"""
Implementation of the standard :mod:`threading` using greenlets.
.. note::
This module is a helper for :mod:`gevent.monkey` and is not
intended to be used directly. For spawning greenlets in your
applications, prefer higher level constructs like
:class:`gevent.Greenlet` class or :func:`gevent.spawn`. Attributes
in this module like ``__threading__`` are implementation artifacts subject
to change at any time.
.. versionchanged:: 1.2.3
Defer adjusting the stdlib's list of active threads until we are
monkey patched. Previously this was done at import time. We are
documented to only be used as a helper for monkey patching, so this should
functionally be the same, but some applications ignore the documentation and
directly import this module anyway.
A positive consequence is that ``import gevent.threading,
threading; threading.current_thread()`` will no longer return a DummyThread
before monkey-patching.
"""
import os
import sys
__implements__ = [
'local',
'_allocate_lock',
'Lock',
'_get_ident',
'_sleep',
'_DummyThread',
# RLock cannot go here, even though we need to import it.
# If it goes here, it replaces the RLock from the native
# threading module, but we really just need it here when some
# things import this module.
#'RLock',
] + ([
'_start_new_thread',
] if sys.version_info[:2] < (3, 13) else [
'_start_joinable_thread',
'_ThreadHandle',
'_make_thread_handle',
])
__extensions__ = [
]
import threading as __threading__ # imports os, sys, _thread, functools, time, itertools
_DummyThread_ = __threading__._DummyThread
_MainThread_ = __threading__._MainThread
from gevent.local import local
from gevent.thread import start_new_thread as _start_new_thread
from gevent.thread import start_joinable_thread
from gevent.thread import _ThreadHandle
from gevent.thread import _make_thread_handle
from gevent.thread import allocate_lock as _allocate_lock
from gevent.thread import get_ident as _get_ident
from gevent.hub import sleep as _sleep, getcurrent
from gevent.lock import RLock
from gevent._util import LazyOnClass
# Exports, prevent unused import warnings.
# XXX: Why don't we use __all__?
local = local
start_new_thread = _start_new_thread
_start_joinable_thread = start_joinable_thread
_make_thread_handle = _make_thread_handle
_ThreadHandle = _ThreadHandle
allocate_lock = _allocate_lock
_get_ident = _get_ident
_sleep = _sleep
getcurrent = getcurrent
Lock = _allocate_lock
RLock = RLock
def _cleanup(g):
__threading__._active.pop(_get_ident(g), None)
def _make_cleanup_id(gid):
def _(_r):
__threading__._active.pop(gid, None)
return _
_weakref = None
class _DummyThread(_DummyThread_):
# We avoid calling the superclass constructor. This makes us about
# twice as fast:
#
# - 1.16 vs 0.68usec on PyPy (unknown version, older Intel mac)
# - 29.3 vs 17.7usec on CPython 2.7 (older intel Mac)
# - 0.98 vs 2.95usec on CPython 3.12.2 (newer M2 mac)
#
# It als has the important effect of avoiding allocation and then
# immediate deletion of _Thread__block, a lock. This is especially
# important on PyPy where locks go through the cpyext API and
# Cython, which is known to be slow and potentially buggy (e.g.,
# https://bitbucket.org/pypy/pypy/issues/2149/memory-leak-for-python-subclass-of-cpyext#comment-22347393)
# These objects are constructed quite frequently in some cases, so
# the optimization matters: for example, in gunicorn, which uses
# pywsgi.WSGIServer, most every request is handled in a new greenlet,
# and every request uses a logging.Logger to write the access log,
# and every call to a log method captures the current thread (by
# default).
#
# (Obviously we have to duplicate the effects of the constructor,
# at least for external state purposes, which is potentially
# slightly fragile.)
# For the same reason, instances of this class will cleanup their own entry
# in ``threading._active``
# This class also solves a problem forking process with subprocess: after forking,
# Thread.__stop is called, which throws an exception when __block doesn't
# exist.
# Capture the static things as class vars to save on memory/
# construction time.
# In Py2, they're all private; in Py3, they become protected
_Thread__stopped = _is_stopped = _stopped = False
_Thread__initialized = _initialized = True
_Thread__daemonic = _daemonic = True
_Thread__args = _args = ()
_Thread__kwargs = _kwargs = None
_Thread__target = _target = None
_Thread_ident = _ident = None
_Thread__started = _started = __threading__.Event()
_Thread__started.set()
_tstate_lock = None
_handle = None # 3.13
def __init__(self): # pylint:disable=super-init-not-called
#_DummyThread_.__init__(self)
# It'd be nice to use a pattern like "greenlet-%d", but there are definitely
# third-party libraries checking thread names to detect DummyThread objects.
self._name = self._Thread__name = __threading__._newname("Dummy-%d")
# All dummy threads in the same native thread share the same ident
# (that of the native thread), unless we're monkey-patched.
self._set_ident()
# _handle is only needed for 3.13; keeps a weak reference
# to the greenlet.
self._handle = _make_thread_handle(self._ident)
# ``_native_id`` backs the ``native_id`` property,
# when available.
try:
self._native_id = __threading__.get_native_id()
except AttributeError: # pragma: no cover
pass
g = getcurrent()
gid = _get_ident(g)
__threading__._active[gid] = self
rawlink = getattr(g, 'rawlink', None)
if rawlink is not None:
# raw greenlet.greenlet greenlets don't
# have rawlink...
rawlink(_cleanup)
else:
# ... so for them we use weakrefs.
# See https://github.com/gevent/gevent/issues/918
ref = self.__weakref_ref
ref = ref(g, _make_cleanup_id(gid)) # pylint:disable=too-many-function-args
self.__raw_ref = ref
assert self.__raw_ref is ref # prevent pylint thinking its unused
def _Thread__stop(self):
pass
_stop = _Thread__stop # py3
def _wait_for_tstate_lock(self, *args, **kwargs): # pylint:disable=signature-differs
pass
@LazyOnClass
def __weakref_ref(self):
return __import__('weakref').ref
# In Python 3.11.8+ and 3.12.2+ (yes, minor patch releases),
# CPython's ``threading._after_fork`` hook began swizzling the
# type of the _DummyThread into _MainThread if such a dummy thread
# was the current thread when ``os.fork()`` gets called.
# From CPython's perspective, that's a more-or-less fine thing to do.
# While _DummyThread isn't a subclass of _MainThread, they are both
# subclasses of Thread, and _MainThread doesn't add any new instance
# variables.
#
# From gevent's perspective, that's NOT good. Our _DummyThread
# doesn't have all the instance variables that Thread does, and so
# attempting to do anything with this now-fake _MainThread doesn't work.
# You in fact immediately get assertion errors from inside ``_after_fork``.
# Now, these are basically harmless --- they're printed, and they prevent the cleanup
# of some globals in _threading, but that probably doesn't matter --- but
# people complained, and it could break some test scenarios (due to unexpected
# output on stderr, for example)
#
# We thought of a few options to patch around this:
#
# - Live with the performance penalty. Newer CPythons are making it
# harder and harder to perform well, so if we can possibly avoid
# adding our own performance regressions, that would be good.
#
# - ``after_fork`` uses ``isinstance(current, _DummyThread)``
# before swizzling, so we could use a metaclass to make that
# check return false. That's a fairly large compatibility risk,
# both because of the use of a metaclass (what if some other
# subclass of _DummyTHread is using an incompatible metaclass?)
# and the change in ``isinstance`` behaviour. We could limit the latter
# to a window around the fork, using ``os.register_at_fork(before, after_in_parent=)``,
# but that's a lot of moving pieces requiring the use of a global or class
# variable to track state.
#
# - We could copy the ivars of the current main thread into the
# _DummyThread in ``register_at_fork(before=)``. That appears to
# work, but also requires the use of
# ``register_at_fork(after_in_parent=)`` to reverse it.
#
# - We could simply prevent swizzling the class in the first
# place. In combination with
# ``register_at_fork(after_in_child=)`` to establish a *real*
# new _MainThread, that's a clean solution. Establishing a real
# new _MainThread is something that CPython itself is prepared
# to do if it can't figure out what the current thread is. The
# compatibility risk of this is relatively low: swizzling
# classes is frowned upon and uncommon, and we can limit it to
# just preventing this specific case. And if somebody was
# attempting this already with some other thread subclass, it
# would (probably?) have the exact same issues, so we can be pretty
# sure nobody is doing that.
#
# We're initially going with the last fix; the __class__ part is here,
# the ``after_in_child`` fixup we only apply if we're monkey-patching.
#
# Now, all of this is moot in 3.13, which takes a very different
# approach to handling this, and also changes some names. See
# https://github.com/python/cpython/commit/0e9c364f4ac18a2237bdbac702b96bcf8ef9cb09
# Tests pass just fine in 3.8 (and presumably 3.9 and 3.10) with these fixes
# applied, but just in case, we only do it where we know it's necessary.
_NEEDS_CLASS_FORK_FIXUP = (
(sys.version_info[:2] == (3, 11) and sys.version_info[:3] >= (3, 11, 8))
or sys.version_info[:3] >= (3, 12, 2)
)
if _NEEDS_CLASS_FORK_FIXUP:
# Override with a property, as opposed to using __setattr__,
# to avoid adding overhead on any other attribute setting.
@property
def __class__(self):
return type(self)
@__class__.setter
def __class__(self, new_class):
# Even if we wanted to allow setting this, I'm not sure
# exactly how to do so when we have a property object handling it.
# Getting the descriptor from ``object.__dict__['__class__']``
# and using its ``__set__`` method raises a TypeError (as does
# the simpler ``super().__class__``).
#
# Better allow the TypeError for now as opposed to silently ignoring
# the assignment.
if new_class is not _MainThread_:
object.__dict__['__class__'].__set__(self, new_class)
def main_native_thread():
return __threading__.main_thread() # pylint:disable=no-member
# XXX: Issue 18808 breaks us on Python 3.4+.
# Thread objects now expect a callback from the interpreter itself
# (threadmodule.c:release_sentinel) when the C-level PyThreadState
# object is being deallocated. Because this never happens
# when a greenlet exits, join() and friends will block forever.
# Fortunately this is easy to fix: just ensure that the allocation of the
# lock, _set_sentinel, creates a *gevent* lock, and release it when
# we're done. The main _shutdown code is in Python and deals with
# this gracefully.
[docs]
class Thread(__threading__.Thread):
# Only happens in < 3.13
def _set_tstate_lock(self):
super(Thread, self)._set_tstate_lock()
greenlet = getcurrent()
greenlet.rawlink(self.__greenlet_finished)
def __greenlet_finished(self, _):
if self._tstate_lock:
self._tstate_lock.release()
self._stop()
__implements__.append('Thread')
[docs]
class Timer(Thread, __threading__.Timer): # pylint:disable=abstract-method,inherit-non-class
pass
__implements__.append('Timer')
_set_sentinel = allocate_lock
if sys.version_info[:2] < (3, 13):
__implements__.append('_set_sentinel')
else:
__extensions__.append('_set_sentinel')
# The main thread is patched up with more care
# in _gevent_will_monkey_patch
__implements__.remove('_get_ident')
__implements__.append('get_ident')
get_ident = _get_ident
__implements__.remove('_sleep')
if hasattr(__threading__, '_CRLock'):
# Python 3 changed the implementation of threading.RLock
# Previously it was a factory function around threading._RLock
# which in turn used _allocate_lock. Now, it wants to use
# threading._CRLock, which is imported from _thread.RLock and as such
# is implemented in C. So it bypasses our _allocate_lock function.
# Fortunately they left the Python fallback in place and use it
# if the imported _CRLock is None; this arranges for that to be the case.
# This was also backported to PyPy 2.7-7.0
_CRLock = None
__implements__.append('_CRLock')
class _ForkHooks:
_before_fork_current_thread = None
_before_fork_active = None
def before_fork_in_parent(self):
self._before_fork_active = dict(__threading__._active)
self._before_fork_current_thread = __threading__.current_thread()
def after_fork_in_child(self):
# We've already imported threading, which installed its "after" hook,
# so we're going to be called after that hook.
# Note that this is only installed when monkey-patching.
# TODO: Is there any point to checking to see if the current thread is
# our dummy thread before doing this?
active = __threading__._active
assert len(active) == 1
# We cannot actually kill the greenlets via throw():
# - If it was the main greenlet, the process will exit
# - In any case, that would unwind the stack and execute
# code that, before 2024-10-03, would never have executed.
#
# But we can take them out of the map and make them appear
# stopped; if they truly are no longer referenced, GC will
# kick in a nd delete the greenlet. If gevent is still waiting
# to switch to them, that will still happen...
#
# This happens automatically on <= 3.12 which hardcodes the call to
# ``Thread._stop``; for 3.13, we need to go through the handle.
current_ident = get_ident()
for green_ident, thread in self._before_fork_active.items():
if green_ident != current_ident:
try:
handle = thread._handle
except AttributeError:
assert sys.version_info[:2] < (3, 13)
assert not thread.is_alive()
else:
# We DO NOT want to bounce to the hub. We're running
# at a very sensitive time and it's best to keep tight control
# over what gets to run.
handle._set_done(enter_hub=False)
main = __threading__._MainThread()
main._ident = get_ident() # 3.13: reset to the greenlet version.
__threading__._active[__threading__.get_ident()] = main
__threading__._main_thread = main
main = __threading__.main_thread()
# XXX: Not the case. Maybe don't save main.
assert main.ident == __threading__.get_ident()
_fork_hooks = _ForkHooks()
def _gevent_will_monkey_patch(native_module, items, warn): # pylint:disable=unused-argument
# Make sure the MainThread can be found by our current greenlet ID,
# otherwise we get a new DummyThread, which cannot be joined.
# Fixes tests in test_threading_2 under PyPy.
main_thread = main_native_thread()
if __threading__.current_thread() != main_thread:
warn("Monkey-patching outside the main native thread. Some APIs "
"will not be available. Expect a KeyError to be printed at shutdown.")
return
if _get_ident() not in __threading__._active:
main_id = main_thread.ident
del __threading__._active[main_id]
main_thread._ident = main_thread._Thread__ident = _get_ident()
__threading__._active[_get_ident()] = main_thread
register_at_fork = getattr(os, 'register_at_fork', None)
if register_at_fork:
#if _DummyThread._NEEDS_CLASS_FORK_FIXUP:
register_at_fork(
before=_fork_hooks.before_fork_in_parent,
after_in_child=_fork_hooks.after_fork_in_child)