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# Copyright (c) 2009-2012 Denis Bilenko. See LICENSE for details.
"""Locking primitives"""
from __future__ import absolute_import
from gevent.hub import getcurrent
from gevent._compat import PYPY
from gevent._semaphore import Semaphore, BoundedSemaphore # pylint:disable=no-name-in-module,import-error
__all__ = [
'Semaphore',
'DummySemaphore',
'BoundedSemaphore',
'RLock',
]
# On PyPy, we don't compile the Semaphore class with Cython. Under
# Cython, each individual method holds the GIL for its entire
# duration, ensuring that no other thread can interrupt us in an
# unsafe state (only when we _do_wait do we call back into Python and
# allow switching threads). Simulate that here through the use of a manual
# lock. (We use a separate lock for each semaphore to allow sys.settrace functions
# to use locks *other* than the one being traced.)
if PYPY:
# TODO: Need to use monkey.get_original?
try:
from _thread import allocate_lock as _allocate_lock # pylint:disable=import-error,useless-suppression
from _thread import get_ident as _get_ident # pylint:disable=import-error,useless-suppression
except ImportError:
# Python 2
from thread import allocate_lock as _allocate_lock # pylint:disable=import-error,useless-suppression
from thread import get_ident as _get_ident # pylint:disable=import-error,useless-suppression
_sem_lock = _allocate_lock()
def untraceable(f):
# Don't allow re-entry to these functions in a single thread, as can
# happen if a sys.settrace is used
def wrapper(self):
me = _get_ident()
try:
count = self._locking[me]
except KeyError:
count = self._locking[me] = 1
else:
count = self._locking[me] = count + 1
if count:
return
try:
return f(self)
finally:
count = count - 1
if not count:
del self._locking[me]
else:
self._locking[me] = count
return wrapper
class _OwnedLock(object):
def __init__(self):
self._owner = None
self._block = _allocate_lock()
self._locking = {}
self._count = 0
@untraceable
def acquire(self):
me = _get_ident()
if self._owner == me:
self._count += 1
return
self._owner = me
self._block.acquire()
self._count = 1
@untraceable
def release(self):
self._count = count = self._count - 1
if not count:
self._block.release()
self._owner = None
# acquire, wait, and release all acquire the lock on entry and release it
# on exit. acquire and wait can call _do_wait, which must release it on entry
# and re-acquire it for them on exit.
class _around(object):
__slots__ = ('before', 'after')
def __init__(self, before, after):
self.before = before
self.after = after
def __enter__(self):
self.before()
def __exit__(self, t, v, tb):
self.after()
def _decorate(func, cmname):
# functools.wrap?
def wrapped(self, *args, **kwargs):
with getattr(self, cmname):
return func(self, *args, **kwargs)
return wrapped
Semaphore._py3k_acquire = Semaphore.acquire = _decorate(Semaphore.acquire, '_lock_locked')
Semaphore.release = _decorate(Semaphore.release, '_lock_locked')
Semaphore.wait = _decorate(Semaphore.wait, '_lock_locked')
Semaphore._do_wait = _decorate(Semaphore._do_wait, '_lock_unlocked')
_Sem_init = Semaphore.__init__
def __init__(self, *args, **kwargs):
l = self._lock_lock = _OwnedLock()
self._lock_locked = _around(l.acquire, l.release)
self._lock_unlocked = _around(l.release, l.acquire)
_Sem_init(self, *args, **kwargs)
Semaphore.__init__ = __init__
del _decorate
del untraceable
class DummySemaphore(object):
"""
DummySemaphore(value=None) -> DummySemaphore
A Semaphore initialized with "infinite" initial value. None of its
methods ever block.
This can be used to parameterize on whether or not to actually
guard access to a potentially limited resource. If the resource is
actually limited, such as a fixed-size thread pool, use a real
:class:`Semaphore`, but if the resource is unbounded, use an
instance of this class. In that way none of the supporting code
needs to change.
Similarly, it can be used to parameterize on whether or not to
enforce mutual exclusion to some underlying object. If the
underlying object is known to be thread-safe itself mutual
exclusion is not needed and a ``DummySemaphore`` can be used, but
if that's not true, use a real ``Semaphore``.
"""
# Internally this is used for exactly the purpose described in the
# documentation. gevent.pool.Pool uses it instead of a Semaphore
# when the pool size is unlimited, and
# gevent.fileobject.FileObjectThread takes a parameter that
# determines whether it should lock around IO to the underlying
# file object.
def __init__(self, value=None):
"""
.. versionchanged:: 1.1rc3
Accept and ignore a *value* argument for compatibility with Semaphore.
"""
pass
def __str__(self):
return '<%s>' % self.__class__.__name__
def locked(self):
"""A DummySemaphore is never locked so this always returns False."""
return False
def release(self):
"""Releasing a dummy semaphore does nothing."""
pass
def rawlink(self, callback):
# XXX should still work and notify?
pass
def unlink(self, callback):
pass
def wait(self, timeout=None):
"""Waiting for a DummySemaphore returns immediately."""
pass
def acquire(self, blocking=True, timeout=None):
"""
A DummySemaphore can always be acquired immediately so this always
returns True and ignores its arguments.
.. versionchanged:: 1.1a1
Always return *true*.
"""
# pylint:disable=unused-argument
return True
def __enter__(self):
pass
def __exit__(self, typ, val, tb):
pass
class RLock(object):
"""
A mutex that can be acquired more than once by the same greenlet.
"""
def __init__(self):
self._block = Semaphore(1)
self._owner = None
self._count = 0
def __repr__(self):
return "<%s at 0x%x _block=%s _count=%r _owner=%r)>" % (
self.__class__.__name__,
id(self),
self._block,
self._count,
self._owner)
def acquire(self, blocking=1):
me = getcurrent()
if self._owner is me:
self._count = self._count + 1
return 1
rc = self._block.acquire(blocking)
if rc:
self._owner = me
self._count = 1
return rc
def __enter__(self):
return self.acquire()
def release(self):
if self._owner is not getcurrent():
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, typ, value, tb):
self.release()
# Internal methods used by condition variables
def _acquire_restore(self, count_owner):
count, owner = count_owner
self._block.acquire()
self._count = count
self._owner = owner
def _release_save(self):
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 is getcurrent()
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