mercurial/lock.py
author Matt Mackall <mpm@selenic.com>
Mon, 10 Nov 2014 17:29:15 -0600
changeset 23244 18cc87e4375a
parent 23032 f484be02bd35
child 25660 328739ea70c3
permissions -rw-r--r--
merge with stable
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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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import util, error
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import errno, os, socket, time
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import warnings
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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, desc=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.desc = desc
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        self.postrelease  = []
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        self.pid = os.getpid()
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        self.delay = self.lock()
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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 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, 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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        while not self.held:
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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), why:
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                if why.errno == errno.EEXIST:
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                    locker = self.testlock()
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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 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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        try:
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            locker = self.vfs.readlock(self.f)
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        except (OSError, IOError), 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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        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
161
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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 os.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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                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()