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  • Committer: Ian Clatworthy
  • Date: 2008-03-27 07:51:10 UTC
  • mto: (3311.1.1 ianc-integration)
  • mto: This revision was merged to the branch mainline in revision 3312.
  • Revision ID: ian.clatworthy@canonical.com-20080327075110-afgd7x03ybju06ez
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bzrlib/counted_lock.py
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# Copyright (C) 2007, 2008 Canonical Ltd
 
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# Copyright (C) 2007 Canonical Ltd
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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"""Counted lock class"""
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from bzrlib import (
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    errors,
 
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from bzrlib.errors import (
 
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    LockError,
 
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    ReadOnlyError,
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    )
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# TODO: Pass through lock tokens on lock_write and read, and return them...
 
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#
 
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# TODO: Allow upgrading read locks to write?  Conceptually difficult.
 
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class CountedLock(object):
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    """Decorator around a lock that makes it reentrant.
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        self._lock_mode = None
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        self._lock_count = 0
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    def __repr__(self):
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        return "%s(%r)" % (self.__class__.__name__,
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            self._real_lock)
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    def break_lock(self):
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        self._real_lock.break_lock()
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        self._lock_mode = None
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        it is taken in read mode.
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        """
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        if self._lock_mode:
 
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            assert self._lock_mode in ('r', 'w'), \
 
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                   "invalid lock mode %r" % self._lock_mode
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            self._lock_count += 1
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        else:
 
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            assert self._lock_count == 0
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            self._real_lock.lock_read()
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            self._lock_count = 1
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            self._lock_mode = 'r'
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    def lock_write(self, token=None):
 
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    def lock_write(self):
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        """Acquire the lock in write mode.
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        If the lock was originally acquired in read mode this will fail.
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        :param token: If non-None, reacquire the lock using this token.
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        """
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        if self._lock_count == 0:
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            return_token = self._real_lock.lock_write(token)
 
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            assert self._lock_mode is None
 
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            self._real_lock.lock_write()
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            self._lock_mode = 'w'
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            self._lock_count += 1
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            return return_token
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        elif self._lock_mode != 'w':
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            raise errors.ReadOnlyError(self)
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        else:
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            self._real_lock.validate_token(token)
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            self._lock_count += 1
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            return token
 
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            raise ReadOnlyError(self)
 
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        self._lock_count += 1
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    def unlock(self):
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        if self._lock_count == 0:
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            raise errors.LockNotHeld(self)
 
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            raise LockError("%s not locked" % (self,))
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        elif self._lock_count == 1:
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            # these are decremented first; if we fail to unlock the most
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            # reasonable assumption is that we still don't have the lock
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            # anymore
 
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            self._real_lock.unlock()
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            self._lock_mode = None
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            self._lock_count -= 1
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            self._real_lock.unlock()
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        else:
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            self._lock_count -= 1
 
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        self._lock_count -= 1