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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
Matt Harbison - - Load All Authors

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urls.txt
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Valid URLs are of the form::
local/filesystem/path[#revision]
file://local/filesystem/path[#revision]
http://[user[:pass]@]host[:port]/[path][#revision]
https://[user[:pass]@]host[:port]/[path][#revision]
ssh://[user@]host[:port]/[path][#revision]
Paths in the local filesystem can either point to Mercurial
repositories or to bundle files (as created by :hg:`bundle` or
:hg:`incoming --bundle`). See also :hg:`help paths`.
An optional identifier after # indicates a particular branch, tag, or
changeset to use from the remote repository. See also :hg:`help
revisions`.
Some features, such as pushing to http:// and https:// URLs are only
possible if the feature is explicitly enabled on the remote Mercurial
server.
Note that the security of HTTPS URLs depends on proper configuration of
web.cacerts.
Some notes about using SSH with Mercurial:
- SSH requires an accessible shell account on the destination machine
and a copy of hg in the remote path or specified with remotecmd.
- path is relative to the remote user's home directory by default. Use
an extra slash at the start of a path to specify an absolute path::
ssh://example.com//tmp/repository
- Mercurial doesn't use its own compression via SSH; the right thing
to do is to configure it in your ~/.ssh/config, e.g.::
Host *.mylocalnetwork.example.com
Compression no
Host *
Compression yes
Alternatively specify "ssh -C" as your ssh command in your
configuration file or with the --ssh command line option.
These URLs can all be stored in your configuration file with path
aliases under the [paths] section like so::
[paths]
alias1 = URL1
alias2 = URL2
...
You can then use the alias for any command that uses a URL (for
example :hg:`pull alias1` will be treated as :hg:`pull URL1`).
Two path aliases are special because they are used as defaults when
you do not provide the URL to a command:
default:
When you create a repository with hg clone, the clone command saves
the location of the source repository as the new repository's
'default' path. This is then used when you omit path from push- and
pull-like commands (including incoming and outgoing).
default-push:
The push command will look for a path named 'default-push', and
prefer it over 'default' if both are defined.