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

import sys as _sys

import _thread

try:

from time import monotonic as _time

except ImportError:

from time import time 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__ = ['active_count', 'Condition', 'current_thread', 'enumerate', 'Event',

'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Thread', 'Barrier',

'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 owner=%r count=%d>" % (

self.__class__.__name__, owner, self._count)

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 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 uses 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 relased. 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()

# 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()

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=self._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)

# 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

def _delete(self):

"Remove current thread from the dict of currently running threads."

# Notes about running with _dummy_thread:

#

# Must take care to not raise an exception if _dummy_thread is being

# used (and thus this module is being used as an instance of

# dummy_threading). _dummy_thread.get_ident() always returns -1 since

# there is only one thread if _dummy_thread is being used. Thus

# len(_active) is always <= 1 here, and any Thread instance created

# overwrites the (if any) thread currently registered in _active.

#

# An instance of _MainThread is always created by 'threading'. This

# gets overwritten the instant an instance of Thread is created; both

# threads return -1 from _dummy_thread.get_ident() and thus have the

# same key in the dict. So when the _MainThread instance created by

# 'threading' tries to clean itself up when atexit calls this method