GHUM wrote:
> hello,
>
> in my application I am using
>
> hSem = win32event.CreateSemaphore (None, 1,
> 1,"stringincludinginterfaceandport")
> rt=win32event.WaitForSingleObject (hSem, 0)
> if rt != win32event.WAIT_TIMEOUT:
> really_do_start_my_app()
> else:
> print "application allready running"
>
> to make sure that only ONE instance of the application is running at a
> time. (as it implements a local webserver, that is necessary. Two
> webservers listening on one port is bad)
>
> Now I am going to make this application run on Linux. How can I get
> similiar behaviour on Linux?
>
> I know of the .pid files that get written by some server processes ...
> BUT they do not get cleaned up on unclean shutdown of the application.
>
> is there some better method?
>
> Or some module which wraps the details of .pid-files quite nicely?
> (like "trying to remove to check if other instance is still
> running...., failing properly on missing write privs etc.)
You might consider using a cooperative file locking for that. I do this as
follows:
#-------------------------------------------------------------------------------
class LockFileCreationException(Exception):
pass
#-------------------------------------------------------------------------------
class LockObtainException(Exception):
pass
#-------------------------------------------------------------------------------
class LockFile(object):
def __init__(self, name, fail_on_lock=False, cleanup=True):
self.name = name
self.cleanup = cleanup
try:
self.fd = os.open(name, os.O_WRONLY | os.O_CREAT | os.O_APPEND)
except OSError, e:
if e[0] == 2:
raise LockFileCreationException()
self.file = os.fdopen(self.fd, "w")
lock_flags = fcntl.LOCK_EX
if fail_on_lock:
lock_flags |= fcntl.LOCK_NB
try:
fcntl.flock(self.file, lock_flags)
except IOError, e:
if e[0] == 11:
raise LockObtainException()
raise
def __enter__(self):
return self.file
def __exit__(self, unused_exc_type, unused_exc_val, unused_exc_tb):
self.file.close()
# we are told to cleanup after ourselves,
# however it might be that another process
# has done so - so we don't fail in that
# case.
if self.cleanup:
try:
os.remove(self.name)
except OSError, e:
if not e[0] == 2:
raise
You can use the LockFile as context, and either block until the lock is
released (which is most probably not what you want), or fail with
LockObtainException.
Diez
--
http://mail.python.org/mailman/listinfo/python-list
