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|
"""
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 = FileLock('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 = FileLock('somefile')
>>> print lock.is_locked()
False
>>> with lock:
... print lock.is_locked()
True
>>> print lock.is_locked()
False
>>> # 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 division
import sys
import socket
import os
import threading
import time
import errno
# Work with PEP8 and non-PEP8 versions of threading module.
try:
threading.current_thread
except AttributeError:
threading.current_thread = threading.currentThread
try:
# python 2.6 has threading.current_thread so we need to do this separately.
threading.Thread.get_name
except AttributeError:
threading.Thread.get_name = threading.Thread.getName
__all__ = ['Error', 'LockError', 'LockTimeout', 'AlreadyLocked',
'LockFailed', 'UnlockError', 'NotLocked', 'NotMyLock',
'LinkFileLock', 'MkdirFileLock', 'SQLiteFileLock']
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 LockBase:
"""Base class for platform-specific lock classes."""
def __init__(self, path, threaded=True):
"""
>>> lock = LockBase('somefile')
>>> lock = LockBase('somefile', threaded=False)
"""
self.path = path
self.lock_file = os.path.abspath(path) + '.lock'
self.hostname = socket.gethostname()
self.pid = os.getpid()
if threaded:
tname = '%s-' % threading.current_thread().get_name()
else:
tname = ''
dirname = os.path.dirname(self.lock_file)
self.unique_name = os.path.join(dirname,
'%s.%s%s' % (self.hostname,
tname,
self.pid))
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 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 __enter__(self):
"""Context manager support."""
self.acquire()
return self
def __exit__(self, *_exc):
"""Context manager support."""
self.release()
class LinkFileLock(LockBase):
"""Lock access to a file using atomic property of link(2)."""
def acquire(self, timeout=None):
try:
open(self.unique_name, 'wb').close()
except IOError:
raise LockFailed
end_time = time.time()
if timeout is not None and timeout > 0:
end_time += timeout
while True:
# Try and create a hard link to it.
try:
os.link(self.unique_name, self.lock_file)
except OSError:
# Link creation failed. Maybe we've double-locked?
nlinks = os.stat(self.unique_name).st_nlink
if nlinks == 2:
# The original link plus the one I created == 2. We're
# good to go.
return
else:
# Otherwise the lock creation failed.
if timeout is not None and time.time() > end_time:
os.unlink(self.unique_name)
if timeout > 0:
raise LockTimeout
else:
raise AlreadyLocked
time.sleep(timeout is not None and timeout / 10 or 0.1)
else:
# Link creation succeeded. We're good to go.
return
def release(self):
if not self.is_locked():
raise NotLocked
elif not os.path.exists(self.unique_name):
raise NotMyLock
os.unlink(self.unique_name)
os.unlink(self.lock_file)
def is_locked(self):
return os.path.exists(self.lock_file)
def i_am_locking(self):
return (self.is_locked() and
os.path.exists(self.unique_name) and
os.stat(self.unique_name).st_nlink == 2)
def break_lock(self):
if os.path.exists(self.lock_file):
os.unlink(self.lock_file)
class MkdirFileLock(LockBase):
"""Lock file by creating a directory."""
def __init__(self, path, threaded=True):
"""
>>> lock = MkdirFileLock('somefile')
>>> lock = MkdirFileLock('somefile', threaded=False)
"""
LockBase.__init__(self, path, threaded)
if threaded:
tname = '%x-' % thread.get_ident()
else:
tname = ''
# Lock file itself is a directory. Place the unique file name into
# it.
self.unique_name = os.path.join(self.lock_file,
'%s.%s%s' % (self.hostname,
tname,
self.pid))
def acquire(self, timeout=None):
end_time = time.time()
if timeout is not None and timeout > 0:
end_time += timeout
if timeout is None:
wait = 0.1
else:
wait = max(0, timeout / 10)
while True:
try:
os.mkdir(self.lock_file)
except OSError:
err = sys.exc_info()[1]
if err.errno == errno.EEXIST:
# Already locked.
if os.path.exists(self.unique_name):
# Already locked by me.
return
if timeout is not None and time.time() > end_time:
if timeout > 0:
raise LockTimeout
else:
# Someone else has the lock.
raise AlreadyLocked
time.sleep(wait)
else:
# Couldn't create the lock for some other reason
raise LockFailed
else:
open(self.unique_name, 'wb').close()
return
def release(self):
if not self.is_locked():
raise NotLocked
elif not os.path.exists(self.unique_name):
raise NotMyLock
os.unlink(self.unique_name)
os.rmdir(self.lock_file)
def is_locked(self):
return os.path.exists(self.lock_file)
def i_am_locking(self):
return (self.is_locked() and
os.path.exists(self.unique_name))
def break_lock(self):
if os.path.exists(self.lock_file):
for name in os.listdir(self.lock_file):
os.unlink(os.path.join(self.lock_file, name))
os.rmdir(self.lock_file)
class SQLiteFileLock(LockBase):
'Demonstration of using same SQL-based locking.'
import tempfile
_fd, testdb = tempfile.mkstemp()
os.close(_fd)
os.unlink(testdb)
del _fd, tempfile
def __init__(self, path, threaded=True):
LockBase.__init__(self, path, threaded)
self.lock_file = unicode(self.lock_file)
self.unique_name = unicode(self.unique_name)
import sqlite3
self.connection = sqlite3.connect(SQLiteFileLock.testdb)
c = self.connection.cursor()
try:
c.execute('create table locks'
'('
' lock_file varchar(32),'
' unique_name varchar(32)'
')')
except sqlite3.OperationalError:
pass
else:
self.connection.commit()
import atexit
atexit.register(os.unlink, SQLiteFileLock.testdb)
def acquire(self, timeout=None):
end_time = time.time()
if timeout is not None and timeout > 0:
end_time += timeout
if timeout is None:
wait = 0.1
elif timeout <= 0:
wait = 0
else:
wait = timeout / 10
cursor = self.connection.cursor()
while True:
if not self.is_locked():
# Not locked. Try to lock it.
cursor.execute('insert into locks'
' (lock_file, unique_name)'
' values'
' (?, ?)',
(self.lock_file, self.unique_name))
self.connection.commit()
# Check to see if we are the only lock holder.
cursor.execute('select * from locks'
' where unique_name = ?',
(self.unique_name,))
rows = cursor.fetchall()
if len(rows) > 1:
# Nope. Someone else got there. Remove our lock.
cursor.execute('delete from locks'
' where unique_name = ?',
(self.unique_name,))
self.connection.commit()
else:
# Yup. We're done, so go home.
return
else:
# Check to see if we are the only lock holder.
cursor.execute('select * from locks'
' where unique_name = ?',
(self.unique_name,))
rows = cursor.fetchall()
if len(rows) == 1:
# We're the locker, so go home.
return
# Maybe we should wait a bit longer.
if timeout is not None and time.time() > end_time:
if timeout > 0:
# No more waiting.
raise LockTimeout
else:
# Someone else has the lock and we are impatient..
raise AlreadyLocked
# Well, okay. We'll give it a bit longer.
time.sleep(wait)
def release(self):
if not self.is_locked():
raise NotLocked
if not self.i_am_locking():
raise NotMyLock((self._who_is_locking(), self.unique_name))
cursor = self.connection.cursor()
cursor.execute('delete from locks'
' where unique_name = ?',
(self.unique_name,))
self.connection.commit()
def _who_is_locking(self):
cursor = self.connection.cursor()
cursor.execute('select unique_name from locks'
' where lock_file = ?',
(self.lock_file,))
return cursor.fetchone()[0]
def is_locked(self):
cursor = self.connection.cursor()
cursor.execute('select * from locks'
' where lock_file = ?',
(self.lock_file,))
rows = cursor.fetchall()
return not not rows
def i_am_locking(self):
cursor = self.connection.cursor()
cursor.execute('select * from locks'
' where lock_file = ?'
' and unique_name = ?',
(self.lock_file, self.unique_name))
return not not cursor.fetchall()
def break_lock(self):
cursor = self.connection.cursor()
cursor.execute('delete from locks'
' where lock_file = ?',
(self.lock_file,))
self.connection.commit()
if hasattr(os, 'link'):
FileLock = LinkFileLock
else:
FileLock = MkdirFileLock
|