Jon Ribbens <jon+use...@unequivocal.eu>:
> On 2017-04-20, Cameron Simpson <c...@zip.com.au> wrote:
>> For myself, I like mkdir. It is portable. It is atomic. It fails if
>> the target exists. It works over NFS etc. It is easy.
>>
>> os.mkdir('lock')
>> ... do stuff ...
>> os.rmdir('lock')
>
> One downside to this is that if the process that 'holds the lock' dies
> before it reaches the 'rmdir' then the lock becomes wedged. With the
> 'flock' method, the operating system will automatically undo the lock.
> Of course, depending on your application, it's possible that this
> 'downside' may be a feature.
Combining both:
==Begin flock.py========================================================
"""File locking for Linux, Unix and Windows
Usage:
with FLock(pathname):
# critical section
where pathname refers to an existing, readable file.
On Windows, FLock creates a magic directory pathname.6e35b8cda6902579
upon locking and removes it upon unlocking. If the operating system
crashes or the Python process is killed ungracefully, the lock directory
could be left behind and would have to be removed manually.
"""
import os
if os.name == 'posix':
import fcntl
class FLock:
def __init__(self, pathname):
self.f = open(pathname)
def __enter__(self):
self.lock()
return None
def __exit__(self, exc_type, exc_value, traceback):
self.unlock()
return False
def lock(self):
fcntl.flock(self.f, fcntl.LOCK_EX)
def unlock(self):
self.f.close()
else:
import time
class FLock:
def __init__(self, pathname):
self.pathname = pathname + ".6e35b8cda6902579"
def __enter__(self):
self.lock()
return None
def __exit__(self, exc_type, exc_value, traceback):
self.unlock()
return False
def lock(self):
while True:
try:
os.mkdir(self.pathname)
return
except OSError:
time.sleep(1)
def unlock(self):
os.rmdir(self.pathname)
==end flock.py==========================================================
Marko
--
https://mail.python.org/mailman/listinfo/python-list
