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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
Pulkit Goyal - - Load All Authors

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README.rst
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Pulkit Goyal
thirdparty: vendor cbor2 python library...
 r37144 .. image:: https://travis-ci.org/agronholm/cbor2.svg?branch=master
:target: https://travis-ci.org/agronholm/cbor2
:alt: Build Status
.. image:: https://coveralls.io/repos/github/agronholm/cbor2/badge.svg?branch=master
:target: https://coveralls.io/github/agronholm/cbor2?branch=master
:alt: Code Coverage
This library provides encoding and decoding for the Concise Binary Object Representation (CBOR)
(`RFC 7049`_) serialization format.
There exists another Python CBOR implementation (cbor) which is faster on CPython due to its C
extensions. On PyPy, cbor2 and cbor are almost identical in performance. The other implementation
also lacks documentation and a comprehensive test suite, does not support most standard extension
tags and is known to crash (segfault) when passed a cyclic structure (say, a list containing
itself).
.. _RFC 7049: https://tools.ietf.org/html/rfc7049
Project links
-------------
* `Documentation <http://cbor2.readthedocs.org/>`_
* `Source code <https://github.com/agronholm/cbor2>`_
* `Issue tracker <https://github.com/agronholm/cbor2/issues>`_