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# lock.py - simple advisory locking scheme for mercurial
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#
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# Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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from __future__ import absolute_import
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import contextlib
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import errno
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import os
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import socket
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import time
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import warnings
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from . import (
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encoding,
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error,
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pycompat,
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util,
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)
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def _getlockprefix():
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"""Return a string which is used to differentiate pid namespaces
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It's useful to detect "dead" processes and remove stale locks with
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confidence. Typically it's just hostname. On modern linux, we include an
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extra Linux-specific pid namespace identifier.
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"""
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result = socket.gethostname()
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if pycompat.ispy3:
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result = result.encode(pycompat.sysstr(encoding.encoding), 'replace')
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if pycompat.sysplatform.startswith('linux'):
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try:
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result += '/%x' % os.stat('/proc/self/ns/pid').st_ino
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except OSError as ex:
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if ex.errno not in (errno.ENOENT, errno.EACCES, errno.ENOTDIR):
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raise
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return result
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class lock(object):
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'''An advisory lock held by one process to control access to a set
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of files. Non-cooperating processes or incorrectly written scripts
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can ignore Mercurial's locking scheme and stomp all over the
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repository, so don't do that.
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Typically used via localrepository.lock() to lock the repository
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store (.hg/store/) or localrepository.wlock() to lock everything
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else under .hg/.'''
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# lock is symlink on platforms that support it, file on others.
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# symlink is used because create of directory entry and contents
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# are atomic even over nfs.
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# old-style lock: symlink to pid
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# new-style lock: symlink to hostname:pid
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_host = None
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def __init__(self, vfs, file, timeout=-1, releasefn=None, acquirefn=None,
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desc=None, inheritchecker=None, parentlock=None):
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self.vfs = vfs
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self.f = file
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self.held = 0
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self.timeout = timeout
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self.releasefn = releasefn
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self.acquirefn = acquirefn
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self.desc = desc
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self._inheritchecker = inheritchecker
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self.parentlock = parentlock
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self._parentheld = False
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self._inherited = False
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self.postrelease = []
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self.pid = self._getpid()
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self.delay = self.lock()
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if self.acquirefn:
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self.acquirefn()
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def __enter__(self):
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return self
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def __exit__(self, exc_type, exc_value, exc_tb):
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self.release()
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def __del__(self):
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if self.held:
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warnings.warn("use lock.release instead of del lock",
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category=DeprecationWarning,
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stacklevel=2)
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# ensure the lock will be removed
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# even if recursive locking did occur
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self.held = 1
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self.release()
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def _getpid(self):
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# wrapper around util.getpid() to make testing easier
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return util.getpid()
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def lock(self):
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timeout = self.timeout
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while True:
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try:
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self._trylock()
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return self.timeout - timeout
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except error.LockHeld as inst:
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if timeout != 0:
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time.sleep(1)
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if timeout > 0:
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timeout -= 1
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continue
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raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
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inst.locker)
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def _trylock(self):
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if self.held:
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self.held += 1
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return
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if lock._host is None:
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lock._host = _getlockprefix()
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lockname = '%s:%d' % (lock._host, self.pid)
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retry = 5
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while not self.held and retry:
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retry -= 1
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try:
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self.vfs.makelock(lockname, self.f)
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self.held = 1
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except (OSError, IOError) as why:
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if why.errno == errno.EEXIST:
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locker = self._readlock()
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if locker is None:
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continue
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# special case where a parent process holds the lock -- this
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# is different from the pid being different because we do
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# want the unlock and postrelease functions to be called,
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# but the lockfile to not be removed.
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if locker == self.parentlock:
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self._parentheld = True
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self.held = 1
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return
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locker = self._testlock(locker)
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if locker is not None:
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raise error.LockHeld(errno.EAGAIN,
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self.vfs.join(self.f), self.desc,
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locker)
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else:
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raise error.LockUnavailable(why.errno, why.strerror,
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why.filename, self.desc)
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if not self.held:
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# use empty locker to mean "busy for frequent lock/unlock
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# by many processes"
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raise error.LockHeld(errno.EAGAIN,
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self.vfs.join(self.f), self.desc, "")
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def _readlock(self):
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"""read lock and return its value
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Returns None if no lock exists, pid for old-style locks, and host:pid
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for new-style locks.
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"""
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try:
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return self.vfs.readlock(self.f)
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except (OSError, IOError) as why:
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if why.errno == errno.ENOENT:
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return None
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raise
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def _testlock(self, locker):
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if locker is None:
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return None
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try:
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host, pid = locker.split(":", 1)
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except ValueError:
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return locker
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if host != lock._host:
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return locker
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try:
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pid = int(pid)
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except ValueError:
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return locker
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if util.testpid(pid):
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return locker
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# if locker dead, break lock. must do this with another lock
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# held, or can race and break valid lock.
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try:
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l = lock(self.vfs, self.f + '.break', timeout=0)
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self.vfs.unlink(self.f)
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l.release()
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except error.LockError:
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return locker
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def testlock(self):
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"""return id of locker if lock is valid, else None.
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If old-style lock, we cannot tell what machine locker is on.
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with new-style lock, if locker is on this machine, we can
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see if locker is alive. If locker is on this machine but
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not alive, we can safely break lock.
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The lock file is only deleted when None is returned.
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"""
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locker = self._readlock()
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return self._testlock(locker)
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@contextlib.contextmanager
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def inherit(self):
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"""context for the lock to be inherited by a Mercurial subprocess.
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Yields a string that will be recognized by the lock in the subprocess.
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Communicating this string to the subprocess needs to be done separately
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-- typically by an environment variable.
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"""
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if not self.held:
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raise error.LockInheritanceContractViolation(
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'inherit can only be called while lock is held')
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if self._inherited:
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raise error.LockInheritanceContractViolation(
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'inherit cannot be called while lock is already inherited')
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if self._inheritchecker is not None:
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self._inheritchecker()
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if self.releasefn:
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self.releasefn()
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if self._parentheld:
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lockname = self.parentlock
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else:
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lockname = '%s:%s' % (lock._host, self.pid)
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self._inherited = True
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try:
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yield lockname
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finally:
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if self.acquirefn:
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self.acquirefn()
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self._inherited = False
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def release(self):
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"""release the lock and execute callback function if any
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If the lock has been acquired multiple times, the actual release is
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delayed to the last release call."""
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if self.held > 1:
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self.held -= 1
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elif self.held == 1:
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self.held = 0
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if self._getpid() != self.pid:
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# we forked, and are not the parent
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return
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try:
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if self.releasefn:
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self.releasefn()
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finally:
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if not self._parentheld:
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try:
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self.vfs.unlink(self.f)
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except OSError:
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pass
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# The postrelease functions typically assume the lock is not held
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# at all.
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if not self._parentheld:
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for callback in self.postrelease:
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callback()
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# Prevent double usage and help clear cycles.
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self.postrelease = None
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def release(*locks):
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for lock in locks:
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if lock is not None:
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lock.release()
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