~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005, 2006, 2008, 2009, 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

import os

from bzrlib.lazy_import import lazy_import

lazy_import(globals(), """

import stat

import warnings

from bzrlib import (

    errors,

    osutils,

    symbol_versioning,

    )

""")

# not forksafe - but we dont fork.

_pid = os.getpid()

_hostname = None

class AtomicFile(object):

    """A file that does an atomic-rename to move into place.

    This also causes hardlinks to break when it's written out.

    Open this as for a regular file, then use commit() to move into

    place or abort() to cancel.

    """

    __slots__ = ['tmpfilename', 'realfilename', '_fd']

    def __init__(self, filename, mode='wb', new_mode=None):

        global _hostname

        self._fd = None

        if _hostname is None:

            _hostname = osutils.get_host_name()

        self.tmpfilename = '%s.%d.%s.%s.tmp' % (filename, _pid, _hostname,

                                                osutils.rand_chars(10))

        self.realfilename = filename

        flags = os.O_EXCL | os.O_CREAT | os.O_WRONLY | osutils.O_NOINHERIT

        if mode == 'wb':

            flags |= osutils.O_BINARY

        elif mode != 'wt':

            raise ValueError("invalid AtomicFile mode %r" % mode)

        if new_mode is not None:

            local_mode = new_mode

        else:

            local_mode = 0666

        # Use a low level fd operation to avoid chmodding later.

        # This may not succeed, but it should help most of the time

        self._fd = os.open(self.tmpfilename, flags, local_mode)

        if new_mode is not None:

            # Because of umask issues, we may need to chmod anyway

            # the common case is that we won't, though.

            st = os.fstat(self._fd)

            if stat.S_IMODE(st.st_mode) != new_mode:

                os.chmod(self.tmpfilename, new_mode)

    def __repr__(self):

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

                           self.realfilename)

    def write(self, data):

        """Write some data to the file. Like file.write()"""

        os.write(self._fd, data)

    def _close_tmpfile(self, func_name):

        """Close the local temp file in preparation for commit or abort"""

        if self._fd is None:

            raise errors.AtomicFileAlreadyClosed(path=self.realfilename,

                                                 function=func_name)

        fd = self._fd

        self._fd = None

        os.close(fd)

    def commit(self):

        """Close the file and move to final name."""

        self._close_tmpfile('commit')

        osutils.rename(self.tmpfilename, self.realfilename)

    def abort(self):

        """Discard temporary file without committing changes."""

        self._close_tmpfile('abort')

        os.remove(self.tmpfilename)

    def close(self):

        """Discard the file unless already committed."""

        if self._fd is not None:

            self.abort()