##// 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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verify.py
122 lines | 4.6 KiB | text/x-python | PythonLexer
##############################################################################
#
# 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.
#
##############################################################################
"""Verify interface implementations
"""
from __future__ import absolute_import
from .exceptions import BrokenImplementation, DoesNotImplement
from .exceptions import BrokenMethodImplementation
from types import FunctionType, MethodType
from .interface import fromMethod, fromFunction, Method
import sys
# This will be monkey-patched when running under Zope 2, so leave this
# here:
MethodTypes = (MethodType, )
def _verify(iface, candidate, tentative=0, vtype=None):
"""Verify that 'candidate' might correctly implements 'iface'.
This involves:
o Making sure the candidate defines all the necessary methods
o Making sure the methods have the correct signature
o Making sure the candidate asserts that it implements the interface
Note that this isn't the same as verifying that the class does
implement the interface.
If optional tentative is true, suppress the "is implemented by" test.
"""
if vtype == 'c':
tester = iface.implementedBy
else:
tester = iface.providedBy
if not tentative and not tester(candidate):
raise DoesNotImplement(iface)
# Here the `desc` is either an `Attribute` or `Method` instance
for name, desc in iface.namesAndDescriptions(1):
try:
attr = getattr(candidate, name)
except AttributeError:
if (not isinstance(desc, Method)) and vtype == 'c':
# We can't verify non-methods on classes, since the
# class may provide attrs in it's __init__.
continue
raise BrokenImplementation(iface, name)
if not isinstance(desc, Method):
# If it's not a method, there's nothing else we can test
continue
if isinstance(attr, FunctionType):
if sys.version_info[0] >= 3 and isinstance(candidate, type):
# This is an "unbound method" in Python 3.
meth = fromFunction(attr, iface, name=name,
imlevel=1)
else:
# Nope, just a normal function
meth = fromFunction(attr, iface, name=name)
elif (isinstance(attr, MethodTypes)
and type(attr.__func__) is FunctionType):
meth = fromMethod(attr, iface, name)
elif isinstance(attr, property) and vtype == 'c':
# We without an instance we cannot be sure it's not a
# callable.
continue
else:
if not callable(attr):
raise BrokenMethodImplementation(name, "Not a method")
# sigh, it's callable, but we don't know how to introspect it, so
# we have to give it a pass.
continue
# Make sure that the required and implemented method signatures are
# the same.
desc = desc.getSignatureInfo()
meth = meth.getSignatureInfo()
mess = _incompat(desc, meth)
if mess:
raise BrokenMethodImplementation(name, mess)
return True
def verifyClass(iface, candidate, tentative=0):
return _verify(iface, candidate, tentative, vtype='c')
def verifyObject(iface, candidate, tentative=0):
return _verify(iface, candidate, tentative, vtype='o')
def _incompat(required, implemented):
#if (required['positional'] !=
# implemented['positional'][:len(required['positional'])]
# and implemented['kwargs'] is None):
# return 'imlementation has different argument names'
if len(implemented['required']) > len(required['required']):
return 'implementation requires too many arguments'
if ((len(implemented['positional']) < len(required['positional']))
and not implemented['varargs']):
return "implementation doesn't allow enough arguments"
if required['kwargs'] and not implemented['kwargs']:
return "implementation doesn't support keyword arguments"
if required['varargs'] and not implemented['varargs']:
return "implementation doesn't support variable arguments"