bundle2: move part iterator a separate class
Currently, the part iterator logic is tightly coupled with the part handling
logic, which means it's hard to replace the part handling logic without
duplicating the part iterator bits.
In a future diff we'll want to be able to replace all part handling, so let's
begin refactoring the part iterator logic to it's own class.
Differential Revision: https://phab.mercurial-scm.org/D703
# lock.py - simple advisory locking scheme for mercurial
#
# Copyright 2005, 2006 Matt Mackall <mpm@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 socket
import time
import warnings
from . import (
encoding,
error,
pycompat,
util,
)
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 = socket.gethostname()
if pycompat.ispy3:
result = result.encode(pycompat.sysstr(encoding.encoding), 'replace')
if pycompat.sysplatform.startswith('linux'):
try:
result += '/%x' % os.stat('/proc/self/ns/pid').st_ino
except OSError as ex:
if ex.errno not in (errno.ENOENT, errno.EACCES, errno.ENOTDIR):
raise
return result
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, file, timeout=-1, releasefn=None, acquirefn=None,
desc=None, inheritchecker=None, parentlock=None):
self.vfs = vfs
self.f = file
self.held = 0
self.timeout = timeout
self.releasefn = releasefn
self.acquirefn = acquirefn
self.desc = desc
self._inheritchecker = inheritchecker
self.parentlock = parentlock
self._parentheld = False
self._inherited = False
self.postrelease = []
self.pid = self._getpid()
self.delay = self.lock()
if self.acquirefn:
self.acquirefn()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, exc_tb):
self.release()
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 util.getpid() to make testing easier
return util.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 = '%s:%d' % (lock._host, self.pid)
retry = 5
while not self.held and retry:
retry -= 1
try:
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
# special case where a parent process holds the lock -- this
# is different from the pid being different because we do
# want the unlock and postrelease functions to be called,
# but the lockfile to not be removed.
if locker == self.parentlock:
self._parentheld = True
self.held = 1
return
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, "")
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 _testlock(self, locker):
if locker is None:
return None
try:
host, pid = locker.split(":", 1)
except ValueError:
return locker
if host != lock._host:
return locker
try:
pid = int(pid)
except ValueError:
return locker
if util.testpid(pid):
return locker
# if locker dead, break lock. must do this with another lock
# held, or can race and break valid lock.
try:
l = lock(self.vfs, self.f + '.break', timeout=0)
self.vfs.unlink(self.f)
l.release()
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)
@contextlib.contextmanager
def inherit(self):
"""context for the lock to be inherited by a Mercurial subprocess.
Yields a string that will be recognized by the lock in the subprocess.
Communicating this string to the subprocess needs to be done separately
-- typically by an environment variable.
"""
if not self.held:
raise error.LockInheritanceContractViolation(
'inherit can only be called while lock is held')
if self._inherited:
raise error.LockInheritanceContractViolation(
'inherit cannot be called while lock is already inherited')
if self._inheritchecker is not None:
self._inheritchecker()
if self.releasefn:
self.releasefn()
if self._parentheld:
lockname = self.parentlock
else:
lockname = '%s:%s' % (lock._host, self.pid)
self._inherited = True
try:
yield lockname
finally:
if self.acquirefn:
self.acquirefn()
self._inherited = False
def release(self):
"""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:
if not self._parentheld:
try:
self.vfs.unlink(self.f)
except OSError:
pass
# The postrelease functions typically assume the lock is not held
# at all.
if not self._parentheld:
for callback in self.postrelease:
callback()
# Prevent double usage and help clear cycles.
self.postrelease = None
def release(*locks):
for lock in locks:
if lock is not None:
lock.release()