branchcache-v3: use more explicit header line
The key-value approach is clearer and gives more rooms to have the format evolve
in a clear way. It also provides extension (like topic) simpler way to extend
the validation scheme.
This is just a small evolution, the V3 format is still a work in progress.
# 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.
import contextlib
import errno
import os
import signal
import socket
import time
import typing
import warnings
from .i18n import _
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 (FileNotFoundError, PermissionError, NotADirectoryError):
pass
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 [
'CTRL_C_EVENT',
'SIGINT',
'SIGBREAK',
'SIGHUP',
'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."""
devel_wait_file = kwargs.pop("devel_wait_sync_file", None)
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 devel_wait_file is not None:
# create the file to signal we are waiting
with open(devel_wait_file, 'w'):
pass
if delay == debugidx:
printwarning(ui.debug, inst.locker)
if delay == warningidx:
printwarning(ui.warn, inst.locker)
if timeout <= delay:
assert isinstance(inst.filename, bytes)
raise error.LockHeld(
errno.ETIMEDOUT,
typing.cast(bytes, 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:
"""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:
assert isinstance(why.filename, bytes)
assert isinstance(why.strerror, str)
raise error.LockUnavailable(
why.errno,
why.strerror,
typing.cast(bytes, 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 FileNotFoundError:
return None
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()