# Source code for threading

    """Thread module emulating a subset of Java's threading model."""

    import os as _os
    import sys as _sys
    import _thread

    from time import monotonic as _time
    from traceback import format_exc as _format_exc
    from _weakrefset import WeakSet
    from itertools import islice as _islice, 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']

    # Rename some stuff so "from threading import *" is safe
    _start_new_thread = _thread.start_new_thread
    _allocate_lock = _thread.allocate_lock
    _set_sentinel = _thread._set_sentinel
    get_ident = _thread.get_ident
    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 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

    # 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 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()

    _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().
            try:
                self._release_save = lock._release_save
            except AttributeError:
                pass
            try:
                self._acquire_restore = lock._acquire_restore
            except AttributeError:
                pass
            try:
                self._is_owned = lock._is_owned
            except AttributeError:
                pass
            self._waiters = _deque()

        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(0):
                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")
            all_waiters = self._waiters
            waiters_to_notify = _deque(_islice(all_waiters, n))
            if not waiters_to_notify:
                return
            for waiter in waiters_to_notify:
                waiter.release()
                try:
                    all_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))

        notifyAll = 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 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):
            """Release a semaphore, incrementing the internal counter by one.

            When the counter is zero on entry and another thread is waiting for it
            to become larger than zero again, wake up that thread.

            """
            with self._cond:
                self._value += 1
                self._cond.notify()

        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):
            Semaphore.__init__(self, value)
            self._initial_value = value

        def release(self):
            """Release a semaphore, incrementing the internal counter by one.

            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.

            """
            with self._cond:
                if self._value >= self._initial_value:
                    raise ValueError("Semaphore released too many times")
                self._value += 1
                self._cond.notify()

    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 _reset_internal_locks(self):
            # private!  called by Thread._reset_internal_locks by _after_fork()
            self._cond.__init__(Lock())

        def is_set(self):
            """Return true if and only if the internal flag is true."""
            return self._flag

        isSet = 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 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().__next__
    _counter() # Consume 0 so first non-main thread has id 1.
    def _newname(template="Thread-%d"):
        return template % _counter()

    # Active thread administration
    _active_limbo_lock = _allocate_lock()
    _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()

    # 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
        # Need to store a reference to sys.exc_info for printing
        # out exceptions when a thread tries to use a global var. during interp.
        # shutdown and thus raises an exception about trying to perform some
        # operation on/with a NoneType
        _exc_info = _sys.exc_info
        # Keep sys.exc_clear too to clear the exception just before
        # allowing .join() to return.
        #XXX __exc_clear = _sys.exc_clear

        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 the argument tuple 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 = {}
            self._target = target
            self._name = str(name or _newname())
            self._args = args
            self._kwargs = kwargs
            if daemon is not None:
                self._daemonic = daemon
            else:
                self._daemonic = current_thread().daemon
            self._ident = None
            self._tstate_lock = None
            self._started = Event()
            self._is_stopped = False
            self._initialized = True
            # sys.stderr is not stored in the class like
            # sys.exc_info since it can be changed between instances
            self._stderr = _sys.stderr
            # 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._reset_internal_locks()
            if is_alive:
                self._set_tstate_lock()
            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:
                    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()

        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:
                    _shutdown_locks.add(self._tstate_lock)

        def _bootstrap_inner(self):
            try:
                self._set_ident()
                self._set_tstate_lock()
                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 SystemExit:
                    pass
                except:
                    # If sys.stderr is no more (most likely from interpreter
                    # shutdown) use self._stderr.  Otherwise still use sys (as in
                    # _sys) in case sys.stderr was redefined since the creation of
                    # self.
                    if _sys and _sys.stderr is not None:
                        print("Exception in thread %s:\n%s" %
                              (self.name, _format_exc()), file=_sys.stderr)
                    elif self._stderr is not None:
                        # Do the best job possible w/o a huge amt. of code to
                        # approximate a traceback (code ideas from
                        # Lib/traceback.py)
                        exc_type, exc_value, exc_tb = self._exc_info()
                        try:
                            print((
                                "Exception in thread " + self.name +
                                " (most likely raised during interpreter shutdown):"), file=self._stderr)
                            print((
                                "Traceback (most recent call last):"), file=self._stderr)
                            while exc_tb:
                                print((
                                    '  File "%s", line %s, in %s' %
                                    (exc_tb.tb_frame.f_code.co_filename,
                                        exc_tb.tb_lineno,
                                        exc_tb.tb_frame.f_code.co_name)), file=self._stderr)
                                exc_tb = exc_tb.tb_next
                            print(("%s: %s" % (exc_type, exc_value)), file=self._stderr)
                            self._stderr.flush()
                        # Make sure that exc_tb gets deleted since it is a memory
                        # hog; deleting everything else is just for thoroughness
                        finally:
                            del exc_type, exc_value, exc_tb
                finally:
                    # Prevent a race in
                    # test_threading.test_no_refcycle_through_target when
                    # the exception keeps the target alive past when we
                    # assert that it's dead.
                    #XXX self._exc_clear()
                    pass
            finally:
                with _active_limbo_lock:
                    try:
                        # We don't call self._delete() because it also
                        # grabs _active_limbo_lock.
                        del _active[get_ident()]
                    except:
                        pass

        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:
                    _shutdown_locks.discard(lock)

        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
            elif lock.acquire(block, timeout):
                lock.release()
                self._stop()

        @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

        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. The module function enumerate()
            returns a list of all alive threads.

            """
            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

        def isAlive(self):
            """Return whether the thread is alive.

            This method is deprecated, use is_alive() instead.
            """
            import warnings
            warnings.warn('isAlive() is deprecated, use is_alive() instead',
                          PendingDeprecationWarning, stacklevel=2)
            return self.is_alive()

        @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 self._started.is_set():
                raise RuntimeError("cannot set daemon status of active thread")
            self._daemonic = daemonic

        def isDaemon(self):
            return self.daemon

        def setDaemon(self, daemonic):
            self.daemon = daemonic

        def getName(self):
            return self.name

        def setName(self, name):
            self.name = name

    # 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()
            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=True)

            self._started.set()
            self._set_ident()
            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()

    currentThread = 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().

        """
        with _active_limbo_lock:
            return len(_active) + len(_limbo)

    activeCount = 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())

    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:
            # _shutdown() was already called
            return

        # Main thread
        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()

        # 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:
                # mimick 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.
        """
        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 = _allocate_lock()

        # fork() only copied the current thread; clear references to others.
        new_active = {}
        current = current_thread()
        _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()
                    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)