~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005-2010 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

"""Locking using OS file locks or file existence.

Note: This method of locking is generally deprecated in favour of LockDir, but

is used to lock local WorkingTrees, and by some old formats.  It's accessed

through Transport.lock_read(), etc.

This module causes two methods, lock() and unlock() to be defined in

any way that works on the current platform.

It is not specified whether these locks are reentrant (i.e. can be

taken repeatedly by a single process) or whether they exclude

different threads in a single process.  That reentrancy is provided by

LockableFiles.

This defines two classes: ReadLock and WriteLock, which can be

implemented in different ways on different platforms.  Both have an

unlock() method.

"""

from __future__ import absolute_import

import contextlib

import errno

import os

import sys

import warnings

from bzrlib import (

    debug,

    errors,

    osutils,

    trace,

    )

from bzrlib.hooks import Hooks

from bzrlib.i18n import gettext

class LockHooks(Hooks):

    def __init__(self):

        Hooks.__init__(self, "bzrlib.lock", "Lock.hooks")

        self.add_hook('lock_acquired',

            "Called with a bzrlib.lock.LockResult when a physical lock is "

            "acquired.", (1, 8))

        self.add_hook('lock_released',

            "Called with a bzrlib.lock.LockResult when a physical lock is "

            "released.", (1, 8))

        self.add_hook('lock_broken',

            "Called with a bzrlib.lock.LockResult when a physical lock is "

            "broken.", (1, 15))

class Lock(object):

    """Base class for locks.

    :cvar hooks: Hook dictionary for operations on locks.

    """

    hooks = LockHooks()

class LockResult(object):

    """Result of an operation on a lock; passed to a hook"""

    def __init__(self, lock_url, details=None):

        """Create a lock result for lock with optional details about the lock."""

        self.lock_url = lock_url

        self.details = details

    def __eq__(self, other):

        return self.lock_url == other.lock_url and self.details == other.details

    def __repr__(self):

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

                             self.lock_url, self.details)

class LogicalLockResult(object):

    """The result of a lock_read/lock_write/lock_tree_write call on lockables.

    :ivar unlock: A callable which will unlock the lock.

    """

    def __init__(self, unlock):

        self.unlock = unlock

    def __repr__(self):

        return "LogicalLockResult(%s)" % (self.unlock)

def cant_unlock_not_held(locked_object):

    """An attempt to unlock failed because the object was not locked.

    This provides a policy point from which we can generate either a warning 

    or an exception.

    """

    # This is typically masking some other error and called from a finally

    # block, so it's useful to have the option not to generate a new error

    # here.  You can use -Werror to make it fatal.  It should possibly also

    # raise LockNotHeld.

    if 'unlock' in debug.debug_flags:

        warnings.warn("%r is already unlocked" % (locked_object,),

            stacklevel=3)

    else:

        raise errors.LockNotHeld(locked_object)

try:

    import fcntl

    have_fcntl = True

except ImportError:

    have_fcntl = False

have_pywin32 = False

have_ctypes_win32 = False

if sys.platform == 'win32':

    import msvcrt

    try:

        import win32file, pywintypes, winerror

        have_pywin32 = True

    except ImportError:

        pass

    try:

        import ctypes

        have_ctypes_win32 = True

    except ImportError:

        pass

class _OSLock(object):

    def __init__(self):

        self.f = None

        self.filename = None

    def _open(self, filename, filemode):

        self.filename = osutils.realpath(filename)

        try:

            self.f = open(self.filename, filemode)

            return self.f

        except IOError, e:

            if e.errno in (errno.EACCES, errno.EPERM):

                raise errors.LockFailed(self.filename, str(e))

            if e.errno != errno.ENOENT:

                raise

            # maybe this is an old branch (before may 2005)

            trace.mutter("trying to create missing lock %r", self.filename)

            self.f = open(self.filename, 'wb+')

            return self.f

    def _clear_f(self):

        """Clear the self.f attribute cleanly."""

        if self.f:

            self.f.close()

            self.f = None

    def unlock(self):

        raise NotImplementedError()

_lock_classes = []

if have_fcntl:

    class _fcntl_FileLock(_OSLock):

        def _unlock(self):

            fcntl.lockf(self.f, fcntl.LOCK_UN)

            self._clear_f()

    class _fcntl_WriteLock(_fcntl_FileLock):

        _open_locks = set()

        def __init__(self, filename):

            super(_fcntl_WriteLock, self).__init__()

            # Check we can grab a lock before we actually open the file.

            self.filename = osutils.realpath(filename)

            if self.filename in _fcntl_WriteLock._open_locks:

                self._clear_f()

                raise errors.LockContention(self.filename)

            if self.filename in _fcntl_ReadLock._open_locks:

                if 'strict_locks' in debug.debug_flags:

                    self._clear_f()

                    raise errors.LockContention(self.filename)

                else:

                    trace.mutter('Write lock taken w/ an open read lock on: %s'

                                 % (self.filename,))

            self._open(self.filename, 'rb+')

            # reserve a slot for this lock - even if the lockf call fails,

            # at this point unlock() will be called, because self.f is set.

            # TODO: make this fully threadsafe, if we decide we care.

            _fcntl_WriteLock._open_locks.add(self.filename)

            try:

                # LOCK_NB will cause IOError to be raised if we can't grab a

                # lock right away.

                fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB)

            except IOError, e:

                if e.errno in (errno.EAGAIN, errno.EACCES):

                    # We couldn't grab the lock

                    self.unlock()

                # we should be more precise about whats a locking

                # error and whats a random-other error

                raise errors.LockContention(self.filename, e)

        def unlock(self):

            _fcntl_WriteLock._open_locks.remove(self.filename)

            self._unlock()

    class _fcntl_ReadLock(_fcntl_FileLock):

        _open_locks = {}

        def __init__(self, filename):

            super(_fcntl_ReadLock, self).__init__()

            self.filename = osutils.realpath(filename)

            if self.filename in _fcntl_WriteLock._open_locks:

                if 'strict_locks' in debug.debug_flags:

                    # We raise before calling _open so we don't need to

                    # _clear_f

                    raise errors.LockContention(self.filename)

                else:

                    trace.mutter('Read lock taken w/ an open write lock on: %s'

                                 % (self.filename,))

            _fcntl_ReadLock._open_locks.setdefault(self.filename, 0)

            _fcntl_ReadLock._open_locks[self.filename] += 1

            self._open(filename, 'rb')

            try:

                # LOCK_NB will cause IOError to be raised if we can't grab a

                # lock right away.

                fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB)

            except IOError, e:

                # we should be more precise about whats a locking

                # error and whats a random-other error

                raise errors.LockContention(self.filename, e)

        def unlock(self):

            count = _fcntl_ReadLock._open_locks[self.filename]

            if count == 1:

                del _fcntl_ReadLock._open_locks[self.filename]

            else:

                _fcntl_ReadLock._open_locks[self.filename] = count - 1

            self._unlock()

        def temporary_write_lock(self):

            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock

            without unlocking the file.

            Otherwise, this will release the read lock, and try to acquire a

            write lock.

            :return: A token which can be used to switch back to a read lock.

            """

            if self.filename in _fcntl_WriteLock._open_locks:

                raise AssertionError('file already locked: %r'

                    % (self.filename,))

            try:

                wlock = _fcntl_TemporaryWriteLock(self)

            except errors.LockError:

                # We didn't unlock, so we can just return 'self'

                return False, self

            return True, wlock

    class _fcntl_TemporaryWriteLock(_OSLock):

        """A token used when grabbing a temporary_write_lock.

        Call restore_read_lock() when you are done with the write lock.

        """

        def __init__(self, read_lock):

            super(_fcntl_TemporaryWriteLock, self).__init__()

            self._read_lock = read_lock

            self.filename = read_lock.filename

            count = _fcntl_ReadLock._open_locks[self.filename]

            if count > 1:

                # Something else also has a read-lock, so we cannot grab a

                # write lock.

                raise errors.LockContention(self.filename)

            if self.filename in _fcntl_WriteLock._open_locks:

                raise AssertionError('file already locked: %r'

                    % (self.filename,))

            # See if we can open the file for writing. Another process might

            # have a read lock. We don't use self._open() because we don't want

            # to create the file if it exists. That would have already been

            # done by _fcntl_ReadLock

            try:

                new_f = open(self.filename, 'rb+')

            except IOError, e:

                if e.errno in (errno.EACCES, errno.EPERM):

                    raise errors.LockFailed(self.filename, str(e))

                raise

            try:

                # LOCK_NB will cause IOError to be raised if we can't grab a

                # lock right away.

                fcntl.lockf(new_f, fcntl.LOCK_EX | fcntl.LOCK_NB)

            except IOError, e:

                # TODO: Raise a more specific error based on the type of error

                raise errors.LockContention(self.filename, e)

            _fcntl_WriteLock._open_locks.add(self.filename)

            self.f = new_f

        def restore_read_lock(self):

            """Restore the original ReadLock."""

            # For fcntl, since we never released the read lock, just release the

            # write lock, and return the original lock.

            fcntl.lockf(self.f, fcntl.LOCK_UN)

            self._clear_f()

            _fcntl_WriteLock._open_locks.remove(self.filename)

            # Avoid reference cycles

            read_lock = self._read_lock

            self._read_lock = None

            return read_lock

    _lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock))

if have_pywin32 and sys.platform == 'win32':

    if os.path.supports_unicode_filenames:

        # for Windows NT/2K/XP/etc

        win32file_CreateFile = win32file.CreateFileW

    else:

        # for Windows 98

        win32file_CreateFile = win32file.CreateFile

    class _w32c_FileLock(_OSLock):

        def _open(self, filename, access, share, cflags, pymode):

            self.filename = osutils.realpath(filename)

            try:

                self._handle = win32file_CreateFile(filename, access, share,

                    None, win32file.OPEN_ALWAYS,

                    win32file.FILE_ATTRIBUTE_NORMAL, None)

            except pywintypes.error, e:

                if e.args[0] == winerror.ERROR_ACCESS_DENIED:

                    raise errors.LockFailed(filename, e)

                if e.args[0] == winerror.ERROR_SHARING_VIOLATION:

                    raise errors.LockContention(filename, e)

                raise

            fd = win32file._open_osfhandle(self._handle, cflags)

            self.f = os.fdopen(fd, pymode)

            return self.f

        def unlock(self):

            self._clear_f()

            self._handle = None

    class _w32c_ReadLock(_w32c_FileLock):

        def __init__(self, filename):

            super(_w32c_ReadLock, self).__init__()

            self._open(filename, win32file.GENERIC_READ,

                win32file.FILE_SHARE_READ, os.O_RDONLY, "rb")

        def temporary_write_lock(self):

            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock

            without unlocking the file.

            Otherwise, this will release the read lock, and try to acquire a

            write lock.

            :return: A token which can be used to switch back to a read lock.

            """

            # I can't find a way to upgrade a read lock to a write lock without

            # unlocking first. So here, we do just that.

            self.unlock()

            try:

                wlock = _w32c_WriteLock(self.filename)

            except errors.LockError:

                return False, _w32c_ReadLock(self.filename)

            return True, wlock

    class _w32c_WriteLock(_w32c_FileLock):

        def __init__(self, filename):

            super(_w32c_WriteLock, self).__init__()

            self._open(filename,

                win32file.GENERIC_READ | win32file.GENERIC_WRITE, 0,

                os.O_RDWR, "rb+")

        def restore_read_lock(self):

            """Restore the original ReadLock."""

            # For win32 we had to completely let go of the original lock, so we

            # just unlock and create a new read lock.

            self.unlock()

            return _w32c_ReadLock(self.filename)

    _lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock))

if have_ctypes_win32:

    from ctypes.wintypes import DWORD, LPCSTR, LPCWSTR

    LPSECURITY_ATTRIBUTES = ctypes.c_void_p # used as NULL no need to declare

    HANDLE = ctypes.c_int # rather than unsigned as in ctypes.wintypes

    if os.path.supports_unicode_filenames:

        _function_name = "CreateFileW"

        LPTSTR = LPCWSTR

    else:

        _function_name = "CreateFileA"

        class LPTSTR(LPCSTR):

            def __new__(cls, obj):

                return LPCSTR.__new__(cls, obj.encode("mbcs"))

    # CreateFile <http://msdn.microsoft.com/en-us/library/aa363858.aspx>

    _CreateFile = ctypes.WINFUNCTYPE(

            HANDLE,                # return value

            LPTSTR,                # lpFileName

            DWORD,                 # dwDesiredAccess

            DWORD,                 # dwShareMode

            LPSECURITY_ATTRIBUTES, # lpSecurityAttributes

            DWORD,                 # dwCreationDisposition

            DWORD,                 # dwFlagsAndAttributes

            HANDLE                 # hTemplateFile

        )((_function_name, ctypes.windll.kernel32))

    INVALID_HANDLE_VALUE = -1

    GENERIC_READ = 0x80000000

    GENERIC_WRITE = 0x40000000

    FILE_SHARE_READ = 1

    OPEN_ALWAYS = 4

    FILE_ATTRIBUTE_NORMAL = 128

    ERROR_ACCESS_DENIED = 5

    ERROR_SHARING_VIOLATION = 32

    class _ctypes_FileLock(_OSLock):

        def _open(self, filename, access, share, cflags, pymode):

            self.filename = osutils.realpath(filename)

            handle = _CreateFile(filename, access, share, None, OPEN_ALWAYS,

                FILE_ATTRIBUTE_NORMAL, 0)

            if handle in (INVALID_HANDLE_VALUE, 0):

                e = ctypes.WinError()

                if e.args[0] == ERROR_ACCESS_DENIED:

                    raise errors.LockFailed(filename, e)

                if e.args[0] == ERROR_SHARING_VIOLATION:

                    raise errors.LockContention(filename, e)

                raise e

            fd = msvcrt.open_osfhandle(handle, cflags)

            self.f = os.fdopen(fd, pymode)

            return self.f

        def unlock(self):

            self._clear_f()

    class _ctypes_ReadLock(_ctypes_FileLock):

        def __init__(self, filename):

            super(_ctypes_ReadLock, self).__init__()

            self._open(filename, GENERIC_READ, FILE_SHARE_READ, os.O_RDONLY,

                "rb")

        def temporary_write_lock(self):

            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock

            without unlocking the file.

            Otherwise, this will release the read lock, and try to acquire a

            write lock.

            :return: A token which can be used to switch back to a read lock.

            """

            # I can't find a way to upgrade a read lock to a write lock without

            # unlocking first. So here, we do just that.

            self.unlock()

            try:

                wlock = _ctypes_WriteLock(self.filename)

            except errors.LockError:

                return False, _ctypes_ReadLock(self.filename)

            return True, wlock

    class _ctypes_WriteLock(_ctypes_FileLock):

        def __init__(self, filename):

            super(_ctypes_WriteLock, self).__init__()

            self._open(filename, GENERIC_READ | GENERIC_WRITE, 0, os.O_RDWR,

                "rb+")

        def restore_read_lock(self):

            """Restore the original ReadLock."""

            # For win32 we had to completely let go of the original lock, so we

            # just unlock and create a new read lock.

            self.unlock()

            return _ctypes_ReadLock(self.filename)

    _lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock))

if len(_lock_classes) == 0:

    raise NotImplementedError(

        "We must have one of fcntl, pywin32, or ctypes available"

        " to support OS locking."

        )

# We default to using the first available lock class.

_lock_type, WriteLock, ReadLock = _lock_classes[0]

class _RelockDebugMixin(object):

    """Mixin support for -Drelock flag.

    Add this as a base class then call self._note_lock with 'r' or 'w' when

    acquiring a read- or write-lock.  If this object was previously locked (and

    locked the same way), and -Drelock is set, then this will trace.note a

    message about it.

    """

    _prev_lock = None

    def _note_lock(self, lock_type):

        if 'relock' in debug.debug_flags and self._prev_lock == lock_type:

            if lock_type == 'r':

                type_name = 'read'

            else:

                type_name = 'write'

            trace.note(gettext('{0!r} was {1} locked again'), self, type_name)

        self._prev_lock = lock_type

@contextlib.contextmanager

def write_locked(lockable):

    lockable.lock_write()

    try:

        yield lockable

    finally:

        lockable.unlock()