diff options
Diffstat (limited to 'notification/lockfile.py')
| -rw-r--r-- | notification/lockfile.py | 500 |
1 files changed, 500 insertions, 0 deletions
diff --git a/notification/lockfile.py b/notification/lockfile.py new file mode 100644 index 00000000..d1707030 --- /dev/null +++ b/notification/lockfile.py @@ -0,0 +1,500 @@ + +""" +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 |