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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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flags.txt
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Most Mercurial commands accept various flags.
Flag names
==========
Flags for each command are listed in :hg:`help` for that command.
Additionally, some flags, such as --repository, are global and can be used with
any command - those are seen in :hg:`help -v`, and can be specified before or
after the command.
Every flag has at least a long name, such as --repository. Some flags may also
have a short one-letter name, such as the equivalent -R. Using the short or long
name is equivalent and has the same effect.
Flags that have a short name can also be bundled together - for instance, to
specify both --edit (short -e) and --interactive (short -i), one could use::
hg commit -ei
If any of the bundled flags takes a value (i.e. is not a boolean), it must be
last, followed by the value::
hg commit -im 'Message'
Flag types
==========
Mercurial command-line flags can be strings, numbers, booleans, or lists of
strings.
Specifying flag values
======================
The following syntaxes are allowed, assuming a flag 'flagname' with short name
'f'::
--flagname=foo
--flagname foo
-f foo
-ffoo
This syntax applies to all non-boolean flags (strings, numbers or lists).
Specifying boolean flags
========================
Boolean flags do not take a value parameter. To specify a boolean, use the flag
name to set it to true, or the same name prefixed with 'no-' to set it to
false::
hg commit --interactive
hg commit --no-interactive
Specifying list flags
=====================
List flags take multiple values. To specify them, pass the flag multiple times::
hg files --include mercurial --include tests
Setting flag defaults
=====================
In order to set a default value for a flag in an hgrc file, it is recommended to
use aliases::
[alias]
commit = commit --interactive
For more information on hgrc files, see :hg:`help config`.
Overriding flags on the command line
====================================
If the same non-list flag is specified multiple times on the command line, the
latest specification is used::
hg commit -m "Ignored value" -m "Used value"
This includes the use of aliases - e.g., if one has::
[alias]
committemp = commit -m "Ignored value"
then the following command will override that -m::
hg committemp -m "Used value"
Overriding flag defaults
========================
Every flag has a default value, and you may also set your own defaults in hgrc
as described above.
Except for list flags, defaults can be overridden on the command line simply by
specifying the flag in that location.
Hidden flags
============
Some flags are not shown in a command's help by default - specifically, those
that are deemed to be experimental, deprecated or advanced. To show all flags,
add the --verbose flag for the help command::
hg help --verbose commit