/usr/share/pyshared/ZEO/TransactionBuffer.py is in python-zodb 1:3.9.7-2.
This file is owned by root:root, with mode 0o644.
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#
# Copyright (c) 2001, 2002 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (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
#
##############################################################################
"""A TransactionBuffer store transaction updates until commit or abort.
A transaction may generate enough data that it is not practical to
always hold pending updates in memory. Instead, a TransactionBuffer
is used to store the data until a commit or abort.
"""
# A faster implementation might store trans data in memory until it
# reaches a certain size.
from threading import Lock
import os
import cPickle
import tempfile
import ZODB.blob
class TransactionBuffer:
# Valid call sequences:
#
# ((store | invalidate)* begin_iterate next* clear)* close
#
# get_size can be called any time
# The TransactionBuffer is used by client storage to hold update
# data until the tpc_finish(). It is normally used by a single
# thread, because only one thread can be in the two-phase commit
# at one time.
# It is possible, however, for one thread to close the storage
# while another thread is in the two-phase commit. We must use
# a lock to guard against this race, because unpredictable things
# can happen in Python if one thread closes a file that another
# thread is reading. In a debug build, an assert() can fail.
# Caution: If an operation is performed on a closed TransactionBuffer,
# it has no effect and does not raise an exception. The only time
# this should occur is when a ClientStorage is closed in one
# thread while another thread is in its tpc_finish(). It's not
# clear what should happen in this case. If the tpc_finish()
# completes without error, the Connection using it could have
# inconsistent data. This should have minimal effect, though,
# because the Connection is connected to a closed storage.
def __init__(self):
self.file = tempfile.TemporaryFile(suffix=".tbuf")
self.lock = Lock()
self.closed = 0
self.count = 0
self.size = 0
self.blobs = []
# It's safe to use a fast pickler because the only objects
# stored are builtin types -- strings or None.
self.pickler = cPickle.Pickler(self.file, 1)
self.pickler.fast = 1
def close(self):
self.clear()
self.lock.acquire()
try:
self.closed = 1
try:
self.file.close()
except OSError:
pass
finally:
self.lock.release()
def store(self, oid, data):
"""Store oid, version, data for later retrieval"""
self.lock.acquire()
try:
if self.closed:
return
self.pickler.dump((oid, data))
self.count += 1
# Estimate per-record cache size
self.size = self.size + (data and len(data) or 0) + 31
finally:
self.lock.release()
def storeBlob(self, oid, blobfilename):
self.blobs.append((oid, blobfilename))
def invalidate(self, oid):
self.lock.acquire()
try:
if self.closed:
return
self.pickler.dump((oid, None))
self.count += 1
finally:
self.lock.release()
def clear(self):
"""Mark the buffer as empty"""
self.lock.acquire()
try:
if self.closed:
return
self.file.seek(0)
self.count = 0
self.size = 0
while self.blobs:
oid, blobfilename = self.blobs.pop()
if os.path.exists(blobfilename):
ZODB.blob.remove_committed(blobfilename)
finally:
self.lock.release()
def __iter__(self):
self.lock.acquire()
try:
if self.closed:
return
self.file.flush()
self.file.seek(0)
return TBIterator(self.file, self.count)
finally:
self.lock.release()
class TBIterator(object):
def __init__(self, f, count):
self.file = f
self.count = count
self.unpickler = cPickle.Unpickler(f)
def __iter__(self):
return self
def next(self):
"""Return next tuple of data or None if EOF"""
if self.count == 0:
self.file.seek(0)
self.size = 0
raise StopIteration
oid_ver_data = self.unpickler.load()
self.count -= 1
return oid_ver_data
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