mercurial/lock.py
author Martin Geisler <mg@lazybytes.net>
Sun, 26 Apr 2009 01:08:54 +0200
changeset 8225 46293a0c7e9f
parent 8113 87a1605979e4
child 8312 b87a50b7125c
permissions -rw-r--r--
updated license to be explicit about GPL version 2
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# lock.py - simple 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, incorporated herein by reference.
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import errno, os, socket, time, util, error
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import warnings
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class lock(object):
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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, file, timeout=-1, releasefn=None, desc=None):
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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.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 1:
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            try:
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                self.trylock()
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                return 1
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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, os.getpid())
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        while not self.held:
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            try:
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                util.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, 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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        locker = util.readlock(self.f)
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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:
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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.f + '.break')
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            l.trylock()
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            os.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 release(self):
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        if self.held > 1:
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            self.held -= 1
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        elif self.held is 1:
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            self.held = 0
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            if self.releasefn:
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                self.releasefn()
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            try:
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                os.unlink(self.f)
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            except: pass
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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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