cpython/Lib/threading.py

961 lines
31 KiB
Python

"""Thread module emulating a subset of Java's threading model."""
import sys as _sys
import _thread
from time import sleep as _sleep
try:
from time import monotonic as _time
except ModuleNotFoundError:
from time import time as _time
from traceback import format_exc as _format_exc
from _weakrefset import WeakSet
from itertools import islice as _islice
try:
from _collections import deque as _deque
except ModuleNotFoundError:
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 originaly 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
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):
global _profile_hook
_profile_hook = func
def settrace(func):
global _trace_hook
_trace_hook = func
# Synchronization classes
Lock = _allocate_lock
def RLock(*args, **kwargs):
if _CRLock is None:
return _PyRLock(*args, **kwargs)
return _CRLock(*args, **kwargs)
class _RLock:
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):
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):
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:
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):
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()
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)
if not gotit:
try:
self._waiters.remove(waiter)
except ValueError:
pass
return gotit
finally:
self._acquire_restore(saved_state)
def wait_for(self, predicate, timeout=None):
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):
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):
self.notify(len(self._waiters))
notifyAll = notify_all
class Semaphore:
# 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):
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):
with self._cond:
self._value += 1
self._cond.notify()
def __exit__(self, t, v, tb):
self.release()
class BoundedSemaphore(Semaphore):
"""Semaphore that checks that # releases is <= # acquires"""
def __init__(self, value=1):
Semaphore.__init__(self, value)
self._initial_value = value
def release(self):
if self._value >= self._initial_value:
raise ValueError("Semaphore released too many times")
return Semaphore.release(self)
class Event:
# 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__()
def is_set(self):
return self._flag
isSet = is_set
def set(self):
self._cond.acquire()
try:
self._flag = True
self._cond.notify_all()
finally:
self._cond.release()
def clear(self):
self._cond.acquire()
try:
self._flag = False
finally:
self._cond.release()
def wait(self, timeout=None):
self._cond.acquire()
try:
signaled = self._flag
if not signaled:
signaled = self._cond.wait(timeout)
return signaled
finally:
self._cond.release()
# 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:
"""
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 that are 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 = 0
def _newname(template="Thread-%d"):
global _counter
_counter += 1
return template % _counter
# Active thread administration
_active_limbo_lock = _allocate_lock()
_active = {} # maps thread id to Thread object
_limbo = {}
# For debug and leak testing
_dangling = WeakSet()
# Main class for threads
class Thread:
__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):
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._started = Event()
self._stopped = False
self._block = Condition(Lock())
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
_dangling.add(self)
def _reset_internal_locks(self):
# private! Called by _after_fork() to reset our internal locks as
# they may be in an invalid state leading to a deadlock or crash.
if hasattr(self, '_block'): # DummyThread deletes _block
self._block.__init__()
self._started._reset_internal_locks()
def __repr__(self):
assert self._initialized, "Thread.__init__() was not called"
status = "initial"
if self._started.is_set():
status = "started"
if self._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):
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):
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 _bootstrap_inner(self):
try:
self._set_ident()
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:
_sys.stderr.write("Exception in thread %s:\n%s\n" %
(self.name, _format_exc()))
else:
# 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:
self._stop()
try:
# We don't call self._delete() because it also
# grabs _active_limbo_lock.
del _active[get_ident()]
except:
pass
def _stop(self):
self._block.acquire()
self._stopped = True
self._block.notify_all()
self._block.release()
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
# it gets a KeyError if another Thread instance was created.
#
# This all means that KeyError from trying to delete something from
# _active if dummy_threading is being used is a red herring. But
# since it isn't if dummy_threading is *not* being used then don't
# hide the exception.
try:
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.
except KeyError:
if 'dummy_threading' not in _sys.modules:
raise
def join(self, timeout=None):
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")
self._block.acquire()
try:
if timeout is None:
while not self._stopped:
self._block.wait()
else:
deadline = _time() + timeout
while not self._stopped:
delay = deadline - _time()
if delay <= 0:
break
self._block.wait(delay)
finally:
self._block.release()
@property
def name(self):
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):
assert self._initialized, "Thread.__init__() not called"
return self._ident
def is_alive(self):
assert self._initialized, "Thread.__init__() not called"
return self._started.is_set() and not self._stopped
isAlive = is_alive
@property
def daemon(self):
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
# This is garbage collected through an exit handler
class _MainThread(Thread):
def __init__(self):
Thread.__init__(self, name="MainThread", daemon=False)
self._started.set()
self._set_ident()
with _active_limbo_lock:
_active[self._ident] = self
def _exitfunc(self):
self._stop()
t = _pickSomeNonDaemonThread()
while t:
t.join()
t = _pickSomeNonDaemonThread()
self._delete()
def _pickSomeNonDaemonThread():
for t in enumerate():
if not t.daemon and t.is_alive():
return t
return None
# 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)
# Thread._block consumes an OS-level locking primitive, which
# can never be used by a _DummyThread. Since a _DummyThread
# instance is immortal, that's bad, so release this resource.
del self._block
self._started.set()
self._set_ident()
with _active_limbo_lock:
_active[self._ident] = self
def _stop(self):
pass
def join(self, timeout=None):
assert False, "cannot join a dummy thread"
# Global API functions
def current_thread():
try:
return _active[get_ident()]
except KeyError:
return _DummyThread()
currentThread = current_thread
def active_count():
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():
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.
_shutdown = _MainThread()._exitfunc
# get thread-local implementation, either from the thread
# module, or from the python fallback
try:
from _thread import _local as local
except ModuleNotFoundError:
from _threading_local import local
def _after_fork():
# This function is called by Python/ceval.c:PyEval_ReInitThreads which
# is called from PyOS_AfterFork. Here we 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
_active_limbo_lock = _allocate_lock()
# fork() only copied the current thread; clear references to others.
new_active = {}
current = current_thread()
with _active_limbo_lock:
for thread in _active.values():
# Any lock/condition variable may be currently locked or in an
# invalid state, so we reinitialize them.
thread._reset_internal_locks()
if thread is current:
# There is only one active thread. We reset the ident to
# its new value since it can have changed.
ident = get_ident()
thread._ident = ident
new_active[ident] = thread
else:
# All the others are already stopped.
thread._stop()
_limbo.clear()
_active.clear()
_active.update(new_active)
assert len(_active) == 1