##// END OF EJS Templates
lock: fix race in lock-breaking code...
lock: fix race in lock-breaking code With low frequency, I see hg pulls fail with output like: abort: no such file or directory: .hg/store/lock I think what happens is, in lock.py, in: def _testlock(self, locker): if not self._lockshouldbebroken(locker): return locker # if locker dead, break lock. must do this with another lock # held, or can race and break valid lock. try: with lock(self.vfs, self.f + b'.break', timeout=0): self.vfs.unlink(self.f) except error.LockError: return locker if a lock is breakable on disk, and two hg processes concurrently get to the "if locker dead" comment, a possible interleaving is: process1 finishes executing the function and then process2 finishes executing the function. If that happens, process2 will either get ENOENT in self.vfs.unlink (resulting in the spurious failure above), or break a valid lock and potentially cause repository corruption. The fix is simple enough: make sure the lock is breakable _inside_ the critical section, because only then can we know that no other process can invalidate our knowledge on the lock on disk. I don't think there are tests for this. I've tested this manually with: diff --git a/mercurial/lock.py b/mercurial/lock.py --- a/mercurial/lock.py +++ b/mercurial/lock.py @@ -351,6 +351,8 @@ class lock(object): if not self._lockshouldbebroken(locker): return locker + import random + time.sleep(1. + random.random()) # if locker dead, break lock. must do this with another lock # held, or can race and break valid lock. try: @@ -358,6 +360,7 @@ class lock(object): self.vfs.unlink(self.f) except error.LockError: return locker + time.sleep(1) def testlock(self): """return id of locker if lock is valid, else None. and I see this change of behavior before/after this commit: $ $hg init repo $ cd repo $ ln -s $HOSTNAME/effffffc:987654321 .hg/wlock $ touch a $ $hg commit -Am_ & $hg commit -Am _; wait -abort: No such file or directory: '/tmp/repo/.hg/wlock' adding a +warning: ignoring unknown working parent 679a8959a8ca! +nothing changed Differential Revision: https://phab.mercurial-scm.org/D7199

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_compat.py
60 lines | 1.7 KiB | text/x-python | PythonLexer
##############################################################################
#
# Copyright (c) 2006 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.
#
##############################################################################
"""Basic components support
"""
from __future__ import absolute_import
import sys
import types
if sys.version_info[0] < 3:
def _normalize_name(name):
if isinstance(name, basestring):
return unicode(name)
raise TypeError("name must be a regular or unicode string")
CLASS_TYPES = (type, types.ClassType)
STRING_TYPES = (basestring,)
_BUILTINS = '__builtin__'
PYTHON3 = False
PYTHON2 = True
else:
def _normalize_name(name):
if isinstance(name, bytes):
name = str(name, 'ascii')
if isinstance(name, str):
return name
raise TypeError("name must be a string or ASCII-only bytes")
CLASS_TYPES = (type,)
STRING_TYPES = (str,)
_BUILTINS = 'builtins'
PYTHON3 = True
PYTHON2 = False
def _skip_under_py3k(test_method):
import unittest
return unittest.skipIf(sys.version_info[0] >= 3, "Only on Python 2")(test_method)
def _skip_under_py2(test_method):
import unittest
return unittest.skipIf(sys.version_info[0] < 3, "Only on Python 3")(test_method)