~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2004, 2005 by 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

from warnings import warn

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.

    An encoding can be specified; otherwise the default is ascii.

    """

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

        if mode != 'wb' and mode != 'wt':

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

        import os, socket

        self.tmpfilename = '%s.%d.%s.tmp' % (filename, os.getpid(),

                                             socket.gethostname())

        self.realfilename = filename

        if encoding:

            import codecs

            self.f = codecs.open(self.tmpfilename, mode, encoding)

        else:

            self.f = open(self.tmpfilename, mode)

        self.write = self.f.write

        self.closed = False

    def __repr__(self):

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

                           self.realfilename)

    def commit(self):

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

        import sys, os

        if self.closed:

            raise Exception('%r is already closed' % self)

        self.closed = True

        self.f.close()

        self.f = None

        if sys.platform == 'win32':

            # windows cannot rename over an existing file

            try:

                os.remove(self.realfilename)

            except OSError, e:

                import errno

                if e.errno != errno.ENOENT:

                    raise

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

    def abort(self):

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

        import os

        if self.closed:

            raise Exception('%r is already closed' % self)

        self.closed = True

        self.f.close()

        self.f = None

        os.remove(self.tmpfilename)

    def close(self):

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

        if not self.closed:

            self.abort()

    def __del__(self):

        if not self.closed:

            warn("%r leaked" % self)