~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005-2011 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

from bzrlib.lazy_import import lazy_import

lazy_import(globals(), """

import warnings

from bzrlib import (

    counted_lock,

    errors,

    lock,

    osutils,

    transactions,

    urlutils,

    )

""")

from bzrlib.decorators import (

    only_raises,

    )

# XXX: The tracking here of lock counts and whether the lock is held is

# somewhat redundant with what's done in LockDir; the main difference is that

# LockableFiles permits reentrancy.

class _LockWarner(object):

    """Hold a counter for a lock and warn if GCed while the count is >= 1.

    This is separate from LockableFiles because putting a __del__ on

    LockableFiles can result in uncollectable cycles.

    """

    def __init__(self, repr):

        self.lock_count = 0

        self.repr = repr

    def __del__(self):

        if self.lock_count >= 1:

            # There should have been a try/finally to unlock this.

            warnings.warn("%r was gc'd while locked" % self.repr)

class LockableFiles(object):

    """Object representing a set of related files locked within the same scope.

    This coordinates access to the lock along with providing a transaction.

    LockableFiles manage a lock count and can be locked repeatedly by

    a single caller.  (The underlying lock implementation generally does not

    support this.)

    Instances of this class are often called control_files.

    This class is now deprecated; code should move to using the Transport

    directly for file operations and using the lock or CountedLock for

    locking.

    :ivar _lock: The real underlying lock (e.g. a LockDir)

    :ivar _counted_lock: A lock decorated with a semaphore, so that it 

        can be re-entered.

    """

    # _lock_mode: None, or 'r' or 'w'

    # _lock_count: If _lock_mode is true, a positive count of the number of

    # times the lock has been taken *by this process*.

    def __init__(self, transport, lock_name, lock_class):

        """Create a LockableFiles group

        :param transport: Transport pointing to the directory holding the

            control files and lock.

        :param lock_name: Name of the lock guarding these files.

        :param lock_class: Class of lock strategy to use: typically

            either LockDir or TransportLock.

        """

        self._transport = transport

        self.lock_name = lock_name

        self._transaction = None

        self._lock_mode = None

        self._lock_warner = _LockWarner(repr(self))

        self._find_modes()

        esc_name = self._escape(lock_name)

        self._lock = lock_class(transport, esc_name,

                                file_modebits=self._file_mode,

                                dir_modebits=self._dir_mode)

        self._counted_lock = counted_lock.CountedLock(self._lock)

    def create_lock(self):

        """Create the lock.

        This should normally be called only when the LockableFiles directory

        is first created on disk.

        """

        self._lock.create(mode=self._dir_mode)

    def __repr__(self):

        return '%s(%r)' % (self.__class__.__name__,

                           self._transport)

    def __str__(self):

        return 'LockableFiles(%s, %s)' % (self.lock_name, self._transport.base)

    def break_lock(self):

        """Break the lock of this lockable files group if it is held.

        The current ui factory will be used to prompt for user conformation.

        """

        self._lock.break_lock()

    def _escape(self, file_or_path):

        """DEPRECATED: Do not use outside this class"""

        if not isinstance(file_or_path, basestring):

            file_or_path = '/'.join(file_or_path)

        if file_or_path == '':

            return u''

        return urlutils.escape(osutils.safe_unicode(file_or_path))

    def _find_modes(self):

        """Determine the appropriate modes for files and directories.

        :deprecated: Replaced by BzrDir._find_creation_modes.

        """

        # XXX: The properties created by this can be removed or deprecated

        # once all the _get_text_store methods etc no longer use them.

        # -- mbp 20080512

        try:

            st = self._transport.stat('.')

        except errors.TransportNotPossible:

            self._dir_mode = 0755

            self._file_mode = 0644

        else:

            # Check the directory mode, but also make sure the created

            # directories and files are read-write for this user. This is

            # mostly a workaround for filesystems which lie about being able to

            # write to a directory (cygwin & win32)

            self._dir_mode = (st.st_mode & 07777) | 00700

            # Remove the sticky and execute bits for files

            self._file_mode = self._dir_mode & ~07111

    def leave_in_place(self):

        """Set this LockableFiles to not clear the physical lock on unlock."""

        self._lock.leave_in_place()

    def dont_leave_in_place(self):

        """Set this LockableFiles to clear the physical lock on unlock."""

        self._lock.dont_leave_in_place()

    def lock_write(self, token=None):

        """Lock this group of files for writing.

        :param token: if this is already locked, then lock_write will fail

            unless the token matches the existing lock.

        :returns: a token if this instance supports tokens, otherwise None.

        :raises TokenLockingNotSupported: when a token is given but this

            instance doesn't support using token locks.

        :raises MismatchedToken: if the specified token doesn't match the token

            of the existing lock.

        A token should be passed in if you know that you have locked the object

        some other way, and need to synchronise this object's state with that

        fact.

        """

        # TODO: Upgrade locking to support using a Transport,

        # and potentially a remote locking protocol

        if self._lock_mode:

            if self._lock_mode != 'w' or not self.get_transaction().writeable():

                raise errors.ReadOnlyError(self)

            self._lock.validate_token(token)

            self._lock_warner.lock_count += 1

            return self._token_from_lock

        else:

            token_from_lock = self._lock.lock_write(token=token)

            #traceback.print_stack()

            self._lock_mode = 'w'

            self._lock_warner.lock_count = 1

            self._set_write_transaction()

            self._token_from_lock = token_from_lock

            return token_from_lock

    def lock_read(self):

        if self._lock_mode:

            if self._lock_mode not in ('r', 'w'):

                raise ValueError("invalid lock mode %r" % (self._lock_mode,))

            self._lock_warner.lock_count += 1

        else:

            self._lock.lock_read()

            #traceback.print_stack()

            self._lock_mode = 'r'

            self._lock_warner.lock_count = 1

            self._set_read_transaction()

    def _set_read_transaction(self):

        """Setup a read transaction."""

        self._set_transaction(transactions.ReadOnlyTransaction())

        # 5K may be excessive, but hey, its a knob.

        self.get_transaction().set_cache_size(5000)

    def _set_write_transaction(self):

        """Setup a write transaction."""

        self._set_transaction(transactions.WriteTransaction())

    @only_raises(errors.LockNotHeld, errors.LockBroken)

    def unlock(self):

        if not self._lock_mode:

            return lock.cant_unlock_not_held(self)

        if self._lock_warner.lock_count > 1:

            self._lock_warner.lock_count -= 1

        else:

            #traceback.print_stack()

            self._finish_transaction()

            try:

                self._lock.unlock()

            finally:

                self._lock_mode = self._lock_warner.lock_count = None

    @property

    def _lock_count(self):

        return self._lock_warner.lock_count

    def is_locked(self):

        """Return true if this LockableFiles group is locked"""

        return self._lock_warner.lock_count >= 1

    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._lock.peek() is not None

        except NotImplementedError:

            return False

    def get_transaction(self):

        """Return the current active transaction.

        If no transaction is active, this returns a passthrough object

        for which all data is immediately flushed and no caching happens.

        """

        if self._transaction is None:

            return transactions.PassThroughTransaction()

        else:

            return self._transaction

    def _set_transaction(self, new_transaction):

        """Set a new active transaction."""

        if self._transaction is not None:

            raise errors.LockError('Branch %s is in a transaction already.' %

                                   self)

        self._transaction = new_transaction

    def _finish_transaction(self):

        """Exit the current transaction."""

        if self._transaction is None:

            raise errors.LockError('Branch %s is not in a transaction' %

                                   self)

        transaction = self._transaction

        self._transaction = None

        transaction.finish()

class TransportLock(object):

    """Locking method which uses transport-dependent locks.

    On the local filesystem these transform into OS-managed locks.

    These do not guard against concurrent access via different

    transports.

    This is suitable for use only in WorkingTrees (which are at present

    always local).

    """

    def __init__(self, transport, escaped_name, file_modebits, dir_modebits):

        self._transport = transport

        self._escaped_name = escaped_name

        self._file_modebits = file_modebits

        self._dir_modebits = dir_modebits

    def break_lock(self):

        raise NotImplementedError(self.break_lock)

    def leave_in_place(self):

        raise NotImplementedError(self.leave_in_place)

    def dont_leave_in_place(self):

        raise NotImplementedError(self.dont_leave_in_place)

    def lock_write(self, token=None):

        if token is not None:

            raise errors.TokenLockingNotSupported(self)

        self._lock = self._transport.lock_write(self._escaped_name)

    def lock_read(self):

        self._lock = self._transport.lock_read(self._escaped_name)

    def unlock(self):

        self._lock.unlock()

        self._lock = None

    def peek(self):

        raise NotImplementedError()

    def create(self, mode=None):

        """Create lock mechanism"""

        # for old-style locks, create the file now

        self._transport.put_bytes(self._escaped_name, '',

                            mode=self._file_modebits)

    def validate_token(self, token):

        if token is not None:

            raise errors.TokenLockingNotSupported(self)