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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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Matt Harbison
help: create packages for the help text...
 r44031 Mercurial's internal web server, hgweb, can serve either a single
repository, or a tree of repositories. In the second case, repository
paths and global options can be defined using a dedicated
configuration file common to :hg:`serve`, ``hgweb.wsgi``,
``hgweb.cgi`` and ``hgweb.fcgi``.
This file uses the same syntax as other Mercurial configuration files
but recognizes only the following sections:
- web
- paths
- collections
The ``web`` options are thoroughly described in :hg:`help config`.
The ``paths`` section maps URL paths to paths of repositories in the
filesystem. hgweb will not expose the filesystem directly - only
Mercurial repositories can be published and only according to the
configuration.
The left hand side is the path in the URL. Note that hgweb reserves
subpaths like ``rev`` or ``file``, try using different names for
nested repositories to avoid confusing effects.
The right hand side is the path in the filesystem. If the specified
path ends with ``*`` or ``**`` the filesystem will be searched
recursively for repositories below that point.
With ``*`` it will not recurse into the repositories it finds (except for
``.hg/patches``).
With ``**`` it will also search inside repository working directories
and possibly find subrepositories.
In this example::
[paths]
/projects/a = /srv/tmprepos/a
/projects/b = c:/repos/b
/ = /srv/repos/*
/user/bob = /home/bob/repos/**
- The first two entries make two repositories in different directories
appear under the same directory in the web interface
- The third entry will publish every Mercurial repository found in
``/srv/repos/``, for instance the repository ``/srv/repos/quux/``
will appear as ``http://server/quux/``
- The fourth entry will publish both ``http://server/user/bob/quux/``
and ``http://server/user/bob/quux/testsubrepo/``
The ``collections`` section is deprecated and has been superseded by
``paths``.
URLs and Common Arguments
=========================
URLs under each repository have the form ``/{command}[/{arguments}]``
where ``{command}`` represents the name of a command or handler and
``{arguments}`` represents any number of additional URL parameters
to that command.
The web server has a default style associated with it. Styles map to
a collection of named templates. Each template is used to render a
specific piece of data, such as a changeset or diff.
The style for the current request can be overwritten two ways. First,
if ``{command}`` contains a hyphen (``-``), the text before the hyphen
defines the style. For example, ``/atom-log`` will render the ``log``
command handler with the ``atom`` style. The second way to set the
style is with the ``style`` query string argument. For example,
``/log?style=atom``. The hyphenated URL parameter is preferred.
Not all templates are available for all styles. Attempting to use
a style that doesn't have all templates defined may result in an error
rendering the page.
Many commands take a ``{revision}`` URL parameter. This defines the
changeset to operate on. This is commonly specified as the short,
12 digit hexadecimal abbreviation for the full 40 character unique
revision identifier. However, any value described by
:hg:`help revisions` typically works.
Commands and URLs
=================
The following web commands and their URLs are available:
.. webcommandsmarker