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view mercurial/lock.py @ 48687:f8f2ecdde4b5
branchmap: skip obsolete revisions while computing heads
It's time to make this part of core Mercurial obsolescence-aware.
Not considering obsolete revisions when computing heads is clearly what
Mercurial should do. But there are a couple of small issues:
- Let's say tip of the repo is obsolete. There are two ways of finding tiprev
for branchcache (both are in use): looking at input data for update() and
looking at computed heads after update(). Previously, repo tip would be
tiprev of the branchcache. With this patch, an obsolete revision can no
longer be tiprev. And depending on what way we use for finding tiprev (input
data vs computed heads) we'll get a different result. This is relevant when
recomputing cache key from cache contents, and may lead to updating cache for
obsolete revisions multiple times (not from scratch, because it still would
be considered valid for a subset of revisions in the repo).
- If all commits on a branch are obsolete, the branchcache will include that
branch, but the list of heads will be empty (that's why there's now `if not
heads` when recomputing tiprev/tipnode from cache contents). Having an entry
for every branch is currently required for notify extension (and
test-notify.t to pass), because notify doesn't handle revsets in its
subscription config very well and will throw an error if e.g. a branch
doesn't exist.
- Cloning static HTTP repos may try to stat() a non-existent obsstore file. The
issue is that we now care about obsolescence during clone, but statichttpvfs
doesn't implement a stat method, so a regular vfs.stat() is used, and it
assumes that file is local and calls os.stat(). During a clone, we're trying
to stat() .hg/store/obsstore, but in static HTTP case we provide a literal
URL to the obsstore file on the remote as if it were a local file path. On
windows it actually results in a failure in test-static-http.t.
The first issue is going to be addressed in a series dedicated to making sure
branchcache is properly and timely written on disk (it wasn't perfect even
before this patch, but there aren't enough tests to demonstrate that). The
second issue will be addressed in a future patch for notify extension that will
make it not raise an exception if a branch doesn't exist. And the third one was
partially addressed in the previous patch in this series and will be properly
fixed in a future patch when this series is accepted.
filteredhash() grows a keyword argument to make sure that branchcache is also
invalidated when there are new obsolete revisions in its repo view. This way
the on-disk cache format is unchanged and compatible between versions (although
it will obviously be recomputed when switching versions before/after this patch
and the repo has obsolete revisions).
There's one test that uses plain `hg up` without arguments while updated to a
pruned commit. To make this test pass, simply return current working directory
parent. Later in this series this code will be replaced by what prune command
does: updating to the closest non-obsolete ancestor.
Test changes:
test-branch-change.t: update branch head and cache update message. The head of
default listed in hg heads is changed because revision 2 was rewritten as 7,
and 1 is the closest ancestor on the same branch, so it's the head of default
now.
The cache invalidation message appears now because of the cache hash change,
since we're now accounting for obsolete revisions. Here's some context:
"served.hidden" repo filter means everything is visible (no filtered
revisions), so before this series branch2-served.hidden file would not contain
any cache hash, only revnum and node. Now it also has a hash when there are
obsolete changesets in the repo. The command that the message appears for is
changing branch of 5 and 6, which are now obsolete, so the cache hash changes.
In general, when cache is simply out-of-date, it can be updated using the old
version as a base. But if cache hash differs, then the cache for that
particular repo filter is recomputed (at least with the current
implementation). This is what happens here.
test-obsmarker-template.t: the pull reports 2 heads changed, but after that the
repo correctly sees only 1. The new message could be better, but it's still an
improvement over the previous one where hg pull suggested merging with an
obsolete revision.
test-obsolete.t: we can see these revisions in hg log --hidden, but they
shouldn't be considered heads even with --hidden.
test-rebase-obsolete{,2}.t: there were new heads created previously after
making new orphan changesets, but they weren't detected. Now we are properly
detecting and reporting them.
test-rebase-obsolete4.t: there's only one head now because the other head is
pruned and was falsely reported before.
test-static-http.t: add obsstore to the list of requested files. This file
doesn't exist on the remotes, but clients want it anyway (they get 404). This
is fine, because there are other nonexistent files that clients request, like
.hg/bookmarks or .hg/cache/tags2-served.
Differential Revision: https://phab.mercurial-scm.org/D12097
author | Anton Shestakov <av6@dwimlabs.net> |
---|---|
date | Fri, 07 Jan 2022 11:53:23 +0300 |
parents | d4ba4d51f85f |
children | 6000f5b25c9b |
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# lock.py - simple advisory locking scheme for mercurial # # Copyright 2005, 2006 Olivia Mackall <olivia@selenic.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import import contextlib import errno import os import signal import socket import time import warnings from .i18n import _ from .pycompat import getattr from . import ( encoding, error, pycompat, util, ) from .utils import procutil def _getlockprefix(): """Return a string which is used to differentiate pid namespaces It's useful to detect "dead" processes and remove stale locks with confidence. Typically it's just hostname. On modern linux, we include an extra Linux-specific pid namespace identifier. """ result = encoding.strtolocal(socket.gethostname()) if pycompat.sysplatform.startswith(b'linux'): try: result += b'/%x' % os.stat(b'/proc/self/ns/pid').st_ino except OSError as ex: if ex.errno not in (errno.ENOENT, errno.EACCES, errno.ENOTDIR): raise return result @contextlib.contextmanager def _delayedinterrupt(): """Block signal interrupt while doing something critical This makes sure that the code block wrapped by this context manager won't be interrupted. For Windows developers: It appears not possible to guard time.sleep() from CTRL_C_EVENT, so please don't use time.sleep() to test if this is working. """ assertedsigs = [] blocked = False orighandlers = {} def raiseinterrupt(num): if num == getattr(signal, 'SIGINT', None) or num == getattr( signal, 'CTRL_C_EVENT', None ): raise KeyboardInterrupt else: raise error.SignalInterrupt def catchterm(num, frame): if blocked: assertedsigs.append(num) else: raiseinterrupt(num) try: # save handlers first so they can be restored even if a setup is # interrupted between signal.signal() and orighandlers[] =. for name in [ b'CTRL_C_EVENT', b'SIGINT', b'SIGBREAK', b'SIGHUP', b'SIGTERM', ]: num = getattr(signal, name, None) if num and num not in orighandlers: orighandlers[num] = signal.getsignal(num) try: for num in orighandlers: signal.signal(num, catchterm) except ValueError: pass # in a thread? no luck blocked = True yield finally: # no simple way to reliably restore all signal handlers because # any loops, recursive function calls, except blocks, etc. can be # interrupted. so instead, make catchterm() raise interrupt. blocked = False try: for num, handler in orighandlers.items(): signal.signal(num, handler) except ValueError: pass # in a thread? # re-raise interrupt exception if any, which may be shadowed by a new # interrupt occurred while re-raising the first one if assertedsigs: raiseinterrupt(assertedsigs[0]) def trylock(ui, vfs, lockname, timeout, warntimeout, *args, **kwargs): """return an acquired lock or raise an a LockHeld exception This function is responsible to issue warnings and or debug messages about the held lock while trying to acquires it.""" def printwarning(printer, locker): """issue the usual "waiting on lock" message through any channel""" # show more details for new-style locks if b':' in locker: host, pid = locker.split(b":", 1) msg = _( b"waiting for lock on %s held by process %r on host %r\n" ) % ( pycompat.bytestr(l.desc), pycompat.bytestr(pid), pycompat.bytestr(host), ) else: msg = _(b"waiting for lock on %s held by %r\n") % ( l.desc, pycompat.bytestr(locker), ) printer(msg) l = lock(vfs, lockname, 0, *args, dolock=False, **kwargs) debugidx = 0 if (warntimeout and timeout) else -1 warningidx = 0 if not timeout: warningidx = -1 elif warntimeout: warningidx = warntimeout delay = 0 while True: try: l._trylock() break except error.LockHeld as inst: if delay == debugidx: printwarning(ui.debug, inst.locker) if delay == warningidx: printwarning(ui.warn, inst.locker) if timeout <= delay: raise error.LockHeld( errno.ETIMEDOUT, inst.filename, l.desc, inst.locker ) time.sleep(1) delay += 1 l.delay = delay if l.delay: if 0 <= warningidx <= l.delay: ui.warn(_(b"got lock after %d seconds\n") % l.delay) else: ui.debug(b"got lock after %d seconds\n" % l.delay) if l.acquirefn: l.acquirefn() return l class lock(object): """An advisory lock held by one process to control access to a set of files. Non-cooperating processes or incorrectly written scripts can ignore Mercurial's locking scheme and stomp all over the repository, so don't do that. Typically used via localrepository.lock() to lock the repository store (.hg/store/) or localrepository.wlock() to lock everything else under .hg/.""" # lock is symlink on platforms that support it, file on others. # symlink is used because create of directory entry and contents # are atomic even over nfs. # old-style lock: symlink to pid # new-style lock: symlink to hostname:pid _host = None def __init__( self, vfs, fname, timeout=-1, releasefn=None, acquirefn=None, desc=None, signalsafe=True, dolock=True, ): self.vfs = vfs self.f = fname self.held = 0 self.timeout = timeout self.releasefn = releasefn self.acquirefn = acquirefn self.desc = desc if signalsafe: self._maybedelayedinterrupt = _delayedinterrupt else: self._maybedelayedinterrupt = util.nullcontextmanager self.postrelease = [] self.pid = self._getpid() if dolock: self.delay = self.lock() if self.acquirefn: self.acquirefn() def __enter__(self): return self def __exit__(self, exc_type, exc_value, exc_tb): success = all(a is None for a in (exc_type, exc_value, exc_tb)) self.release(success=success) def __del__(self): if self.held: warnings.warn( "use lock.release instead of del lock", category=DeprecationWarning, stacklevel=2, ) # ensure the lock will be removed # even if recursive locking did occur self.held = 1 self.release() def _getpid(self): # wrapper around procutil.getpid() to make testing easier return procutil.getpid() def lock(self): timeout = self.timeout while True: try: self._trylock() return self.timeout - timeout except error.LockHeld as inst: if timeout != 0: time.sleep(1) if timeout > 0: timeout -= 1 continue raise error.LockHeld( errno.ETIMEDOUT, inst.filename, self.desc, inst.locker ) def _trylock(self): if self.held: self.held += 1 return if lock._host is None: lock._host = _getlockprefix() lockname = b'%s:%d' % (lock._host, self.pid) retry = 5 while not self.held and retry: retry -= 1 try: with self._maybedelayedinterrupt(): self.vfs.makelock(lockname, self.f) self.held = 1 except (OSError, IOError) as why: if why.errno == errno.EEXIST: locker = self._readlock() if locker is None: continue locker = self._testlock(locker) if locker is not None: raise error.LockHeld( errno.EAGAIN, self.vfs.join(self.f), self.desc, locker, ) else: raise error.LockUnavailable( why.errno, why.strerror, why.filename, self.desc ) if not self.held: # use empty locker to mean "busy for frequent lock/unlock # by many processes" raise error.LockHeld( errno.EAGAIN, self.vfs.join(self.f), self.desc, b"" ) def _readlock(self): """read lock and return its value Returns None if no lock exists, pid for old-style locks, and host:pid for new-style locks. """ try: return self.vfs.readlock(self.f) except (OSError, IOError) as why: if why.errno == errno.ENOENT: return None raise def _lockshouldbebroken(self, locker): if locker is None: return False try: host, pid = locker.split(b":", 1) except ValueError: return False if host != lock._host: return False try: pid = int(pid) except ValueError: return False if procutil.testpid(pid): return False return True 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): locker = self._readlock() if not self._lockshouldbebroken(locker): return locker self.vfs.unlink(self.f) except error.LockError: return locker def testlock(self): """return id of locker if lock is valid, else None. If old-style lock, we cannot tell what machine locker is on. with new-style lock, if locker is on this machine, we can see if locker is alive. If locker is on this machine but not alive, we can safely break lock. The lock file is only deleted when None is returned. """ locker = self._readlock() return self._testlock(locker) def release(self, success=True): """release the lock and execute callback function if any If the lock has been acquired multiple times, the actual release is delayed to the last release call.""" if self.held > 1: self.held -= 1 elif self.held == 1: self.held = 0 if self._getpid() != self.pid: # we forked, and are not the parent return try: if self.releasefn: self.releasefn() finally: try: self.vfs.unlink(self.f) except OSError: pass # The postrelease functions typically assume the lock is not held # at all. for callback in self.postrelease: callback(success) # Prevent double usage and help clear cycles. self.postrelease = None def release(*locks): for lock in locks: if lock is not None: lock.release()