view mercurial/lock.py @ 2439:e8c4f3d3df8c

extend network protocol to stop clients from locking servers

now all repositories have capabilities slot, tuple with list of names.

if 'unbundle' capability present, repo supports push where client does
not need to lock server.  repository classes that have unbundle capability
also have unbundle method.

implemented for ssh now, will be base for push over http.

unbundle protocol acts this way.  server tells client what heads it
has during normal negotiate step.  client starts unbundle by repeat
server's heads back to it.  if server has new heads, abort immediately.
otherwise, transfer changes to server.  once data transferred, server
locks and checks heads again.  if heads same, changes can be added.
else someone else added heads, and server aborts.

if client wants to force server to add heads, sends special heads list of
'force'.

# lock.py - simple locking scheme for mercurial
#
# Copyright 2005 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.

from demandload import *
demandload(globals(), 'errno os socket time util')

class LockException(IOError):
    def __init__(self, errno, strerror, filename, desc):
        IOError.__init__(self, errno, strerror, filename)
        self.desc = desc

class LockHeld(LockException):
    def __init__(self, errno, filename, desc, locker):
        LockException.__init__(self, errno, 'Lock held', filename, desc)
        self.locker = locker

class LockUnavailable(LockException):
    pass

class lock(object):
    # 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

    def __init__(self, file, timeout=-1, releasefn=None, desc=None):
        self.f = file
        self.held = 0
        self.timeout = timeout
        self.releasefn = releasefn
        self.id = None
        self.host = None
        self.pid = None
        self.desc = desc
        self.lock()

    def __del__(self):
        self.release()

    def lock(self):
        timeout = self.timeout
        while 1:
            try:
                self.trylock()
                return 1
            except LockHeld, inst:
                if timeout != 0:
                    time.sleep(1)
                    if timeout > 0:
                        timeout -= 1
                    continue
                raise LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
                               inst.locker)

    def trylock(self):
        if self.id is None:
            self.host = socket.gethostname()
            self.pid = os.getpid()
            self.id = '%s:%s' % (self.host, self.pid)
        while not self.held:
            try:
                util.makelock(self.id, self.f)
                self.held = 1
            except (OSError, IOError), why:
                if why.errno == errno.EEXIST:
                    locker = self.testlock()
                    if locker:
                        raise LockHeld(errno.EAGAIN, self.f, self.desc,
                                       locker)
                else:
                    raise LockUnavailable(why.errno, why.strerror,
                                          why.filename, self.desc)

    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.
        locker = util.readlock(self.f)
        c = locker.find(':')
        if c == -1:
            return locker
        host = locker[:c]
        if host != self.host:
            return locker
        try:
            pid = int(locker[c+1:])
        except:
            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.f + '.break')
            l.trylock()
            os.unlink(self.f)
            l.release()
        except (LockHeld, LockUnavailable):
            return locker

    def release(self):
        if self.held:
            self.held = 0
            if self.releasefn:
                self.releasefn()
            try:
                os.unlink(self.f)
            except: pass