Commit e11edc70 authored by Kirill Smelkov's avatar Kirill Smelkov

wcfs: client: Add wczsync package to maintain WCFS connection in sync to ZODB connection

For ZBigFile + WCFS client integration we'll need to open WCFS
connections that observer database at the same state as current ZODB
connection. Later that WCFS connection needs to adjust its on-WCFS view
in accordance to how ZODB connection adjusts its one.

Wczsync provides a function to do so: pywconnOf(zconn) will open WCFS
connection and maintain it in sync with ZODB connection zconn.

Some preliminary history:

8bf8f23b    X bigfile/_file_zodb: Fix logic around ZSync usage
571cb737    fixup! X bigfile/_file_zodb: Fix logic around ZSync usage
a9a82d5a    X bigfile/_file_zodb: Fix ZSync to close not only wconn, but also wconn.wc through which wconn was created
cf92937f    X wcfs: Move wconn<->zconn sync functionality into wcfs.client._wczsync
7203d7ab    X wcfs: Fix ZSync to close wconn on zdb.close, even if zconn stays alive
parent 1f866c00
...@@ -336,6 +336,13 @@ setup( ...@@ -336,6 +336,13 @@ setup(
depends = libwcfs_h, depends = libwcfs_h,
dsos = ['wendelin.wcfs.client.libwcfs']), dsos = ['wendelin.wcfs.client.libwcfs']),
PyGoExt('wendelin.wcfs.client._wczsync',
['wcfs/client/_wczsync.pyx'],
depends = [
'wcfs/client/_wcfs.pxd',
] + libwcfs_h,
dsos = ['wendelin.wcfs.client.libwcfs']),
PyGoExt('wendelin.wcfs.internal.wcfs_test', PyGoExt('wendelin.wcfs.internal.wcfs_test',
['wcfs/internal/wcfs_test.pyx']), ['wcfs/internal/wcfs_test.pyx']),
......
/_wcfs.cpp /_wcfs.cpp
/_wczsync.cpp
# -*- coding: utf-8 -*-
# Copyright (C) 2018-2021 Nexedi SA and Contributors.
# Kirill Smelkov <kirr@nexedi.com>
#
# This program is free software: you can Use, Study, Modify and Redistribute
# it under the terms of the GNU General Public License version 3, or (at your
# option) any later version, as published by the Free Software Foundation.
#
# You can also Link and Combine this program with other software covered by
# the terms of any of the Free Software licenses or any of the Open Source
# Initiative approved licenses and Convey the resulting work. Corresponding
# source of such a combination shall include the source code for all other
# software used.
#
# This program is distributed WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#
# See COPYING file for full licensing terms.
# See https://www.nexedi.com/licensing for rationale and options.
# cython: language_level=2
# distutils: language=c++
# Package _wczsync provides way to keep WCFS and ZODB connections in sync.
#
# Use pywconnOf(zconn) to establish and return WCFS connection that matches and
# is kept in sync with ZODB connection zconn.
from wendelin.wcfs.client cimport _wcfs as wcfs
cdef wcfs.PyConn pywconnOf(zconn)
# -*- coding: utf-8 -*-
# Copyright (C) 2018-2021 Nexedi SA and Contributors.
# Kirill Smelkov <kirr@nexedi.com>
#
# This program is free software: you can Use, Study, Modify and Redistribute
# it under the terms of the GNU General Public License version 3, or (at your
# option) any later version, as published by the Free Software Foundation.
#
# You can also Link and Combine this program with other software covered by
# the terms of any of the Free Software licenses or any of the Open Source
# Initiative approved licenses and Convey the resulting work. Corresponding
# source of such a combination shall include the source code for all other
# software used.
#
# This program is distributed WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#
# See COPYING file for full licensing terms.
# See https://www.nexedi.com/licensing for rationale and options.
# cython: language_level=2
# cython: auto_pickle=False
# distutils: language=c++
# Package _wczsync provides way to keep WCFS and ZODB connections in sync.
# See _wczsync.pxd for package overview.
from wendelin import wcfs as pywcfs
from wendelin.lib import zodb as pyzodb
from ZODB.Connection import Connection as ZConnection
from ZODB.utils import u64
from wendelin.lib.zodb import zconn_at
import weakref
# pywconnOf establishes and returns (py) wcfs.Conn associated with zconn.
#
# returned wcfs.Conn will be maintained to keep in sync with zconn, and will be
# closed when zconn is destroyed.
#
# It is invalid to make multiple simultaneous calls to pywconnOf with the same zconn.
# (in ZODB/py objects for zconn must be used from under 1 thread only).
cdef wcfs.PyConn pywconnOf(zconn):
assert isinstance(zconn, ZConnection)
assert zconn.opened
wconn = getattr(zconn, '_wcfs_wconn', None)
if wconn is not None:
return wconn
# zconn is not yet associated with wconn
zstor = zconn.db().storage
zurl = pyzodb.zstor_2zurl(zstor)
wc = pywcfs.join(zurl)
wconn = wc.connect(zconn_at(zconn))
zconn._wcfs_wconn = wconn
# keep wconn view of the database in sync with zconn
# wconn and wc (= wconn.wc) will be closed when zconn is garbage-collected or shutdown via DB.close
_ZSync(zconn, wconn)
return wconn
# _ZSync keeps wconn in sync with zconn.
#
# wconn will be closed once zconn is garbage-collected (not closed, which
# returns it back into DB pool), or once zconn.db is closed.
#
# _ZSync cares itself to stay alive as long as zconn stays alive.
_zsyncReg = {} # id(zsync) -> zsync (protected by GIL)
class _ZSync:
# .zconn_ref weakref[zodb.Connection]
# .wconn (py) wcfs.Connection
def __init__(zsync, zconn, wconn):
#print('ZSync: setup %r <-> %r' % (wconn, zconn))
assert zconn.opened
zsync.wconn = wconn
# notify us on zconn GC
zsync.zconn_ref = weakref.ref(zconn, zsync.on_zconn_dealloc)
# notify us on zconn.db.close
zconn.onShutdownCallback(zsync)
# notify us when zconn changes its view of the database
# NOTE zconn.onOpenCallback is not enough: zconn.at can change even
# without zconn.close/zconn.open, e.g.:
# zconn = DB.open(transaction_manager=tm)
# tm.commit() # zconn.at updated (zconn.afterCompletion -> zconn.newTransaction)
# tm.commit() # zconn.at updated again
zconn.onResyncCallback(zsync)
# keep zsync in _zsyncReg for zsync to stay alive independently of the caller.
#
# NOTE we cannot use regular mutex to protect _zsyncReg updates because
# the other _zsyncReg mutator (on_zconn_dealloc) is invoked by
# automatic GC that can be triggered any time.
#
# on CPython dict updates are "atomic" - they happen without releasing GIL.
if 1: # = `with gil:` (GIL already held in python code)
_zsyncReg[id(zsync)] = zsync
# _release1 closes .wconn and releases zsync once.
def _release1(zsync):
# unregister zsync from being kept alive
if 1: # = `with gil:` (see note in __init__)
_ = _zsyncReg.pop(id(zsync), None)
if _ is None:
return # another call already done/is simultaneously doing release1
#print('ZSync: sched break %r <-> .' % (zsync.wconn,))
# schedule wconn.close() + wconn.wc.close()
_zsync_wclose_wg.add(1)
go(_wclose1, zsync.wconn)
# XXX how to safely schedule work to _zsync_releaser without blocking weakref callback?
"""
# (we cannot do this from under weakref callback - see _zsync_releaser for details)
_zsync_releaseq.append(...)
_zsync_releaseq.send(zsync.wconn)
"""
# .zconn dealloc -> wconn.close; release zsync.
def on_zconn_dealloc(zsync, _):
zsync._release1()
# DB.close -> wconn.close; release zsync.
def on_connection_shutdown(zsync):
zsync._release1()
# DB resyncs .zconn onto new database view.
# -> resync .wconn to updated database view of ZODB connection.
def on_connection_resync(zsync):
zconn = zsync.zconn_ref()
zsync.wconn.resync(zconn_at(zconn))
from golang import go
from golang import sync
# XXX disabled for now (not sure how to safely schedule work from under weakref callback)
# -> doing straight `go _wclose1` every time.
"""
from golang import go, chan
import logging as log
# _zsync_releaser is dedicated thread that closes wconn/wc after ZSync detects
# that zconn - to which wconn was associated - is no longer alive.
#
# Requests to _zsync_releaser come from ZSync.on_zconn_dealloc - which is
# called from under weakref callback when zconn is garbage collected. Since it
# is not safe to take python-level locks from under __del__ or weakref callback
# (that can cause deadlocks), the releasing work is scheduled to be done in
# separate _zsync_releaser thread.
#
# The need to take locks: even though wconn.close() can work without taking
# py-level locks, wc.close needs to take wcfs._wcmu
_zsync_releaseq = [] # of wconn
_zsync_wakeup = chan(1)
def _zsync_releaser():
while 1:
wconn, ok = _zsync_releaseq.recv_()
if not ok:
break # time to stop XXX needed?
# let's close wconn and its .wc
try:
1/0
_wclose1(wconn)
except:
log.exception("zsync: releaser: wclose %r", wconn)
# XXX nrelease += 1
go(_zsync_releaser)
"""
_zsync_wclose_wg = sync.WaitGroup()
def _wclose1(wconn):
#print('ZSync: break %r <-> .' % (wconn,))
wc = wconn.wc
wconn.close()
wc.close()
_zsync_wclose_wg.done()
# at shutdown make sure there is no in-flight _wclose1
import atexit; atexit.register(_zsync_wclose_wg.wait)
# -*- coding: utf-8 -*-
# Wendelin.bigfile | Tests for WCFS part of BigFile ZODB backend
# Copyright (C) 2020-2021 Nexedi SA and Contributors.
# Kirill Smelkov <kirr@nexedi.com>
#
# This program is free software: you can Use, Study, Modify and Redistribute
# it under the terms of the GNU General Public License version 3, or (at your
# option) any later version, as published by the Free Software Foundation.
#
# You can also Link and Combine this program with other software covered by
# the terms of any of the Free Software licenses or any of the Open Source
# Initiative approved licenses and Convey the resulting work. Corresponding
# source of such a combination shall include the source code for all other
# software used.
#
# This program is distributed WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#
# See COPYING file for full licensing terms.
# See https://www.nexedi.com/licensing for rationale and options.
from wendelin.wcfs.client._wczsync import _ZSync, _zsync_wclose_wg
from wendelin import wcfs
from wendelin.lib.zodb import zstor_2zurl, zconn_at
from wendelin.lib.testing import getTestDB
from ZODB import DB
from ZODB.utils import p64
import transaction
from golang import defer, func, error
import weakref, gc
from pytest import raises
testdb = None
def setup_module():
global testdb
testdb = getTestDB()
testdb.setup()
def teardown_module():
testdb.teardown()
# _zsync_setup setups up DB, zconn and wconn _ZSync'ed to zconn.
@func
def _zsync_setup(zstor): # -> (db, zconn, wconn)
zurl = zstor_2zurl(zstor)
# create new DB that we'll precisely control
db = DB(zstor)
zconn = db.open()
at0 = zconn_at(zconn)
# create wconn
wc = wcfs.join(zurl)
wconn = wc.connect(at0)
assert wconn.at() == at0
# setup ZSync for wconn <-> zconn; don't keep zsync explicitly referenced
# NOTE ZSync takes ownership of wconn.wc (= wc), so we don't wc.close
_ZSync(zconn, wconn)
assert wconn.at() == at0
return db, zconn, wconn
# verify that ZSync closes wconn when db is closed.
@func
def test_zsync_db_close():
zstor = testdb.getZODBStorage()
defer(zstor.close)
db, zconn, wconn = _zsync_setup(zstor)
defer(wconn.close)
# close db -> ZSync should close wconn and wc even though zconn stays referenced
wc_njoin0 = wconn.wc._njoin
db.close()
_zsync_wclose_wg.wait()
# NOTE db and zconn are still alive - not GC'ed
with raises(error, match=": connection closed"):
wconn.open(p64(0))
assert wconn.wc._njoin == (wc_njoin0 - 1)
# verify that ZSync closes wconn when zconn is garbage-collected.
@func
def test_zsync_zconn_gc():
zstor = testdb.getZODBStorage()
defer(zstor.close)
db, zconn, wconn = _zsync_setup(zstor)
defer(wconn.close)
# del zconn -> zconn should disappear and ZSync should close wconn and wc
zconn_weak = weakref.ref(zconn)
assert zconn_weak() is not None
wc_njoin0 = wconn.wc._njoin
del zconn
# NOTE db stays alive and not closed
gc.collect()
assert zconn_weak() is None
_zsync_wclose_wg.wait()
with raises(error, match=": connection closed"):
wconn.open(p64(0))
assert wconn.wc._njoin == (wc_njoin0 - 1)
# verify that ZSync keeps wconn in sync wrt zconn.
@func
def test_zsync_resync():
zstor = testdb.getZODBStorage()
defer(zstor.close)
db, zconn, wconn = _zsync_setup(zstor)
defer(db.close)
# commit something - ZSync should resync wconn to updated db state
at0 = zconn_at(zconn)
assert wconn.at() == at0
root = zconn.root()
root['tzync'] = 1
transaction.commit()
del root
at1 = zconn_at(zconn)
assert at1 != at0
assert wconn.at() == at1
# commit something via different zconn2 - wconn stays in sync with original zconn @at1
tm2 = transaction.TransactionManager()
zconn2 = db.open(transaction_manager=tm2)
assert zconn_at(zconn2) == at1
root2 = zconn2.root()
root2['tzsync'] = 2
tm2.commit()
at2 = zconn_at(zconn2)
assert at2 != at1
assert zconn_at(zconn) == at1
assert wconn.at() == at1
# close zconn - it should stay in db.pool with wconn alive and still @at1
zconn_weak = weakref.ref(zconn)
assert zconn_weak() is zconn
zconn.close()
del zconn
gc.collect()
assert zconn_weak() is not None
assert wconn.at() == at1
# reopen db - it should return zconn and resynced to @at2; ZSync should keep wconn in sync
zconn = db.open()
assert zconn_weak() is zconn
assert zconn_at(zconn) == at2
assert wconn.at() == at2
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