##############################################################################
#
# Copyright (c) 2001, 2002 Zope Corporation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.0 (ZPL). A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE
#
##############################################################################
"""Mounted database support
$Id$"""
import string
import time
import sys
import thread
import logging
import persistent
import Acquisition
from Acquisition import aq_base
from POSException import MountedStorageError
logger = logging.getLogger('ZODB.Mount')
# dbs is a holder for all DB objects, needed to overcome
# threading issues. It maps connection params to a DB object
# and a mapping of mount points.
dbs = {}
# dblock is locked every time dbs is accessed.
dblock=thread.allocate_lock()
def parentClassFactory(jar, module, name):
# Use the class factory from the parent database.
parent_conn = getattr(jar, '_mount_parent_jar', None)
parent_db = getattr(parent_conn, '_db', None)
if parent_db is None:
_globals = {}
_silly = ('__doc__',)
return getattr(__import__(
module, _globals, _globals, _silly), name)
else:
return parent_db.classFactory(parent_conn, module, name)
class MountPoint(persistent.Persistent, Acquisition.Implicit):
'''The base class for a Zope object which, when traversed,
accesses a different database.
'''
# Default values for non-persistent variables.
_v_db = None
_v_data = None
_v_connect_error = None
def __init__(self, path, params=None, classDefsFromRoot=1):
'''
@arg path The path within the mounted database from which
to derive the root.
@arg params The parameters used to connect to the database.
No particular format required.
If there is more than one mount point referring to a
database, MountPoint will detect the matching params
and use the existing database. Include the class name of
the storage. For example,
ZEO params might be "ZODB.ZEOClient localhost 1081".
@arg classDefsFromRoot If true (the default), MountPoint will
try to get ZClass definitions from the root database rather
than the mounted database.
'''
# The only reason we need a __mountpoint_id is to
# be sure we don't close a database prematurely when
# it is mounted more than once and one of the points
# is unmounted.
self.__mountpoint_id = '%s_%f' % (id(self), time.time())
if params is None:
# We still need something to use as a hash in
# the "dbs" dictionary.
params = self.__mountpoint_id
self._params = repr(params)
self._path = path
self._classDefsFromRoot = classDefsFromRoot
def _createDB(self):
'''Gets the database object, usually by creating a Storage object
and returning ZODB.DB(storage).
'''
raise NotImplementedError
def _getDB(self):
'''Creates or opens a DB object.
'''
newMount = 0
dblock.acquire()
try:
params = self._params
dbInfo = dbs.get(params, None)
if dbInfo is None:
logger.info('Opening database for mounting: %s', params)
db = self._createDB()
newMount = 1
dbs[params] = (db, {self.__mountpoint_id:1})
if getattr(self, '_classDefsFromRoot', 1):
db.classFactory = parentClassFactory
else:
db, mounts = dbInfo
# Be sure this object is in the list of mount points.
if not mounts.has_key(self.__mountpoint_id):
newMount = 1
mounts[self.__mountpoint_id] = 1
self._v_db = db
finally:
dblock.release()
return db, newMount
def _getMountpointId(self):
return self.__mountpoint_id
def _getMountParams(self):
return self._params
def __repr__(self):
return "%s(%s, %s)" % (self.__class__.__name__, repr(self._path),
self._params)
def _openMountableConnection(self, parent):
# Opens a new connection to the database.
db = self._v_db
if db is None:
self._v_close_db = 0
db, newMount = self._getDB()
else:
newMount = 0
jar = getattr(self, '_p_jar', None)
if jar is None:
# Get _p_jar from parent.
self._p_jar = jar = parent._p_jar
conn = db.open(version=jar.getVersion())
# Add an attribute to the connection which
# makes it possible for us to find the primary
# database connection. See ClassFactoryForMount().
conn._mount_parent_jar = jar
mcc = MountedConnectionCloser(self, conn)
jar.onCloseCallback(mcc)
return conn, newMount, mcc
def _getObjectFromConnection(self, conn):
obj = self._getMountRoot(conn.root())
data = aq_base(obj)
# Store the data object in a tuple to hide from acquisition.
self._v_data = (data,)
return data
def _getOrOpenObject(self, parent):
t = self._v_data
if t is None:
self._v_connect_error = None
conn = None
newMount = 0
mcc = None
try:
conn, newMount, mcc = self._openMountableConnection(parent)
data = self._getObjectFromConnection(conn)
except:
# Possibly broken database.
if mcc is not None:
# Note that the next line may be a little rash--
# if, for example, a working database throws an
# exception rather than wait for a new connection,
# this will likely cause the database to be closed
# prematurely. Perhaps DB.py needs a
# countActiveConnections() method.
mcc.setCloseDb()
self._logConnectException()
raise
if newMount:
try: id = data.getId()
except: id = '???' # data has no getId() method. Bad.
p = string.join(parent.getPhysicalPath() + (id,), '/')
logger.info('Mounted database %s at %s',
self._getMountParams(), p)
else:
data = t[0]
return data.__of__(parent)
def __of__(self, parent):
# Accesses the database, returning an acquisition
# wrapper around the connected object rather than around self.
try:
return self._getOrOpenObject(parent)
except:
return Acquisition.ImplicitAcquisitionWrapper(
self, parent)
def _test(self, parent):
'''Tests the database connection.
'''
self._getOrOpenObject(parent)
return 1
def _getMountRoot(self, root):
'''Gets the object to be mounted.
Can be overridden to provide different behavior.
'''
try:
app = root['Application']
except:
raise MountedStorageError, (
"No 'Application' object exists in the mountable database.")
try:
return app.unrestrictedTraverse(self._path)
except:
raise MountedStorageError, (
"The path '%s' was not found in the mountable database."
% self._path)
def _logConnectException(self):
'''Records info about the exception that just occurred.
'''
try:
from cStringIO import StringIO
except:
from StringIO import StringIO
import traceback
logger.warning('Failed to mount database. %s (%s)', exc[:2],
exc_info=True)
f=StringIO()
traceback.print_tb(exc[2], 100, f)
self._v_connect_error = (exc[0], exc[1], f.getvalue())
exc = None
class MountedConnectionCloser:
'''Closes the connection used by the mounted database
while performing other cleanup.
'''
close_db = 0
def __init__(self, mountpoint, conn):
# conn is the child connection.
self.mp = mountpoint
self.conn = conn
def setCloseDb(self):
self.close_db = 1
def __call__(self):
# The onCloseCallback handler.
# Closes a single connection to the database
# and possibly the database itself.
conn = self.conn
close_db = 0
if conn is not None:
mp = self.mp
# Remove potential circular references.
self.conn = None
self.mp = None
# Detect whether we should close the database.
close_db = self.close_db
t = mp.__dict__.get('_v_data', None)
if t is not None:
del mp.__dict__['_v_data']
data = t[0]
if not close_db and data.__dict__.get(
'_v__object_deleted__', 0):
# This mount point has been deleted.
del data.__dict__['_v__object_deleted__']
close_db = 1
# Close the child connection.
try:
del conn._mount_parent_jar
except:
pass
conn.close()
if close_db:
# Stop using this database. Close it if no other
# MountPoint is using it.
dblock.acquire()
try:
params = mp._getMountParams()
mp._v_db = None
if dbs.has_key(params):
dbInfo = dbs[params]
db, mounts = dbInfo
try: del mounts[mp._getMountpointId()]
except: pass
if len(mounts) < 1:
# No more mount points are using this database.
del dbs[params]
db.close()
logger.info('Closed database: %s', params)
finally:
dblock.release()