This module provides a way to create a mutex which is valid for the system (i.e.: it can be seen by multiple processes).
Note that the mutex is kept until release_mutex() is called or when it's garbage-collected.
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#
# Copyright: Brainwy Software
'''
To use, create a SystemMutex, check if it was acquired (get_mutex_aquired()) and if acquired the
mutex is kept until the instance is collected or release_mutex is called.
I.e.:
mutex = SystemMutex('my_unique_name')
if mutex.get_mutex_aquired():
print('acquired')
else:
print('not acquired')
'''
import re
import sys
import tempfile
import traceback
import weakref
# Note: Null comes from http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/68205
NULL = Null()
def check_valid_mutex_name(mutex_name):
# To be windows/linux compatible we can't use non-valid filesystem names
# (as on linux it's a file-based lock).
regexp = re.compile(r'[\*\?"<>|/\\:]')
result = regexp.findall(mutex_name)
if result is not None and len(result) > 0:
raise AssertionError('Mutex name is invalid: %s' % (mutex_name,))
if sys.platform == 'win32':
import os
class SystemMutex(object):
def __init__(self, mutex_name):
check_valid_mutex_name(mutex_name)
filename = os.path.join(tempfile.gettempdir(), mutex_name)
try:
os.unlink(filename)
except:
pass
try:
handle = os.open(filename, os.O_CREAT | os.O_EXCL | os.O_RDWR)
try:
try:
pid = str(os.getpid())
except:
pid = 'unable to get pid'
os.write(handle, pid)
except:
pass # Ignore this as it's pretty much optional
except:
self._release_mutex = NULL
self._acquired = False
else:
def release_mutex(*args, **kwargs):
# Note: can't use self here!
if not getattr(release_mutex, 'called', False):
release_mutex.called = True
try:
os.close(handle)
except:
traceback.print_exc()
try:
# Removing is optional as we'll try to remove on startup anyways (but
# let's do it to keep the filesystem cleaner).
os.unlink(filename)
except:
pass
# Don't use __del__: this approach doesn't have as many pitfalls.
self._ref = weakref.ref(self, release_mutex)
self._release_mutex = release_mutex
self._acquired = True
def get_mutex_aquired(self):
return self._acquired
def release_mutex(self):
self._release_mutex()
# Below we have a better implementation, but it relies on win32api which we can't be sure
# the client will have available in the Python version installed at the client, so, we're
# using a file-based implementation which should work in any implementation.
#
# from win32api import CloseHandle, GetLastError
# from win32event import CreateMutex
# from winerror import ERROR_ALREADY_EXISTS
#
# class SystemMutex(object):
#
# def __init__(self, mutex_name):
# check_valid_mutex_name(mutex_name)
# mutex = self.mutex = CreateMutex(None, False, mutex_name)
# self._acquired = GetLastError() != ERROR_ALREADY_EXISTS
#
# if self._acquired:
#
# def release_mutex(*args, **kwargs):
# Note: can't use self here!
# if not getattr(release_mutex, 'called', False):
# release_mutex.called = True
# try:
# CloseHandle(mutex)
# except:
# traceback.print_exc()
#
# Don't use __del__: this approach doesn't have as many pitfalls.
# self._ref = weakref.ref(self, release_mutex)
# self._release_mutex = release_mutex
# else:
# self._release_mutex = NULL
# CloseHandle(mutex)
#
# def get_mutex_aquired(self):
# return self._acquired
#
# def release_mutex(self):
# self._release_mutex()
else: # Linux
import os
import fcntl
class SystemMutex(object):
def __init__(self, mutex_name):
check_valid_mutex_name(mutex_name)
filename = os.path.join(tempfile.gettempdir(), mutex_name)
try:
handle = open(filename, 'w')
fcntl.flock(handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
except:
self._release_mutex = NULL
self._acquired = False
try:
handle.close()
except:
pass
else:
def release_mutex(*args, **kwargs):
# Note: can't use self here!
if not getattr(release_mutex, 'called', False):
release_mutex.called = True
try:
fcntl.flock(handle, fcntl.LOCK_UN)
except:
traceback.print_exc()
try:
handle.close()
except:
traceback.print_exc()
try:
# Removing is pretty much optional (but let's do it to keep the
# filesystem cleaner).
os.unlink(filename)
except:
pass
# Don't use __del__: this approach doesn't have as many pitfalls.
self._ref = weakref.ref(self, release_mutex)
self._release_mutex = release_mutex
self._acquired = True
def get_mutex_aquired(self):
return self._acquired
def release_mutex(self):
self._release_mutex()
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