~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005, 2006, 2007 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


"""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.
"""

import errno
import sys

from bzrlib import (
    errors,
    osutils,
    trace,
    )


class _base_Lock(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.ReadOnlyLockError(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 __del__(self):
        if self.f:
            from warnings import warn
            warn("lock on %r not released" % self.f)
            self.unlock()

    def unlock(self):
        raise NotImplementedError()


try:
    import fcntl
    have_fcntl = True
except ImportError:
    have_fcntl = False
try:
    import win32con, win32file, pywintypes, winerror, msvcrt
    have_pywin32 = True
except ImportError:
    have_pywin32 = False
try:
    import ctypes, msvcrt
    have_ctypes = True
except ImportError:
    have_ctypes = False


_lock_classes = []


if have_fcntl:
    LOCK_SH = fcntl.LOCK_SH
    LOCK_NB = fcntl.LOCK_NB
    lock_EX = fcntl.LOCK_EX


    class _fcntl_FileLock(_base_Lock):

        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)

            self._open(self.filename, 'rb+')
            # reserve a slot for this lock - even if the lockf call fails,
            # at thisi 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(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)
            _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(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.
            """
            assert self.filename not in _fcntl_WriteLock._open_locks
            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(_base_Lock):
        """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)

            assert self.filename not in _fcntl_WriteLock._open_locks

            # 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.ReadOnlyLockError(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(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':
    LOCK_SH = 0 # the default
    LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
    LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY


    class _w32c_FileLock(_base_Lock):

        def _lock(self, filename, openmode, lockmode):
            self._open(filename, openmode)

            self.hfile = msvcrt.get_osfhandle(self.f.fileno())
            overlapped = pywintypes.OVERLAPPED()
            try:
                win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000,
                                     overlapped)
            except pywintypes.error, e:
                self._clear_f()
                if e.args[0] in (winerror.ERROR_LOCK_VIOLATION,):
                    raise errors.LockContention(filename)
                ## import pdb; pdb.set_trace()
                raise
            except Exception, e:
                self._clear_f()
                raise errors.LockContention(e)

        def unlock(self):
            overlapped = pywintypes.OVERLAPPED()
            try:
                win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
                self._clear_f()
            except Exception, e:
                raise errors.LockContention(e)


    class _w32c_ReadLock(_w32c_FileLock):
        def __init__(self, filename):
            super(_w32c_ReadLock, self).__init__()
            self._lock(filename, 'rb', LOCK_SH + LOCK_NB)

        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._lock(filename, 'rb+', LOCK_EX + LOCK_NB)

        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 and sys.platform == 'win32':
    # These constants were copied from the win32con.py module.
    LOCKFILE_FAIL_IMMEDIATELY = 1
    LOCKFILE_EXCLUSIVE_LOCK = 2
    # Constant taken from winerror.py module
    ERROR_LOCK_VIOLATION = 33

    LOCK_SH = 0
    LOCK_EX = LOCKFILE_EXCLUSIVE_LOCK
    LOCK_NB = LOCKFILE_FAIL_IMMEDIATELY
    _LockFileEx = ctypes.windll.kernel32.LockFileEx
    _UnlockFileEx = ctypes.windll.kernel32.UnlockFileEx
    _GetLastError = ctypes.windll.kernel32.GetLastError

    ### Define the OVERLAPPED structure.
    #   http://msdn2.microsoft.com/en-us/library/ms684342.aspx
    # typedef struct _OVERLAPPED {
    #   ULONG_PTR Internal;
    #   ULONG_PTR InternalHigh;
    #   union {
    #     struct {
    #       DWORD Offset;
    #       DWORD OffsetHigh;
    #     };
    #     PVOID Pointer;
    #   };
    #   HANDLE hEvent;
    # } OVERLAPPED,

    class _inner_struct(ctypes.Structure):
        _fields_ = [('Offset', ctypes.c_uint), # DWORD
                    ('OffsetHigh', ctypes.c_uint), # DWORD
                   ]

    class _inner_union(ctypes.Union):
        _fields_  = [('anon_struct', _inner_struct), # struct
                     ('Pointer', ctypes.c_void_p), # PVOID
                    ]

    class OVERLAPPED(ctypes.Structure):
        _fields_ = [('Internal', ctypes.c_void_p), # ULONG_PTR
                    ('InternalHigh', ctypes.c_void_p), # ULONG_PTR
                    ('_inner_union', _inner_union),
                    ('hEvent', ctypes.c_void_p), # HANDLE
                   ]

    class _ctypes_FileLock(_base_Lock):

        def _lock(self, filename, openmode, lockmode):
            self._open(filename, openmode)

            self.hfile = msvcrt.get_osfhandle(self.f.fileno())
            overlapped = OVERLAPPED()
            result = _LockFileEx(self.hfile, # HANDLE hFile
                                 lockmode,   # DWORD dwFlags
                                 0,          # DWORD dwReserved
                                 0x7fffffff, # DWORD nNumberOfBytesToLockLow
                                 0x00000000, # DWORD nNumberOfBytesToLockHigh
                                 ctypes.byref(overlapped), # lpOverlapped
                                )
            if result == 0:
                self._clear_f()
                last_err = _GetLastError()
                if last_err in (ERROR_LOCK_VIOLATION,):
                    raise errors.LockContention(filename)
                raise errors.LockContention('Unknown locking error: %s'
                                            % (last_err,))

        def unlock(self):
            overlapped = OVERLAPPED()
            result = _UnlockFileEx(self.hfile, # HANDLE hFile
                                   0,          # DWORD dwReserved
                                   0x7fffffff, # DWORD nNumberOfBytesToLockLow
                                   0x00000000, # DWORD nNumberOfBytesToLockHigh
                                   ctypes.byref(overlapped), # lpOverlapped
                                  )
            self._clear_f()
            if result == 0:
                self._clear_f()
                last_err = _GetLastError()
                raise errors.LockContention('Unknown unlocking error: %s'
                                            % (last_err,))


    class _ctypes_ReadLock(_ctypes_FileLock):
        def __init__(self, filename):
            super(_ctypes_ReadLock, self).__init__()
            self._lock(filename, 'rb', LOCK_SH + LOCK_NB)

        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._lock(filename, 'rb+', LOCK_EX + LOCK_NB)

        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]