/brz/remove-bazaar : contents of bzrlib/counted

: (revision 3640.2.6)

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# 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  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.
    """

    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 non-None, reacquire the lock using this token.
        """
        if self._lock_count == 0:
            return_token = self._real_lock.lock_write(token)
            self._lock_mode = 'w'
            self._lock_count += 1
            return return_token
        elif self._lock_mode != 'w':
            raise errors.ReadOnlyError(self)
        else:
            self._real_lock.validate_token(token)
            self._lock_count += 1
            return 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
	15	# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	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.
	30	"""
	31
	32	def __init__(self, real_lock):
	33	self._real_lock = real_lock
	34	self._lock_mode = None
	35	self._lock_count = 0
	36
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	37	def __repr__(self):
	38	return "%s(%r)" % (self.__class__.__name__,
	39	self._real_lock)
	40
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	41	def break_lock(self):
	42	self._real_lock.break_lock()
	43	self._lock_mode = None
	44	self._lock_count = 0
	45
	46	def is_locked(self):
	47	return self._lock_mode is not None
	48
	49	def lock_read(self):
	50	"""Acquire the lock in read mode.
	51
	52	If the lock is already held in either read or write mode this
	53	increments the count and succeeds. If the lock is not already held,
	54	it is taken in read mode.
	55	"""
	56	if self._lock_mode:
	57	self._lock_count += 1
	58	else:
	59	self._real_lock.lock_read()
	60	self._lock_count = 1
	61	self._lock_mode = 'r'
	62
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	63	def lock_write(self, token=None):
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	64	"""Acquire the lock in write mode.
	65
	66	If the lock was originally acquired in read mode this will fail.
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	67
	68	:param token: If non-None, reacquire the lock using this token.
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	69	"""
	70	if self._lock_count == 0:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	71	return_token = self._real_lock.lock_write(token)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	72	self._lock_mode = 'w'
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	73	self._lock_count += 1
	74	return return_token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	75	elif self._lock_mode != 'w':
3474.1.2 by Martin Pool CountedLock.unlock should raise LockNotHeld if appropriate	76	raise errors.ReadOnlyError(self)
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	77	else:
	78	self._real_lock.validate_token(token)
	79	self._lock_count += 1
	80	return token
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	81
	82	def unlock(self):
	83	if self._lock_count == 0:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	84	raise errors.LockNotHeld(self)
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	85	elif self._lock_count == 1:
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	86	# these are decremented first; if we fail to unlock the most
	87	# reasonable assumption is that we still don't have the lock
	88	# anymore
	89	self._lock_mode = None
	90	self._lock_count -= 1
2475.4.1 by Martin Pool Start adding CountedLock class to partially replace LockableFiles	91	self._real_lock.unlock()
3474.1.3 by Martin Pool CountedLock now handles and tests lock tokens	92	else:
	93	self._lock_count -= 1