/usr/share/pyshared/beaker/synchronization.py is in python-beaker 1.6.3-1.1.
This file is owned by root:root, with mode 0o644.
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File- and mutex-based mutual exclusion synchronizers are provided,
as well as a name-based mutex which locks within an application
based on a string name.
"""
import os
import sys
import tempfile
try:
import threading as _threading
except ImportError:
import dummy_threading as _threading
# check for fcntl module
try:
sys.getwindowsversion()
has_flock = False
except:
try:
import fcntl
has_flock = True
except ImportError:
has_flock = False
from beaker import util
from beaker.exceptions import LockError
__all__ = ["file_synchronizer", "mutex_synchronizer", "null_synchronizer",
"NameLock", "_threading"]
class NameLock(object):
"""a proxy for an RLock object that is stored in a name based
registry.
Multiple threads can get a reference to the same RLock based on the
name alone, and synchronize operations related to that name.
"""
locks = util.WeakValuedRegistry()
class NLContainer(object):
def __init__(self, reentrant):
if reentrant:
self.lock = _threading.RLock()
else:
self.lock = _threading.Lock()
def __call__(self):
return self.lock
def __init__(self, identifier = None, reentrant = False):
if identifier is None:
self._lock = NameLock.NLContainer(reentrant)
else:
self._lock = NameLock.locks.get(identifier, NameLock.NLContainer,
reentrant)
def acquire(self, wait = True):
return self._lock().acquire(wait)
def release(self):
self._lock().release()
_synchronizers = util.WeakValuedRegistry()
def _synchronizer(identifier, cls, **kwargs):
return _synchronizers.sync_get((identifier, cls), cls, identifier, **kwargs)
def file_synchronizer(identifier, **kwargs):
if not has_flock or 'lock_dir' not in kwargs:
return mutex_synchronizer(identifier)
else:
return _synchronizer(identifier, FileSynchronizer, **kwargs)
def mutex_synchronizer(identifier, **kwargs):
return _synchronizer(identifier, ConditionSynchronizer, **kwargs)
class null_synchronizer(object):
"""A 'null' synchronizer, which provides the :class:`.SynchronizerImpl` interface
without any locking.
"""
def acquire_write_lock(self, wait=True):
return True
def acquire_read_lock(self):
pass
def release_write_lock(self):
pass
def release_read_lock(self):
pass
acquire = acquire_write_lock
release = release_write_lock
class SynchronizerImpl(object):
"""Base class for a synchronization object that allows
multiple readers, single writers.
"""
def __init__(self):
self._state = util.ThreadLocal()
class SyncState(object):
__slots__ = 'reentrantcount', 'writing', 'reading'
def __init__(self):
self.reentrantcount = 0
self.writing = False
self.reading = False
def state(self):
if not self._state.has():
state = SynchronizerImpl.SyncState()
self._state.put(state)
return state
else:
return self._state.get()
state = property(state)
def release_read_lock(self):
state = self.state
if state.writing:
raise LockError("lock is in writing state")
if not state.reading:
raise LockError("lock is not in reading state")
if state.reentrantcount == 1:
self.do_release_read_lock()
state.reading = False
state.reentrantcount -= 1
def acquire_read_lock(self, wait = True):
state = self.state
if state.writing:
raise LockError("lock is in writing state")
if state.reentrantcount == 0:
x = self.do_acquire_read_lock(wait)
if (wait or x):
state.reentrantcount += 1
state.reading = True
return x
elif state.reading:
state.reentrantcount += 1
return True
def release_write_lock(self):
state = self.state
if state.reading:
raise LockError("lock is in reading state")
if not state.writing:
raise LockError("lock is not in writing state")
if state.reentrantcount == 1:
self.do_release_write_lock()
state.writing = False
state.reentrantcount -= 1
release = release_write_lock
def acquire_write_lock(self, wait = True):
state = self.state
if state.reading:
raise LockError("lock is in reading state")
if state.reentrantcount == 0:
x = self.do_acquire_write_lock(wait)
if (wait or x):
state.reentrantcount += 1
state.writing = True
return x
elif state.writing:
state.reentrantcount += 1
return True
acquire = acquire_write_lock
def do_release_read_lock(self):
raise NotImplementedError()
def do_acquire_read_lock(self):
raise NotImplementedError()
def do_release_write_lock(self):
raise NotImplementedError()
def do_acquire_write_lock(self):
raise NotImplementedError()
class FileSynchronizer(SynchronizerImpl):
"""A synchronizer which locks using flock().
"""
def __init__(self, identifier, lock_dir):
super(FileSynchronizer, self).__init__()
self._filedescriptor = util.ThreadLocal()
if lock_dir is None:
lock_dir = tempfile.gettempdir()
else:
lock_dir = lock_dir
self.filename = util.encoded_path(
lock_dir,
[identifier],
extension='.lock'
)
def _filedesc(self):
return self._filedescriptor.get()
_filedesc = property(_filedesc)
def _open(self, mode):
filedescriptor = self._filedesc
if filedescriptor is None:
filedescriptor = os.open(self.filename, mode)
self._filedescriptor.put(filedescriptor)
return filedescriptor
def do_acquire_read_lock(self, wait):
filedescriptor = self._open(os.O_CREAT | os.O_RDONLY)
if not wait:
try:
fcntl.flock(filedescriptor, fcntl.LOCK_SH | fcntl.LOCK_NB)
return True
except IOError:
os.close(filedescriptor)
self._filedescriptor.remove()
return False
else:
fcntl.flock(filedescriptor, fcntl.LOCK_SH)
return True
def do_acquire_write_lock(self, wait):
filedescriptor = self._open(os.O_CREAT | os.O_WRONLY)
if not wait:
try:
fcntl.flock(filedescriptor, fcntl.LOCK_EX | fcntl.LOCK_NB)
return True
except IOError:
os.close(filedescriptor)
self._filedescriptor.remove()
return False
else:
fcntl.flock(filedescriptor, fcntl.LOCK_EX)
return True
def do_release_read_lock(self):
self._release_all_locks()
def do_release_write_lock(self):
self._release_all_locks()
def _release_all_locks(self):
filedescriptor = self._filedesc
if filedescriptor is not None:
fcntl.flock(filedescriptor, fcntl.LOCK_UN)
os.close(filedescriptor)
self._filedescriptor.remove()
class ConditionSynchronizer(SynchronizerImpl):
"""a synchronizer using a Condition."""
def __init__(self, identifier):
super(ConditionSynchronizer, self).__init__()
# counts how many asynchronous methods are executing
self.async = 0
# pointer to thread that is the current sync operation
self.current_sync_operation = None
# condition object to lock on
self.condition = _threading.Condition(_threading.Lock())
def do_acquire_read_lock(self, wait = True):
self.condition.acquire()
try:
# see if a synchronous operation is waiting to start
# or is already running, in which case we wait (or just
# give up and return)
if wait:
while self.current_sync_operation is not None:
self.condition.wait()
else:
if self.current_sync_operation is not None:
return False
self.async += 1
finally:
self.condition.release()
if not wait:
return True
def do_release_read_lock(self):
self.condition.acquire()
try:
self.async -= 1
# check if we are the last asynchronous reader thread
# out the door.
if self.async == 0:
# yes. so if a sync operation is waiting, notifyAll to wake
# it up
if self.current_sync_operation is not None:
self.condition.notifyAll()
elif self.async < 0:
raise LockError("Synchronizer error - too many "
"release_read_locks called")
finally:
self.condition.release()
def do_acquire_write_lock(self, wait = True):
self.condition.acquire()
try:
# here, we are not a synchronous reader, and after returning,
# assuming waiting or immediate availability, we will be.
if wait:
# if another sync is working, wait
while self.current_sync_operation is not None:
self.condition.wait()
else:
# if another sync is working,
# we dont want to wait, so forget it
if self.current_sync_operation is not None:
return False
# establish ourselves as the current sync
# this indicates to other read/write operations
# that they should wait until this is None again
self.current_sync_operation = _threading.currentThread()
# now wait again for asyncs to finish
if self.async > 0:
if wait:
# wait
self.condition.wait()
else:
# we dont want to wait, so forget it
self.current_sync_operation = None
return False
finally:
self.condition.release()
if not wait:
return True
def do_release_write_lock(self):
self.condition.acquire()
try:
if self.current_sync_operation is not _threading.currentThread():
raise LockError("Synchronizer error - current thread doesnt "
"have the write lock")
# reset the current sync operation so
# another can get it
self.current_sync_operation = None
# tell everyone to get ready
self.condition.notifyAll()
finally:
# everyone go !!
self.condition.release()
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