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#!/usr/bin/env python
# -*- coding: latin1 -*-
#----------------------------------------------------------------------------
# glock.py: Global mutex
#
# See __doc__ string below.
#
# Requires:
# - Python 1.5.2 or newer (www.python.org)
# - On windows: win32 extensions installed
# (http://www.python.org/windows/win32all/win32all.exe)
# - OS: Unix, Windows.
#
# $Id: //depot/rgutils/rgutils/glock.py#5 $
#----------------------------------------------------------------------------
'''
This module defines the class GlobalLock that implements a global
(inter-process) mutex on Windows and Unix, using file-locking on
Unix.
@see: class L{GlobalLock} for more details.
'''
__version__ = '0.2.' + '$Revision: #5 $'[12:-2]
__author__ = 'Richard Gruet', 'rjgruet@yahoo.com'
__date__ = '$Date: 2005/06/19 $'[7:-2], '$Author: rgruet $'[9:-2]
__since__ = '2000-01-22'
__doc__ += '\n@author: %s (U{%s})\n@version: %s' % (__author__[0],
__author__[1], __version__)
__all__ = ['GlobalLock', 'GlobalLockError', 'LockAlreadyAcquired', 'NotOwner']
# Imports:
import sys, string, os, errno, re
# System-dependent imports for locking implementation:
_windows = (sys.platform == 'win32')
if _windows:
try:
import win32event, win32api, pywintypes
except ImportError:
sys.stderr.write('The win32 extensions need to be installed!')
try:
import ctypes
except ImportError:
ctypes = None
else: # assume Unix
try:
import fcntl
except ImportError:
sys.stderr.write("On what kind of OS am I ? (Mac?) I should be on "
"Unix but can't import fcntl.\n")
raise
import threading
# Exceptions :
# ----------
class GlobalLockError(Exception):
''' Error raised by the glock module.
'''
pass
class NotOwner(GlobalLockError):
''' Attempt to release somebody else's lock.
'''
pass
class LockAlreadyAcquired(GlobalLockError):
''' Non-blocking acquire but lock already seized.
'''
pass
# Constants
# ---------:
if sys.version[:3] < '2.2':
True, False = 1, 0 # built-in in Python 2.2+
#----------------------------------------------------------------------------
class GlobalLock:
#----------------------------------------------------------------------------
''' A global mutex.
B{Specification}
- The lock must act as a global mutex, ie block between different
candidate processus, but ALSO between different candidate
threads of the same process.
- It must NOT block in case of reentrant lock request issued by
the SAME thread.
- Extraneous unlocks should be ideally harmless.
B{Implementation}
In Python there is no portable global lock AFAIK. There is only a
LOCAL/ in-process Lock mechanism (threading.RLock), so we have to
implement our own solution:
- Unix: use fcntl.flock(). Recursive calls OK. Different process OK.
But <> threads, same process don't block so we have to use an extra
threading.RLock to fix that point.
- Windows: We use WIN32 mutex from Python Win32 extensions. Can't use
std module msvcrt.locking(), because global lock is OK, but
blocks also for 2 calls from the same thread!
'''
RE_ERROR_MSG = re.compile ("^\[Errno ([0-9]+)\]")
def __init__(self, fpath, lockInitially=False, logger=None):
''' Creates (or opens) a global lock.
@param fpath: Path of the file used as lock target. This is also
the global id of the lock. The file will be created
if non existent.
@param lockInitially: if True locks initially.
@param logger: an optional logger object.
'''
self.logger = logger
self.fpath = fpath
if os.path.exists(fpath):
self.previous_lockfile_present = True
else:
self.previous_lockfile_present = False
if _windows:
self.name = string.replace(fpath, '\\', '_')
self.mutex = win32event.CreateMutex(None, lockInitially, self.name)
else: # Unix
self.name = fpath
self.flock = open(fpath, 'w')
self.fdlock = self.flock.fileno()
self.threadLock = threading.RLock()
if lockInitially:
self.acquire()
def __del__(self):
#print '__del__ called' ##
try: self.release()
except: pass
if _windows:
win32api.CloseHandle(self.mutex)
else:
try: self.flock.close()
except: pass
def __repr__(self):
return '<Global lock @ %s>' % self.name
def acquire(self, blocking=False):
""" Locks. Attemps to acquire a lock.
@param blocking: If True, suspends caller until done. Otherwise,
LockAlreadyAcquired is raised if the lock cannot be acquired immediately.
On windows an IOError is always raised after ~10 sec if the lock
can't be acquired.
@exception GlobalLockError: if lock can't be acquired (timeout)
@exception LockAlreadyAcquired: someone already has the lock and
the caller decided not to block.
"""
if self.logger:
self.logger.info('Creating lockfile: %s', self.fpath)
if _windows:
if blocking:
timeout = win32event.INFINITE
else:
timeout = 0
r = win32event.WaitForSingleObject(self.mutex, timeout)
if r == win32event.WAIT_FAILED:
raise GlobalLockError("Can't acquire mutex: error")
if not blocking and r == win32event.WAIT_TIMEOUT:
raise LockAlreadyAcquired('Lock %s already acquired by '
'someone else' % self.name)
else:
# First, acquire the global (inter-process) lock:
if blocking:
options = fcntl.LOCK_EX
else:
options = fcntl.LOCK_EX|fcntl.LOCK_NB
try:
fcntl.flock(self.fdlock, options)
except IOError, message: #(errno 13: perm. denied,
# 36: Resource deadlock avoided)
if not blocking and self._errnoOf (message) == errno.EWOULDBLOCK:
raise LockAlreadyAcquired('Lock %s already acquired by '
'someone else' % self.name)
else:
raise GlobalLockError('Cannot acquire lock on "file" '
'%s: %s\n' % (self.name, message))
#print 'got file lock.' ##
# Then acquire the local (inter-thread) lock:
if not self.threadLock.acquire(blocking):
fcntl.flock(self.fdlock, fcntl.LOCK_UN) # release global lock
raise LockAlreadyAcquired('Lock %s already acquired by '
'someone else' % self.name)
if self.previous_lockfile_present and self.logger:
self.logger.warn("Stale lockfile detected and claimed.")
#print 'got thread lock.' ##
self.is_locked = True
def release(self, skip_delete=False):
''' Unlocks. (caller must own the lock!)
@param skip_delete: don't try to delete the file. This can
be used when the original filename has changed; for
instance, if the lockfile is erased out-of-band, or if
the directory it contains has been renamed.
@return: The lock count.
@exception IOError: if file lock can't be released
@exception NotOwner: Attempt to release somebody else's lock.
'''
if not self.is_locked:
return
if not skip_delete:
if self.logger:
self.logger.debug('Removing lock file: %s', self.fpath)
os.unlink(self.fpath)
elif self.logger:
# At certain times the lockfile will have been removed or
# moved away before we call release(); log a message because
# this is unusual and could be an error.
self.logger.debug('Oops, my lock file disappeared: %s', self.fpath)
if _windows:
if ctypes:
result = ctypes.windll.kernel32.ReleaseMutex(self.mutex.handle)
if not result:
raise NotOwner("Attempt to release somebody else's lock")
else:
try:
win32event.ReleaseMutex(self.mutex)
#print "released mutex"
except pywintypes.error, e:
errCode, fctName, errMsg = e.args
if errCode == 288:
raise NotOwner("Attempt to release somebody else's lock")
else:
raise GlobalLockError('%s: err#%d: %s' % (fctName, errCode,
errMsg))
else:
# First release the local (inter-thread) lock:
try:
self.threadLock.release()
except AssertionError:
raise NotOwner("Attempt to release somebody else's lock")
# Then release the global (inter-process) lock:
try:
fcntl.flock(self.fdlock, fcntl.LOCK_UN)
except IOError: # (errno 13: permission denied)
raise GlobalLockError('Unlock of file "%s" failed\n' %
self.name)
self.is_locked = False
def _errnoOf (self, message):
match = self.RE_ERROR_MSG.search(str(message))
if match:
return int(match.group(1))
else:
raise Exception ('Malformed error message "%s"' % message)
#----------------------------------------------------------------------------
def test():
#----------------------------------------------------------------------------
##TODO: a more serious test with distinct processes !
print 'Testing glock.py...'
# unfortunately can't test inter-process lock here!
lockName = 'myFirstLock'
l = GlobalLock(lockName)
if not _windows:
assert os.path.exists(lockName)
l.acquire()
l.acquire() # reentrant lock, must not block
l.release()
l.release()
try: l.release()
except NotOwner: pass
else: raise Exception('should have raised a NotOwner exception')
# Check that <> threads of same process do block:
import threading, time
thread = threading.Thread(target=threadMain, args=(l,))
print 'main: locking...',
l.acquire()
print ' done.'
thread.start()
time.sleep(3)
print '\nmain: unlocking...',
l.release()
print ' done.'
time.sleep(0.1)
print '=> Test of glock.py passed.'
return l
def threadMain(lock):
print 'thread started(%s).' % lock
try: lock.acquire(blocking=False)
except LockAlreadyAcquired: pass
else: raise Exception('should have raised LockAlreadyAcquired')
print 'thread: locking (should stay blocked for ~ 3 sec)...',
lock.acquire()
print 'thread: locking done.'
print 'thread: unlocking...',
lock.release()
print ' done.'
print 'thread ended.'
#----------------------------------------------------------------------------
# M A I N
#----------------------------------------------------------------------------
if __name__ == "__main__":
l = test()
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