Viewing file:  sqlitelockfile.py (5.38 KB) -rw-r--r--
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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()
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