'set' if self._flag else 'unset'
+        return f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}: {status}>"
+
+    def _at_fork_reinit(self):
+        # Private method called by Thread._reset_internal_locks()
+        self._cond._at_fork_reinit()
+
+    def is_set(self):
+        """Return true if and only if the internal flag is true."""
+        return self._flag
+
+    def isSet(self):
+        """Return true if and only if the internal flag is true.
+
+        This method is deprecated, use is_set() instead.
+
+        """
+        import warnings
+        warnings.warn('isSet() is deprecated, use is_set() instead',
+                      DeprecationWarning, stacklevel=2)
+        return self.is_set()
+
+    def set(self):
+        """Set the internal flag to true.
+
+        All threads waiting for it to become true are awakened. Threads
+        that call wait() once the flag is true will not block at all.
+
+        """
+        with self._cond:
+            self._flag = True
+            self._cond.notify_all()
+
+    def clear(self):
+        """Reset the internal flag to false.
+
+        Subsequently, threads calling wait() will block until set() is called to
+        set the internal flag to true again.
+
+        """
+        with self._cond:
+            self._flag = False
+
+    def wait(self, timeout=None):
+        """Block until the internal flag is true.
+
+        If the internal flag is true on entry, return immediately. Otherwise,
+        block until another thread calls set() to set the flag to true, or until
+        the optional timeout occurs.
+
+        When the timeout argument is present and not None, it should be a
+        floating point number specifying a timeout for the operation in seconds
+        (or fractions thereof).
+
+        This method returns the internal flag on exit, so it will always return
+        True except if a timeout is given and the operation times out.
+
+        """
+        with self._cond:
+            signaled = self._flag
+            if not signaled:
+                signaled = self._cond.wait(timeout)
+            return signaled
+
+
+# A barrier class.  Inspired in part by the pthread_barrier_* api and
+# the CyclicBarrier class from Java.  See
+# http://sourceware.org/pthreads-win32/manual/pthread_barrier_init.html and
+# http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/
+#        CyclicBarrier.html
+# for information.
+# We maintain two main states, 'filling' and 'draining' enabling the barrier
+# to be cyclic.  Threads are not allowed into it until it has fully drained
+# since the previous cycle.  In addition, a 'resetting' state exists which is
+# similar to 'draining' except that threads leave with a BrokenBarrierError,
+# and a 'broken' state in which all threads get the exception.
+class Barrier:
+    """Implements a Barrier.
+
+    Useful for synchronizing a fixed number of threads at known synchronization
+    points.  Threads block on 'wait()' and are simultaneously awoken once they
+    have all made that call.
+
+    """
+
+    def __init__(self, parties, action=None, timeout=None):
+        """Create a barrier, initialised to 'parties' threads.
+
+        'action' is a callable which, when supplied, will be called by one of
+        the threads after they have all entered the barrier and just prior to
+        releasing them all. If a 'timeout' is provided, it is used as the
+        default for all subsequent 'wait()' calls.
+
+        """
+        self._cond = Condition(Lock())
+        self._action = action
+        self._timeout = timeout
+        self._parties = parties
+        self._state = 0  # 0 filling, 1 draining, -1 resetting, -2 broken
+        self._count = 0
+
+    def __repr__(self):
+        cls = self.__class__
+        if self.broken:
+            return f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}: broken>"
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" waiters={self.n_waiting}/{self.parties}>")
+
+    def wait(self, timeout=None):
+        """Wait for the barrier.
+
+        When the specified number of threads have started waiting, they are all
+        simultaneously awoken. If an 'action' was provided for the barrier, one
+        of the threads will have executed that callback prior to returning.
+        Returns an individual index number from 0 to 'parties-1'.
+
+        """
+        if timeout is None:
+            timeout = self._timeout
+        with self._cond:
+            self._enter() # Block while the barrier drains.
+            index = self._count
+            self._count += 1
+            try:
+                if index + 1 == self._parties:
+                    # We release the barrier
+                    self._release()
+                else:
+                    # We wait until someone releases us
+                    self._wait(timeout)
+                return index
+            finally:
+                self._count -= 1
+                # Wake up any threads waiting for barrier to drain.
+                self._exit()
+
+    # Block until the barrier is ready for us, or raise an exception
+    # if it is broken.
+    def _enter(self):
+        while self._state in (-1, 1):
+            # It is draining or resetting, wait until done
+            self._cond.wait()
+        #see if the barrier is in a broken state
+        if self._state < 0:
+            raise BrokenBarrierError
+        assert self._state == 0
+
+    # Optionally run the 'action' and release the threads waiting
+    # in the barrier.
+    def _release(self):
+        try:
+            if self._action:
+                self._action()
+            # enter draining state
+            self._state = 1
+            self._cond.notify_all()
+        except:
+            #an exception during the _action handler.  Break and reraise
+            self._break()
+            raise
+
+    # Wait in the barrier until we are released.  Raise an exception
+    # if the barrier is reset or broken.
+    def _wait(self, timeout):
+        if not self._cond.wait_for(lambda : self._state != 0, timeout):
+            #timed out.  Break the barrier
+            self._break()
+            raise BrokenBarrierError
+        if self._state < 0:
+            raise BrokenBarrierError
+        assert self._state == 1
+
+    # If we are the last thread to exit the barrier, signal any threads
+    # waiting for the barrier to drain.
+    def _exit(self):
+        if self._count == 0:
+            if self._state in (-1, 1):
+                #resetting or draining
+                self._state = 0
+                self._cond.notify_all()
+
+    def reset(self):
+        """Reset the barrier to the initial state.
+
+        Any threads currently waiting will get the BrokenBarrier exception
+        raised.
+
+        """
+        with self._cond:
+            if self._count > 0:
+                if self._state == 0:
+                    #reset the barrier, waking up threads
+                    self._state = -1
+                elif self._state == -2:
+                    #was broken, set it to reset state
+                    #which clears when the last thread exits
+                    self._state = -1
+            else:
+                self._state = 0
+            self._cond.notify_all()
+
+    def abort(self):
+        """Place the barrier into a 'broken' state.
+
+        Useful in case of error.  Any currently waiting threads and threads
+        attempting to 'wait()' will have BrokenBarrierError raised.
+
+        """
+        with self._cond:
+            self._break()
+
+    def _break(self):
+        # An internal error was detected.  The barrier is set to
+        # a broken state all parties awakened.
+        self._state = -2
+        self._cond.notify_all()
+
+    @property
+    def parties(self):
+        """Return the number of threads required to trip the barrier."""
+        return self._parties
+
+    @property
+    def n_waiting(self):
+        """Return the number of threads currently waiting at the barrier."""
+        # We don't need synchronization here since this is an ephemeral result
+        # anyway.  It returns the correct value in the steady state.
+        if self._state == 0:
+            return self._count
+        return 0
+
+    @property
+    def broken(self):
+        """Return True if the barrier is in a broken state."""
+        return self._state == -2
+
+# exception raised by the Barrier class
+class BrokenBarrierError(RuntimeError):
+    pass
+
+
+# Helper to generate new thread names
+_counter = _count(1).__next__
+def _newname(name_template):
+    return name_template % _counter()
+
+# Active thread administration.
+#
+# bpo-44422: Use a reentrant lock to allow reentrant calls to functions like
+# threading.enumerate().
+_active_limbo_lock = RLock()
+_active = {}    # maps thread id to Thread object
+_limbo = {}
+_dangling = WeakSet()
+
+# Set of Thread._tstate_lock locks of non-daemon threads used by _shutdown()
+# to wait until all Python thread states get deleted:
+# see Thread._set_tstate_lock().
+_shutdown_locks_lock = _allocate_lock()
+_shutdown_locks = set()
+
+def _maintain_shutdown_locks():
+    """
+    Drop any shutdown locks that don't correspond to running threads anymore.
+
+    Calling this from time to time avoids an ever-growing _shutdown_locks
+    set when Thread objects are not joined explicitly. See bpo-37788.
+
+    This must be called with _shutdown_locks_lock acquired.
+    """
+    # If a lock was released, the corresponding thread has exited
+    to_remove = [lock for lock in _shutdown_locks if not lock.locked()]
+    _shutdown_locks.difference_update(to_remove)
+
+
+# Main class for threads
+
+class Thread:
+    """A class that represents a thread of control.
+
+    This class can be safely subclassed in a limited fashion. There are two ways
+    to specify the activity: by passing a callable object to the constructor, or
+    by overriding the run() method in a subclass.
+
+    """
+
+    _initialized = False
+
+    def __init__(self, group=None, target=None, name=None,
+                 args=(), kwargs=None, *, daemon=None):
+        """This constructor should always be called with keyword arguments. Arguments are:
+
+        *group* should be None; reserved for future extension when a ThreadGroup
+        class is implemented.
+
+        *target* is the callable object to be invoked by the run()
+        method. Defaults to None, meaning nothing is called.
+
+        *name* is the thread name. By default, a unique name is constructed of
+        the form "Thread-N" where N is a small decimal number.
+
+        *args* is a list or tuple of arguments for the target invocation. Defaults to ().
+
+        *kwargs* is a dictionary of keyword arguments for the target
+        invocation. Defaults to {}.
+
+        If a subclass overrides the constructor, it must make sure to invoke
+        the base class constructor (Thread.__init__()) before doing anything
+        else to the thread.
+
+        """
+        assert group is None, "group argument must be None for now"
+        if kwargs is None:
+            kwargs = {}
+        if name:
+            name = str(name)
+        else:
+            name = _newname("Thread-%d")
+            if target is not None:
+                try:
+                    target_name = target.__name__
+                    name += f" ({target_name})"
+                except AttributeError:
+                    pass
+
+        self._target = target
+        self._name = name
+        self._args = args
+        self._kwargs = kwargs
+        if daemon is not None:
+            if daemon and not _daemon_threads_allowed():
+                raise RuntimeError('daemon threads are disabled in this (sub)interpreter')
+            self._daemonic = daemon
+        else:
+            self._daemonic = current_thread().daemon
+        self._ident = None
+        if _HAVE_THREAD_NATIVE_ID:
+            self._native_id = None
+        self._tstate_lock = None
+        self._started = Event()
+        self._is_stopped = False
+        self._initialized = True
+        # Copy of sys.stderr used by self._invoke_excepthook()
+        self._stderr = _sys.stderr
+        self._invoke_excepthook = _make_invoke_excepthook()
+        # For debugging and _after_fork()
+        _dangling.add(self)
+
+    def _reset_internal_locks(self, is_alive):
+        # private!  Called by _after_fork() to reset our internal locks as
+        # they may be in an invalid state leading to a deadlock or crash.
+        self._started._at_fork_reinit()
+        if is_alive:
+            # bpo-42350: If the fork happens when the thread is already stopped
+            # (ex: after threading._shutdown() has been called), _tstate_lock
+            # is None. Do nothing in this case.
+            if self._tstate_lock is not None:
+                self._tstate_lock._at_fork_reinit()
+                self._tstate_lock.acquire()
+        else:
+            # The thread isn't alive after fork: it doesn't have a tstate
+            # anymore.
+            self._is_stopped = True
+            self._tstate_lock = None
+
+    def __repr__(self):
+        assert self._initialized, "Thread.__init__() was not called"
+        status = "initial"
+        if self._started.is_set():
+            status = "started"
+        self.is_alive() # easy way to get ._is_stopped set when appropriate
+        if self._is_stopped:
+            status = "stopped"
+        if self._daemonic:
+            status += " daemon"
+        if self._ident is not None:
+            status += " %s" % self._ident
+        return "<%s(%s, %s)>" % (self.__class__.__name__, self._name, status)
+
+    def start(self):
+        """Start the thread's activity.
+
+        It must be called at most once per thread object. It arranges for the
+        object's run() method to be invoked in a separate thread of control.
+
+        This method will raise a RuntimeError if called more than once on the
+        same thread object.
+
+        """
+        if not self._initialized:
+            raise RuntimeError("thread.__init__() not called")
+
+        if self._started.is_set():
+            raise RuntimeError("threads can only be started once")
+
+        with _active_limbo_lock:
+            _limbo[self] = self
+        try:
+            _start_new_thread(self._bootstrap, ())
+        except Exception:
+            with _active_limbo_lock:
+                del _limbo[self]
+            raise
+        self._started.wait()
+
+    def run(self):
+        """Method representing the thread's activity.
+
+        You may override this method in a subclass. The standard run() method
+        invokes the callable object passed to the object's constructor as the
+        target argument, if any, with sequential and keyword arguments taken
+        from the args and kwargs arguments, respectively.
+
+        """
+        try:
+            if self._target is not None:
+                self._target(*self._args, **self._kwargs)
+        finally:
+            # Avoid a refcycle if the thread is running a function with
+            # an argument that has a member that points to the thread.
+            del self._target, self._args, self._kwargs
+
+    def _bootstrap(self):
+        # Wrapper around the real bootstrap code that ignores
+        # exceptions during interpreter cleanup.  Those typically
+        # happen when a daemon thread wakes up at an unfortunate
+        # moment, finds the world around it destroyed, and raises some
+        # random exception *** while trying to report the exception in
+        # _bootstrap_inner() below ***.  Those random exceptions
+        # don't help anybody, and they confuse users, so we suppress
+        # them.  We suppress them only when it appears that the world
+        # indeed has already been destroyed, so that exceptions in
+        # _bootstrap_inner() during normal business hours are properly
+        # reported.  Also, we only suppress them for daemonic threads;
+        # if a non-daemonic encounters this, something else is wrong.
+        try:
+            self._bootstrap_inner()
+        except:
+            if self._daemonic and _sys is None:
+                return
+            raise
+
+    def _set_ident(self):
+        self._ident = get_ident()
+
+    if _HAVE_THREAD_NATIVE_ID:
+        def _set_native_id(self):
+            self._native_id = get_native_id()
+
+    def _set_tstate_lock(self):
+        """
+        Set a lock object which will be released by the interpreter when
+        the underlying thread state (see pystate.h) gets deleted.
+        """
+        self._tstate_lock = _set_sentinel()
+        self._tstate_lock.acquire()
+
+        if not self.daemon:
+            with _shutdown_locks_lock:
+                _maintain_shutdown_locks()
+                _shutdown_locks.add(self._tstate_lock)
+
+    def _bootstrap_inner(self):
+        try:
+            self._set_ident()
+            self._set_tstate_lock()
+            if _HAVE_THREAD_NATIVE_ID:
+                self._set_native_id()
+            self._started.set()
+            with _active_limbo_lock:
+                _active[self._ident] = self
+                del _limbo[self]
+
+            if _trace_hook:
+                _sys.settrace(_trace_hook)
+            if _profile_hook:
+                _sys.setprofile(_profile_hook)
+
+            try:
+                self.run()
+            except:
+                self._invoke_excepthook(self)
+        finally:
+            self._delete()
+
+    def _stop(self):
+        # After calling ._stop(), .is_alive() returns False and .join() returns
+        # immediately.  ._tstate_lock must be released before calling ._stop().
+        #
+        # Normal case:  C code at the end of the thread's life
+        # (release_sentinel in _threadmodule.c) releases ._tstate_lock, and
+        # that's detected by our ._wait_for_tstate_lock(), called by .join()
+        # and .is_alive().  Any number of threads _may_ call ._stop()
+        # simultaneously (for example, if multiple threads are blocked in
+        # .join() calls), and they're not serialized.  That's harmless -
+        # they'll just make redundant rebindings of ._is_stopped and
+        # ._tstate_lock.  Obscure:  we rebind ._tstate_lock last so that the
+        # "assert self._is_stopped" in ._wait_for_tstate_lock() always works
+        # (the assert is executed only if ._tstate_lock is None).
+        #
+        # Special case:  _main_thread releases ._tstate_lock via this
+        # module's _shutdown() function.
+        lock = self._tstate_lock
+        if lock is not None:
+            assert not lock.locked()
+        self._is_stopped = True
+        self._tstate_lock = None
+        if not self.daemon:
+            with _shutdown_locks_lock:
+                # Remove our lock and other released locks from _shutdown_locks
+                _maintain_shutdown_locks()
+
+    def _delete(self):
+        "Remove current thread from the dict of currently running threads."
+        with _active_limbo_lock:
+            del _active[get_ident()]
+            # There must not be any python code between the previous line
+            # and after the lock is released.  Otherwise a tracing function
+            # could try to acquire the lock again in the same thread, (in
+            # current_thread()), and would block.
+
+    def join(self, timeout=None):
+        """Wait until the thread terminates.
+
+        This blocks the calling thread until the thread whose join() method is
+        called terminates -- either normally or through an unhandled exception
+        or until the optional timeout occurs.
+
+        When the timeout argument is present and not None, it should be a
+        floating point number specifying a timeout for the operation in seconds
+        (or fractions thereof). As join() always returns None, you must call
+        is_alive() after join() to decide whether a timeout happened -- if the
+        thread is still alive, the join() call timed out.
+
+        When the timeout argument is not present or None, the operation will
+        block until the thread terminates.
+
+        A thread can be join()ed many times.
+
+        join() raises a RuntimeError if an attempt is made to join the current
+        thread as that would cause a deadlock. It is also an error to join() a
+        thread before it has been started and attempts to do so raises the same
+        exception.
+
+        """
+        if not self._initialized:
+            raise RuntimeError("Thread.__init__() not called")
+        if not self._started.is_set():
+            raise RuntimeError("cannot join thread before it is started")
+        if self is current_thread():
+            raise RuntimeError("cannot join current thread")
+
+        if timeout is None:
+            self._wait_for_tstate_lock()
+        else:
+            # the behavior of a negative timeout isn't documented, but
+            # historically .join(timeout=x) for x<0 has acted as if timeout=0
+            self._wait_for_tstate_lock(timeout=max(timeout, 0))
+
+    def _wait_for_tstate_lock(self, block=True, timeout=-1):
+        # Issue #18808: wait for the thread state to be gone.
+        # At the end of the thread's life, after all knowledge of the thread
+        # is removed from C data structures, C code releases our _tstate_lock.
+        # This method passes its arguments to _tstate_lock.acquire().
+        # If the lock is acquired, the C code is done, and self._stop() is
+        # called.  That sets ._is_stopped to True, and ._tstate_lock to None.
+        lock = self._tstate_lock
+        if lock is None:
+            # already determined that the C code is done
+            assert self._is_stopped
+            return
+
+        try:
+            if lock.acquire(block, timeout):
+                lock.release()
+                self._stop()
+        except:
+            if lock.locked():
+                # bpo-45274: lock.acquire() acquired the lock, but the function
+                # was interrupted with an exception before reaching the
+                # lock.release(). It can happen if a signal handler raises an
+                # exception, like CTRL+C which raises KeyboardInterrupt.
+                lock.release()
+                self._stop()
+            raise
+
+    @property
+    def name(self):
+        """A string used for identification purposes only.
+
+        It has no semantics. Multiple threads may be given the same name. The
+        initial name is set by the constructor.
+
+        """
+        assert self._initialized, "Thread.__init__() not called"
+        return self._name
+
+    @name.setter
+    def name(self, name):
+        assert self._initialized, "Thread.__init__() not called"
+        self._name = str(name)
+
+    @property
+    def ident(self):
+        """Thread identifier of this thread or None if it has not been started.
+
+        This is a nonzero integer. See the get_ident() function. Thread
+        identifiers may be recycled when a thread exits and another thread is
+        created. The identifier is available even after the thread has exited.
+
+        """
+        assert self._initialized, "Thread.__init__() not called"
+        return self._ident
+
+    if _HAVE_THREAD_NATIVE_ID:
+        @property
+        def native_id(self):
+            """Native integral thread ID of this thread, or None if it has not been started.
+
+            This is a non-negative integer. See the get_native_id() function.
+            This represents the Thread ID as reported by the kernel.
+
+            """
+            assert self._initialized, "Thread.__init__() not called"
+            return self._native_id
+
+    def is_alive(self):
+        """Return whether the thread is alive.
+
+        This method returns True just before the run() method starts until just
+        after the run() method terminates. See also the module function
+        enumerate().
+
+        """
+        assert self._initialized, "Thread.__init__() not called"
+        if self._is_stopped or not self._started.is_set():
+            return False
+        self._wait_for_tstate_lock(False)
+        return not self._is_stopped
+
+    @property
+    def daemon(self):
+        """A boolean value indicating whether this thread is a daemon thread.
+
+        This must be set before start() is called, otherwise RuntimeError is
+        raised. Its initial value is inherited from the creating thread; the
+        main thread is not a daemon thread and therefore all threads created in
+        the main thread default to daemon = False.
+
+        The entire Python program exits when only daemon threads are left.
+
+        """
+        assert self._initialized, "Thread.__init__() not called"
+        return self._daemonic
+
+    @daemon.setter
+    def daemon(self, daemonic):
+        if not self._initialized:
+            raise RuntimeError("Thread.__init__() not called")
+        if daemonic and not _daemon_threads_allowed():
+            raise RuntimeError('daemon threads are disabled in this interpreter')
+        if self._started.is_set():
+            raise RuntimeError("cannot set daemon status of active thread")
+        self._daemonic = daemonic
+
+    def isDaemon(self):
+        """Return whether this thread is a daemon.
+
+        This method is deprecated, use the daemon attribute instead.
+
+        """
+        import warnings
+        warnings.warn('isDaemon() is deprecated, get the daemon attribute instead',
+                      DeprecationWarning, stacklevel=2)
+        return self.daemon
+
+    def setDaemon(self, daemonic):
+        """Set whether this thread is a daemon.
+
+        This method is deprecated, use the .daemon property instead.
+
+        """
+        import warnings
+        warnings.warn('setDaemon() is deprecated, set the daemon attribute instead',
+                      DeprecationWarning, stacklevel=2)
+        self.daemon = daemonic
+
+    def getName(self):
+        """Return a string used for identification purposes only.
+
+        This method is deprecated, use the name attribute instead.
+
+        """
+        import warnings
+        warnings.warn('getName() is deprecated, get the name attribute instead',
+                      DeprecationWarning, stacklevel=2)
+        return self.name
+
+    def setName(self, name):
+        """Set the name string for this thread.
+
+        This method is deprecated, use the name attribute instead.
+
+        """
+        import warnings
+        warnings.warn('setName() is deprecated, set the name attribute instead',
+                      DeprecationWarning, stacklevel=2)
+        self.name = name
+
+
+try:
+    from _thread import (_excepthook as excepthook,
+                         _ExceptHookArgs as ExceptHookArgs)
+except ImportError:
+    # Simple Python implementation if _thread._excepthook() is not available
+    from traceback import print_exception as _print_exception
+    from collections import namedtuple
+
+    _ExceptHookArgs = namedtuple(
+        'ExceptHookArgs',
+        'exc_type exc_value exc_traceback thread')
+
+    def ExceptHookArgs(args):
+        return _ExceptHookArgs(*args)
+
+    def excepthook(args, /):
+        """
+        Handle uncaught Thread.run() exception.
+        """
+        if args.exc_type == SystemExit:
+            # silently ignore SystemExit
+            return
+
+        if _sys is not None and _sys.stderr is not None:
+            stderr = _sys.stderr
+        elif args.thread is not None:
+            stderr = args.thread._stderr
+            if stderr is None:
+                # do nothing if sys.stderr is None and sys.stderr was None
+                # when the thread was created
+                return
+        else:
+            # do nothing if sys.stderr is None and args.thread is None
+            return
+
+        if args.thread is not None:
+            name = args.thread.name
+        else:
+            name = get_ident()
+        print(f"Exception in thread {name}:",
+              file=stderr, flush=True)
+        _print_exception(args.exc_type, args.exc_value, args.exc_traceback,
+                         file=stderr)
+        stderr.flush()
+
+
+# Original value of threading.excepthook
+__excepthook__ = excepthook
+
+
+def _make_invoke_excepthook():
+    # Create a local namespace to ensure that variables remain alive
+    # when _invoke_excepthook() is called, even if it is called late during
+    # Python shutdown. It is mostly needed for daemon threads.
+
+    old_excepthook = excepthook
+    old_sys_excepthook = _sys.excepthook
+    if old_excepthook is None:
+        raise RuntimeError("threading.excepthook is None")
+    if old_sys_excepthook is None:
+        raise RuntimeError("sys.excepthook is None")
+
+    sys_exc_info = _sys.exc_info
+    local_print = print
+    local_sys = _sys
+
+    def invoke_excepthook(thread):
+        global excepthook
+        try:
+            hook = excepthook
+            if hook is None:
+                hook = old_excepthook
+
+            args = ExceptHookArgs([*sys_exc_info(), thread])
+
+            hook(args)
+        except Exception as exc:
+            exc.__suppress_context__ = True
+            del exc
+
+            if local_sys is not None and local_sys.stderr is not None:
+                stderr = local_sys.stderr
+            else:
+                stderr = thread._stderr
+
+            local_print("Exception in threading.excepthook:",
+                        file=stderr, flush=True)
+
+            if local_sys is not None and local_sys.excepthook is not None:
+                sys_excepthook = local_sys.excepthook
+            else:
+                sys_excepthook = old_sys_excepthook
+
+            sys_excepthook(*sys_exc_info())
+        finally:
+            # Break reference cycle (exception stored in a variable)
+            args = None
+
+    return invoke_excepthook
+
+
+# The timer class was contributed by Itamar Shtull-Trauring
+
+class Timer(Thread):
+    """Call a function after a specified number of seconds:
+
+            t = Timer(30.0, f, args=None, kwargs=None)
+            t.start()
+            t.cancel()     # stop the timer's action if it's still waiting
+
+    """
+
+    def __init__(self, interval, function, args=None, kwargs=None):
+        Thread.__init__(self)
+        self.interval = interval
+        self.function = function
+        self.args = args if args is not None else []
+        self.kwargs = kwargs if kwargs is not None else {}
+        self.finished = Event()
+
+    def cancel(self):
+        """Stop the timer if it hasn't finished yet."""
+        self.finished.set()
+
+    def run(self):
+        self.finished.wait(self.interval)
+        if not self.finished.is_set():
+            self.function(*self.args, **self.kwargs)
+        self.finished.set()
+
+
+# Special thread class to represent the main thread
+
+class _MainThread(Thread):
+
+    def __init__(self):
+        Thread.__init__(self, name="MainThread", daemon=False)
+        self._set_tstate_lock()
+        self._started.set()
+        self._set_ident()
+        if _HAVE_THREAD_NATIVE_ID:
+            self._set_native_id()
+        with _active_limbo_lock:
+            _active[self._ident] = self
+
+
+# Dummy thread class to represent threads not started here.
+# These aren't garbage collected when they die, nor can they be waited for.
+# If they invoke anything in threading.py that calls current_thread(), they
+# leave an entry in the _active dict forever after.
+# Their purpose is to return *something* from current_thread().
+# They are marked as daemon threads so we won't wait for them
+# when we exit (conform previous semantics).
+
+class _DummyThread(Thread):
+
+    def __init__(self):
+        Thread.__init__(self, name=_newname("Dummy-%d"),
+                        daemon=_daemon_threads_allowed())
+        self._started.set()
+        self._set_ident()
+        if _HAVE_THREAD_NATIVE_ID:
+            self._set_native_id()
+        with _active_limbo_lock:
+            _active[self._ident] = self
+
+    def _stop(self):
+        pass
+
+    def is_alive(self):
+        assert not self._is_stopped and self._started.is_set()
+        return True
+
+    def join(self, timeout=None):
+        assert False, "cannot join a dummy thread"
+
+
+# Global API functions
+
+def current_thread():
+    """Return the current Thread object, corresponding to the caller's thread of control.
+
+    If the caller's thread of control was not created through the threading
+    module, a dummy thread object with limited functionality is returned.
+
+    """
+    try:
+        return _active[get_ident()]
+    except KeyError:
+        return _DummyThread()
+
+def currentThread():
+    """Return the current Thread object, corresponding to the caller's thread of control.
+
+    This function is deprecated, use current_thread() instead.
+
+    """
+    import warnings
+    warnings.warn('currentThread() is deprecated, use current_thread() instead',
+                  DeprecationWarning, stacklevel=2)
+    return current_thread()
+
+def active_count():
+    """Return the number of Thread objects currently alive.
+
+    The returned count is equal to the length of the list returned by
+    enumerate().
+
+    """
+    # NOTE: if the logic in here ever changes, update Modules/posixmodule.c
+    # warn_about_fork_with_threads() to match.
+    with _active_limbo_lock:
+        return len(_active) + len(_limbo)
+
+def activeCount():
+    """Return the number of Thread objects currently alive.
+
+    This function is deprecated, use active_count() instead.
+
+    """
+    import warnings
+    warnings.warn('activeCount() is deprecated, use active_count() instead',
+                  DeprecationWarning, stacklevel=2)
+    return active_count()
+
+def _enumerate():
+    # Same as enumerate(), but without the lock. Internal use only.
+    return list(_active.values()) + list(_limbo.values())
+
+def enumerate():
+    """Return a list of all Thread objects currently alive.
+
+    The list includes daemonic threads, dummy thread objects created by
+    current_thread(), and the main thread. It excludes terminated threads and
+    threads that have not yet been started.
+
+    """
+    with _active_limbo_lock:
+        return list(_active.values()) + list(_limbo.values())
+
+
+_threading_atexits = []
+_SHUTTING_DOWN = False
+
+def _register_atexit(func, *arg, **kwargs):
+    """CPython internal: register *func* to be called before joining threads.
+
+    The registered *func* is called with its arguments just before all
+    non-daemon threads are joined in `_shutdown()`. It provides a similar
+    purpose to `atexit.register()`, but its functions are called prior to
+    threading shutdown instead of interpreter shutdown.
+
+    For similarity to atexit, the registered functions are called in reverse.
+    """
+    if _SHUTTING_DOWN:
+        raise RuntimeError("can't register atexit after shutdown")
+
+    call = functools.partial(func, *arg, **kwargs)
+    _threading_atexits.append(call)
+
+
+from _thread import stack_size
+
+# Create the main thread object,
+# and make it available for the interpreter
+# (Py_Main) as threading._shutdown.
+
+_main_thread = _MainThread()
+
+def _shutdown():
+    """
+    Wait until the Python thread state of all non-daemon threads get deleted.
+    """
+    # Obscure:  other threads may be waiting to join _main_thread.  That's
+    # dubious, but some code does it.  We can't wait for C code to release
+    # the main thread's tstate_lock - that won't happen until the interpreter
+    # is nearly dead.  So we release it here.  Note that just calling _stop()
+    # isn't enough:  other threads may already be waiting on _tstate_lock.
+    if _main_thread._is_stopped and _is_main_interpreter():
+        # _shutdown() was already called
+        return
+
+    global _SHUTTING_DOWN
+    _SHUTTING_DOWN = True
+
+    # Call registered threading atexit functions before threads are joined.
+    # Order is reversed, similar to atexit.
+    for atexit_call in reversed(_threading_atexits):
+        atexit_call()
+
+    # Main thread
+    if _main_thread.ident == get_ident():
+        tlock = _main_thread._tstate_lock
+        # The main thread isn't finished yet, so its thread state lock can't
+        # have been released.
+        assert tlock is not None
+        assert tlock.locked()
+        tlock.release()
+        _main_thread._stop()
+    else:
+        # bpo-1596321: _shutdown() must be called in the main thread.
+        # If the threading module was not imported by the main thread,
+        # _main_thread is the thread which imported the threading module.
+        # In this case, ignore _main_thread, similar behavior than for threads
+        # spawned by C libraries or using _thread.start_new_thread().
+        pass
+
+    # Join all non-deamon threads
+    while True:
+        with _shutdown_locks_lock:
+            locks = list(_shutdown_locks)
+            _shutdown_locks.clear()
+
+        if not locks:
+            break
+
+        for lock in locks:
+            # mimic Thread.join()
+            lock.acquire()
+            lock.release()
+
+        # new threads can be spawned while we were waiting for the other
+        # threads to complete
+
+
+def main_thread():
+    """Return the main thread object.
+
+    In normal conditions, the main thread is the thread from which the
+    Python interpreter was started.
+    """
+    # XXX Figure this out for subinterpreters.  (See gh-75698.)
+    return _main_thread
+
+# get thread-local implementation, either from the thread
+# module, or from the python fallback
+
+try:
+    from _thread import _local as local
+except ImportError:
+    from _threading_local import local
+
+
+def _after_fork():
+    """
+    Cleanup threading module state that should not exist after a fork.
+    """
+    # Reset _active_limbo_lock, in case we forked while the lock was held
+    # by another (non-forked) thread.  http://bugs.python.org/issue874900
+    global _active_limbo_lock, _main_thread
+    global _shutdown_locks_lock, _shutdown_locks
+    _active_limbo_lock = RLock()
+
+    # fork() only copied the current thread; clear references to others.
+    new_active = {}
+
+    try:
+        current = _active[get_ident()]
+    except KeyError:
+        # fork() was called in a thread which was not spawned
+        # by threading.Thread. For example, a thread spawned
+        # by thread.start_new_thread().
+        current = _MainThread()
+
+    _main_thread = current
+
+    # reset _shutdown() locks: threads re-register their _tstate_lock below
+    _shutdown_locks_lock = _allocate_lock()
+    _shutdown_locks = set()
+
+    with _active_limbo_lock:
+        # Dangling thread instances must still have their locks reset,
+        # because someone may join() them.
+        threads = set(_enumerate())
+        threads.update(_dangling)
+        for thread in threads:
+            # Any lock/condition variable may be currently locked or in an
+            # invalid state, so we reinitialize them.
+            if thread is current:
+                # There is only one active thread. We reset the ident to
+                # its new value since it can have changed.
+                thread._reset_internal_locks(True)
+                ident = get_ident()
+                if isinstance(thread, _DummyThread):
+                    thread.__class__ = _MainThread
+                    thread._name = 'MainThread'
+                    thread._daemonic = False
+                    thread._set_tstate_lock()
+                thread._ident = ident
+                new_active[ident] = thread
+            else:
+                # All the others are already stopped.
+                thread._reset_internal_locks(False)
+                thread._stop()
+
+        _limbo.clear()
+        _active.clear()
+        _active.update(new_active)
+        assert len(_active) == 1
+
+
+if hasattr(_os, "register_at_fork"):
+    _os.register_at_fork(after_in_child=_after_fork)