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

~bzr-pqm/bzr/bzr.dev : (revision 4356)

# 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 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
	49	def is_locked(self):
	50	return self._lock_mode is not None
	51
	52	def lock_read(self):
	53	"""Acquire the lock in read mode.
	54
	55	If the lock is already held in either read or write mode this
	56	increments the count and succeeds. If the lock is not already held,
	57	it is taken in read mode.
	58	"""
	59	if self._lock_mode:
	60	self._lock_count += 1
	61	else:
	62	self._real_lock.lock_read()
	63	self._lock_count = 1
	64	self._lock_mode = 'r'
	65
3407.2.20 by Martin Pool Add lock token support to CountedLock	66	def lock_write(self, token=None):
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	67	"""Acquire the lock in write mode.
	68
	69	If the lock was originally acquired in read mode this will fail.
3407.2.19 by Martin Pool CountedLock should manage lock tokens	70
3407.2.20 by Martin Pool Add lock token support to CountedLock	71	:param token: If given and the lock is already held,
	72	then validate that we already hold the real
	73	lock with this token.
	74
3407.2.19 by Martin Pool CountedLock should manage lock tokens	75	:returns: The token from the underlying lock.
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	76	"""
	77	if self._lock_count == 0:
3407.2.20 by Martin Pool Add lock token support to CountedLock	78	self._token = self._real_lock.lock_write(token=token)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	79	self._lock_mode = 'w'
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	80	self._lock_count += 1
3468.3.2 by Martin Pool merge trunk	81	return self._token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	82	elif self._lock_mode != 'w':
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	83	raise errors.ReadOnlyError(self)
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	84	else:
	85	self._real_lock.validate_token(token)
	86	self._lock_count += 1
3468.3.4 by Martin Pool CountedLock.lock_write should return existing known token	87	return self._token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	88
	89	def unlock(self):
	90	if self._lock_count == 0:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	91	raise errors.LockNotHeld(self)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	92	elif self._lock_count == 1:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	93	# these are decremented first; if we fail to unlock the most
	94	# reasonable assumption is that we still don't have the lock
	95	# anymore
	96	self._lock_mode = None
	97	self._lock_count -= 1
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	98	self._real_lock.unlock()
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	99	else:
	100	self._lock_count -= 1