Mercurial > hg
view tests/test-convert-clonebranches.t @ 43709:039fbd14d4e2
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_ & $hg commit -Am _; wait
-abort: No such file or directory: '/tmp/repo/.hg/wlock'
adding a
+warning: ignoring unknown working parent 679a8959a8ca!
+nothing changed
Differential Revision: https://phab.mercurial-scm.org/D7199
author | Valentin Gatien-Baron <valentin.gatienbaron@gmail.com> |
---|---|
date | Mon, 18 Nov 2019 20:10:38 -0800 |
parents | 5abc47d4ca6b |
children | 42d2b31cee0b |
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$ cat <<EOF >> $HGRCPATH > [extensions] > convert = > [convert] > hg.tagsbranch = 0 > EOF $ hg init source $ cd source $ echo a > a $ hg ci -qAm adda Add a merge with one parent in the same branch $ echo a >> a $ hg ci -qAm changea $ hg up -qC 0 $ hg branch branch0 marked working directory as branch branch0 (branches are permanent and global, did you want a bookmark?) $ echo b > b $ hg ci -qAm addb $ hg up -qC $ hg merge default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg ci -qm mergeab $ hg tag -ql mergeab $ cd .. Miss perl... sometimes $ cat > filter.py <<EOF > from __future__ import absolute_import > import re > import sys > > r = re.compile(r'^(?:\d+|pulling from)') > sys.stdout.writelines([l for l in sys.stdin if r.search(l)]) > EOF convert $ hg convert -v --config convert.hg.clonebranches=1 source dest | > "$PYTHON" filter.py 3 adda 2 changea 1 addb pulling from default into branch0 1 changesets found 0 mergeab pulling from default into branch0 1 changesets found Add a merge with both parents and child in different branches $ cd source $ hg branch branch1 marked working directory as branch branch1 $ echo a > file1 $ hg ci -qAm c1 $ hg up -qC mergeab $ hg branch branch2 marked working directory as branch branch2 $ echo a > file2 $ hg ci -qAm c2 $ hg merge branch1 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg branch branch3 marked working directory as branch branch3 $ hg ci -qAm c3 $ cd .. incremental conversion $ hg convert -v --config convert.hg.clonebranches=1 source dest | > "$PYTHON" filter.py 2 c1 pulling from branch0 into branch1 4 changesets found 1 c2 pulling from branch0 into branch2 4 changesets found 0 c3 pulling from branch1 into branch3 5 changesets found pulling from branch2 into branch3 1 changesets found