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4a04cef0a1
This is part of a series that will allow locks to be inherited by subprocesses in limited circumstances. This patch enables the logic introduced in previous patches.
232 lines
7.5 KiB
Python
232 lines
7.5 KiB
Python
# 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 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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error,
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util,
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)
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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, 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.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 __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 os.getpid() to make testing easier
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return os.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 = socket.gethostname()
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lockname = '%s:%s' % (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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# 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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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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def prepinherit(self):
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"""prepare for the lock to be inherited by a Mercurial subprocess
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Returns a string that will be recognized by the lock in the
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subprocess. Communicating this string to the subprocess needs to be done
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separately -- 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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'prepinherit 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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'prepinherit cannot be called while lock is already inherited')
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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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return lockname
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def reacquire(self):
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if not self._inherited:
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raise error.LockInheritanceContractViolation(
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'reacquire can only be called after prepinherit')
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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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for callback in self.postrelease:
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callback()
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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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