I've made a simple lock mechanism. I believe this lock mechanism should
work both on Windows and Linux (I've only tested on Linux and only on a
local filesystem). I'll test it in windows and shared filesystems later.
2012/3/1 Jaap Karssenberg <jaap.karssenb...@gmail.com>
> On Thu, Mar 1, 2012 at 11:01 AM, João Santos <j...@jsantos.eu> wrote:
>
>> Wouldn't this module: http://packages.python.org/lockfile/lockfile.htmldo
>> the job?
>>
>
> Afraid not. This module will do locking between multiple processes on the
> same system, but it is not suitable for .e.g. multiple systems accessing
> the same share drive.
>
> I think the most important use case for this multi-user sharing is each
> user having his or her own computer, but sharing a share drive.
>
> So locking needs to be platform independent, and can only use the (shared)
> file system.
>
> Regards,
>
> Jaap
>
>
import os
import uuid
import shutil
class LockFailedError(Exception):
pass
class NotMyLockError(Exception):
pass
class CrossLock(object):
def __init__(self, name):
"""Represents a lockfile with a name"""
self.lock = ".{0}.lock".format(name)
#We will have a unique id to assure that the lock
#belongs to the instance
self.id = uuid.uuid1()
self.filename = "{0}/{1}".format(self.lock, self.id)
def _create_lockfile(self):
"""Creates the lock dir and file"""
#mkdir is atomic on windows and linux
#and will fail if dir already exists
os.mkdir(self.lock)
os.mknod(self.filename)
def acquire(self):
"""Tries to acquire lock."""
try:
self._create_lockfile()
except:
raise LockFailedError
def break_lock(self):
"""Removes the lock directory"""
shutil.rmtree(self.lock)
def is_locked(self):
"""Tests if the file is locked"""
return os.access(self.lock, os.F_OK)
def is_my_lock(self):
"""Tests if the lock belongs to the instance"""
return os.access(self.filename, os.F_OK)
def release(self):
"""Removes the lock but only if owned by the instance"""
if not self.is_my_lock():
raise NotMyLockError
else:
self.break_lock()
if __name__ == '__main__':
lock = CrossLock("teste")
lock2 = CrossLock("teste")
print "Trying to get get lock"
try:
lock.acquire()
print "Correct (Succeeded)"
except:
print "Incorrect (Failed)"
print "Trying to get a lock again"
try:
lock.acquire()
print "Incorrect (Succeeded)"
except:
print "Correct (Failed)"
print "Trying to release the lock with the wrong instance"
try:
lock2.release()
print "Incorrect (Succeeded)"
except:
print "Correct (Failed)"
print "Tryng to release the lock with the correct instance"
try:
lock.release()
print "Correct (Succeeded)"
except:
print "Incorrect (Failed)"
raise
print "Testing if it's locked"
if lock.is_locked():
print "Incorrect (True)"
else:
print "Correct (False)"
print "Trying to get get lock again"
try:
lock.acquire()
print "Correct (Succeeded)"
except:
print "Incorrect (Failed)"
print "Testing if it's locked"
if lock.is_locked():
print "Correct (True)"
else:
print "Incorrect (False)"
print "Trying to break the lock"
try:
lock2.break_lock()
print "Correct (Succeeded)"
except:
print "Incorrect (Failed)"
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