name : sqlitelockfile.py from __future__ import absolute_import, division import time import os try: unicode except NameError: unicode = str from . import LockBase, NotLocked, NotMyLock, LockTimeout, AlreadyLocked class SQLiteLockFile(LockBase): "Demonstrate SQL-based locking." testdb = None def __init__(self, path, threaded=True, timeout=None): """ >>> lock = SQLiteLockFile('somefile') >>> lock = SQLiteLockFile('somefile', threaded=False) """ LockBase.__init__(self, path, threaded, timeout) self.lock_file = unicode(self.lock_file) self.unique_name = unicode(self.unique_name) if SQLiteLockFile.testdb is None: import tempfile _fd, testdb = tempfile.mkstemp() os.close(_fd) os.unlink(testdb) del _fd, tempfile SQLiteLockFile.testdb = testdb import sqlite3 self.connection = sqlite3.connect(SQLiteLockFile.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, SQLiteLockFile.testdb) def acquire(self, timeout=None): timeout = timeout if timeout is not None else self.timeout 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("Timeout waiting to acquire" " lock for %s" % self.path) else: # Someone else has the lock and we are impatient.. raise AlreadyLocked("%s is already locked" % self.path) # Well, okay. We'll give it a bit longer. time.sleep(wait) def release(self): if not self.is_locked(): raise NotLocked("%s is not locked" % self.path) if not self.i_am_locking(): raise NotMyLock("%s is locked, but not by me (by %s)" % (self.unique_name, self._who_is_locking())) 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()