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# -*- coding: utf-8 -*-
"""
lockfile.py - Platform-independent advisory file locks.
Requires Python 2.5 unless you apply 2.4.diff
Locking is done on a per-thread basis instead of a per-process basis.
Usage:
>>> lock = LockFile('somefile')
>>> try:
... lock.acquire()
... except AlreadyLocked:
... print 'somefile', 'is locked already.'
... except LockFailed:
... print 'somefile', 'can\\'t be locked.'
... else:
... print 'got lock'
got lock
>>> print lock.is_locked()
True
>>> lock.release()
>>> lock = LockFile('somefile')
>>> print lock.is_locked()
False
>>> with lock:
... print lock.is_locked()
True
>>> print lock.is_locked()
False
>>> lock = LockFile('somefile')
>>> # It is okay to lock twice from the same thread...
>>> with lock:
... lock.acquire()
...
>>> # Though no counter is kept, so you can't unlock multiple times...
>>> print lock.is_locked()
False
Exceptions:
Error - base class for other exceptions
LockError - base class for all locking exceptions
AlreadyLocked - Another thread or process already holds the lock
LockFailed - Lock failed for some other reason
UnlockError - base class for all unlocking exceptions
AlreadyUnlocked - File was not locked.
NotMyLock - File was locked but not by the current thread/process
"""
from __future__ import absolute_import
import functools
import os
import socket
import threading
import warnings
# Work with PEP8 and non-PEP8 versions of threading module.
if not hasattr(threading, "current_thread"):
threading.current_thread = threading.currentThread
if not hasattr(threading.Thread, "get_name"):
threading.Thread.get_name = threading.Thread.getName
__all__ = ['Error', 'LockError', 'LockTimeout', 'AlreadyLocked',
'LockFailed', 'UnlockError', 'NotLocked', 'NotMyLock',
'LinkFileLock', 'MkdirFileLock', 'SQLiteFileLock',
'LockBase', 'locked']
class Error(Exception):
"""
Base class for other exceptions.
>>> try:
... raise Error
... except Exception:
... pass
"""
pass
class LockError(Error):
"""
Base class for error arising from attempts to acquire the lock.
>>> try:
... raise LockError
... except Error:
... pass
"""
pass
class LockTimeout(LockError):
"""Raised when lock creation fails within a user-defined period of time.
>>> try:
... raise LockTimeout
... except LockError:
... pass
"""
pass
class AlreadyLocked(LockError):
"""Some other thread/process is locking the file.
>>> try:
... raise AlreadyLocked
... except LockError:
... pass
"""
pass
class LockFailed(LockError):
"""Lock file creation failed for some other reason.
>>> try:
... raise LockFailed
... except LockError:
... pass
"""
pass
class UnlockError(Error):
"""
Base class for errors arising from attempts to release the lock.
>>> try:
... raise UnlockError
... except Error:
... pass
"""
pass
class NotLocked(UnlockError):
"""Raised when an attempt is made to unlock an unlocked file.
>>> try:
... raise NotLocked
... except UnlockError:
... pass
"""
pass
class NotMyLock(UnlockError):
"""Raised when an attempt is made to unlock a file someone else locked.
>>> try:
... raise NotMyLock
... except UnlockError:
... pass
"""
pass
class _SharedBase(object):
def __init__(self, path):
self.path = path
def acquire(self, timeout=None):
"""
Acquire the lock.
* If timeout is omitted (or None), wait forever trying to lock the
file.
* If timeout > 0, try to acquire the lock for that many seconds. If
the lock period expires and the file is still locked, raise
LockTimeout.
* If timeout <= 0, raise AlreadyLocked immediately if the file is
already locked.
"""
raise NotImplemented("implement in subclass")
def release(self):
"""
Release the lock.
If the file is not locked, raise NotLocked.
"""
raise NotImplemented("implement in subclass")
def __enter__(self):
"""
Context manager support.
"""
self.acquire()
return self
def __exit__(self, *_exc):
"""
Context manager support.
"""
self.release()
def __repr__(self):
return "<%s: %r>" % (self.__class__.__name__, self.path)
class LockBase(_SharedBase):
"""Base class for platform-specific lock classes."""
def __init__(self, path, threaded=True, timeout=None):
"""
>>> lock = LockBase('somefile')
>>> lock = LockBase('somefile', threaded=False)
"""
super(LockBase, self).__init__(path)
self.lock_file = os.path.abspath(path) + ".lock"
self.hostname = socket.gethostname()
self.pid = os.getpid()
if threaded:
t = threading.current_thread()
# Thread objects in Python 2.4 and earlier do not have ident
# attrs. Worm around that.
ident = getattr(t, "ident", hash(t))
self.tname = "-%x" % (ident & 0xffffffff)
else:
self.tname = ""
dirname = os.path.dirname(self.lock_file)
# unique name is mostly about the current process, but must
# also contain the path -- otherwise, two adjacent locked
# files conflict (one file gets locked, creating lock-file and
# unique file, the other one gets locked, creating lock-file
# and overwriting the already existing lock-file, then one
# gets unlocked, deleting both lock-file and unique file,
# finally the last lock errors out upon releasing.
self.unique_name = os.path.join(dirname,
"%s%s.%s%s" % (self.hostname,
self.tname,
self.pid,
hash(self.path)))
self.timeout = timeout
def is_locked(self):
"""
Tell whether or not the file is locked.
"""
raise NotImplemented("implement in subclass")
def i_am_locking(self):
"""
Return True if this object is locking the file.
"""
raise NotImplemented("implement in subclass")
def break_lock(self):
"""
Remove a lock. Useful if a locking thread failed to unlock.
"""
raise NotImplemented("implement in subclass")
def __repr__(self):
return "<%s: %r -- %r>" % (self.__class__.__name__, self.unique_name,
self.path)
def _fl_helper(cls, mod, *args, **kwds):
warnings.warn("Import from %s module instead of lockfile package" % mod,
DeprecationWarning, stacklevel=2)
# This is a bit funky, but it's only for awhile. The way the unit tests
# are constructed this function winds up as an unbound method, so it
# actually takes three args, not two. We want to toss out self.
if not isinstance(args[0], str):
# We are testing, avoid the first arg
args = args[1:]
if len(args) == 1 and not kwds:
kwds["threaded"] = True
return cls(*args, **kwds)
def LinkFileLock(*args, **kwds):
"""Factory function provided for backwards compatibility.
Do not use in new code. Instead, import LinkLockFile from the
lockfile.linklockfile module.
"""
from . import linklockfile
return _fl_helper(linklockfile.LinkLockFile, "lockfile.linklockfile",
*args, **kwds)
def MkdirFileLock(*args, **kwds):
"""Factory function provided for backwards compatibility.
Do not use in new code. Instead, import MkdirLockFile from the
lockfile.mkdirlockfile module.
"""
from . import mkdirlockfile
return _fl_helper(mkdirlockfile.MkdirLockFile, "lockfile.mkdirlockfile",
*args, **kwds)
def SQLiteFileLock(*args, **kwds):
"""Factory function provided for backwards compatibility.
Do not use in new code. Instead, import SQLiteLockFile from the
lockfile.mkdirlockfile module.
"""
from . import sqlitelockfile
return _fl_helper(sqlitelockfile.SQLiteLockFile, "lockfile.sqlitelockfile",
*args, **kwds)
def locked(path, timeout=None):
"""Decorator which enables locks for decorated function.
Arguments:
- path: path for lockfile.
- timeout (optional): Timeout for acquiring lock.
Usage:
@locked('/var/run/myname', timeout=0)
def myname(...):
...
"""
def decor(func):
@functools.wraps(func)
def wrapper(*args, **kwargs):
lock = FileLock(path, timeout=timeout)
lock.acquire()
try:
return func(*args, **kwargs)
finally:
lock.release()
return wrapper
return decor
if hasattr(os, "link"):
from . import linklockfile as _llf
LockFile = _llf.LinkLockFile
else:
from . import mkdirlockfile as _mlf
LockFile = _mlf.MkdirLockFile
FileLock = LockFile
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