~bzr-pqm/bzr/bzr.dev : contents of bzrlib/counted

~bzr-pqm/bzr/bzr.dev : (revision 4665.5.18)

# Copyright (C) 2007, 2008 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Counted lock class"""


from bzrlib import (
    errors,
    )


class CountedLock(object):
    """Decorator around a lock that makes it reentrant.

    This can be used with any object that provides a basic Lock interface,
    including LockDirs and OS file locks.

    :ivar _token: While a write lock is held, this is the token 
        for it.
    """

    def __init__(self, real_lock):
        self._real_lock = real_lock
        self._lock_mode = None
        self._lock_count = 0

    def __repr__(self):
        return "%s(%r)" % (self.__class__.__name__,
            self._real_lock)

    def break_lock(self):
        self._real_lock.break_lock()
        self._lock_mode = None
        self._lock_count = 0

    def get_physical_lock_status(self):
        """Return physical lock status.

        Returns true if a lock is held on the transport. If no lock is held, or
        the underlying locking mechanism does not support querying lock
        status, false is returned.
        """
        try:
            return self._real_lock.peek() is not None
        except NotImplementedError:
            return False

    def is_locked(self):
        return self._lock_mode is not None

    def lock_read(self):
        """Acquire the lock in read mode.

        If the lock is already held in either read or write mode this
        increments the count and succeeds.  If the lock is not already held,
        it is taken in read mode.
        """
        if self._lock_mode:
            self._lock_count += 1
        else:
            self._real_lock.lock_read()
            self._lock_count = 1
            self._lock_mode = 'r'

    def lock_write(self, token=None):
        """Acquire the lock in write mode.

        If the lock was originally acquired in read mode this will fail.

        :param token: If given and the lock is already held, 
            then validate that we already hold the real
            lock with this token.

        :returns: The token from the underlying lock.
        """
        if self._lock_count == 0:
            self._token = self._real_lock.lock_write(token=token)
            self._lock_mode = 'w'
            self._lock_count += 1
            return self._token
        elif self._lock_mode != 'w':
            raise errors.ReadOnlyError(self)
        else:
            self._real_lock.validate_token(token)
            self._lock_count += 1
            return self._token

    def unlock(self):
        if self._lock_count == 0:
            raise errors.LockNotHeld(self)
        elif self._lock_count == 1:
            # these are decremented first; if we fail to unlock the most
            # reasonable assumption is that we still don't have the lock
            # anymore
            self._lock_mode = None
            self._lock_count -= 1
            self._real_lock.unlock()
        else:
            self._lock_count -= 1

3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	1	# Copyright (C) 2007, 2008 Canonical Ltd
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	2	#
	3	# This program is free software; you can redistribute it and/or modify
	4	# it under the terms of the GNU General Public License as published by
	5	# the Free Software Foundation; either version 2 of the License, or
	6	# (at your option) any later version.
	7	#
	8	# This program is distributed in the hope that it will be useful,
	9	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	10	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	11	# GNU General Public License for more details.
	12	#
	13	# You should have received a copy of the GNU General Public License
	14	# along with this program; if not, write to the Free Software
4183.7.1 by Sabin Iacob update FSF mailing address	15	# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	16
	17	"""Counted lock class"""
	18
	19
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	20	from bzrlib import (
	21	errors,
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	22	)
	23
	24
	25	class CountedLock(object):
	26	"""Decorator around a lock that makes it reentrant.
	27
	28	This can be used with any object that provides a basic Lock interface,
	29	including LockDirs and OS file locks.
3407.2.19 by Martin Pool CountedLock should manage lock tokens	30
	31	:ivar _token: While a write lock is held, this is the token
	32	for it.
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	33	"""
	34
	35	def __init__(self, real_lock):
	36	self._real_lock = real_lock
	37	self._lock_mode = None
	38	self._lock_count = 0
	39
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	40	def __repr__(self):
	41	return "%s(%r)" % (self.__class__.__name__,
	42	self._real_lock)
	43
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	44	def break_lock(self):
	45	self._real_lock.break_lock()
	46	self._lock_mode = None
	47	self._lock_count = 0
	48
4570.3.5 by Martin Pool Add CountedLock.get_physical_lock_status	49	def get_physical_lock_status(self):
	50	"""Return physical lock status.
	51
	52	Returns true if a lock is held on the transport. If no lock is held, or
	53	the underlying locking mechanism does not support querying lock
	54	status, false is returned.
	55	"""
	56	try:
	57	return self._real_lock.peek() is not None
	58	except NotImplementedError:
	59	return False
	60
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	61	def is_locked(self):
	62	return self._lock_mode is not None
	63
	64	def lock_read(self):
	65	"""Acquire the lock in read mode.
	66
	67	If the lock is already held in either read or write mode this
	68	increments the count and succeeds. If the lock is not already held,
	69	it is taken in read mode.
	70	"""
	71	if self._lock_mode:
	72	self._lock_count += 1
	73	else:
	74	self._real_lock.lock_read()
	75	self._lock_count = 1
	76	self._lock_mode = 'r'
	77
3407.2.20 by Martin Pool Add lock token support to CountedLock	78	def lock_write(self, token=None):
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	79	"""Acquire the lock in write mode.
	80
	81	If the lock was originally acquired in read mode this will fail.
3407.2.19 by Martin Pool CountedLock should manage lock tokens	82
3407.2.20 by Martin Pool Add lock token support to CountedLock	83	:param token: If given and the lock is already held,
	84	then validate that we already hold the real
	85	lock with this token.
	86
3407.2.19 by Martin Pool CountedLock should manage lock tokens	87	:returns: The token from the underlying lock.
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	88	"""
	89	if self._lock_count == 0:
3407.2.20 by Martin Pool Add lock token support to CountedLock	90	self._token = self._real_lock.lock_write(token=token)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	91	self._lock_mode = 'w'
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	92	self._lock_count += 1
3468.3.2 by Martin Pool merge trunk	93	return self._token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	94	elif self._lock_mode != 'w':
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	95	raise errors.ReadOnlyError(self)
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	96	else:
	97	self._real_lock.validate_token(token)
	98	self._lock_count += 1
3468.3.4 by Martin Pool CountedLock.lock_write should return existing known token	99	return self._token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	100
	101	def unlock(self):
	102	if self._lock_count == 0:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	103	raise errors.LockNotHeld(self)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	104	elif self._lock_count == 1:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	105	# these are decremented first; if we fail to unlock the most
	106	# reasonable assumption is that we still don't have the lock
	107	# anymore
	108	self._lock_mode = None
	109	self._lock_count -= 1
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	110	self._real_lock.unlock()
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	111	else:
	112	self._lock_count -= 1