# appendfile.py - special classes to make repo updates atomic

#

# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>

#

# This software may be used and distributed according to the terms

# of the GNU General Public License, incorporated herein by reference.

from demandload import *

# writes to metadata files are ordered.  reads: changelog, manifest,

# normal files.  writes: normal files, manifest, changelog.

# manifest contains pointers to offsets in normal files.  changelog

# contains pointers to offsets in manifest.  if reader reads old

# changelog while manifest or normal files are written, it has no

# pointers into new parts of those files that are maybe not consistent

# yet, so will not read them.

# localrepo.addchangegroup thinks it writes changelog first, then

# manifest, then normal files (this is order they are available, and

# needed for computing linkrev fields), but uses appendfile to hide

# updates from readers.  data not written to manifest or changelog

# until all normal files updated.  write manifest first, then

# changelog.

# with this write ordering, readers cannot see inconsistent view of

# repo during update.

class appendfile(object):

    '''implement enough of file protocol to append to revlog file.

    appended data is written to temp file.  reads and seeks span real

    file and temp file.  readers cannot see appended data until

    writedata called.'''

        self.realfp = fp

        self.offset = fp.tell()

        # real file is not written by anyone else. cache its size so

        # seek and read can be fast.

    def end(self):

        self.tmpfp.flush() # make sure the stat is correct

    def seek(self, offset, whence=0):

        '''virtual file offset spans real file and temp file.'''

        if whence == 0:

            self.offset = offset

        elif whence == 1:

            self.offset += offset

        elif whence == 2:

            self.offset = self.end() + offset

            self.realfp.seek(self.offset)

        else:

    def read(self, count=-1):

        '''only trick here is reads that span real file and temp file.'''

        fp = cStringIO.StringIO()

        old_offset = self.offset

            s = self.realfp.read(count)

            fp.write(s)

            self.offset += len(s)

            if count > 0:

                count -= len(s)

        if count != 0:

            if old_offset != self.offset:

            s = self.tmpfp.read(count)

            fp.write(s)

            self.offset += len(s)

        return fp.getvalue()

    def write(self, s):

        '''append to temp file.'''

        self.tmpfp.seek(0, 2)

        self.tmpfp.write(s)

        # all writes are appends, so offset must go to end of file.

class appendopener(object):

    '''special opener for files that only read or append.'''

    def __init__(self, opener):

        self.realopener = opener

    def __call__(self, name, mode='r'):

        assert mode in 'ra+'

    def writedata(self):

        '''copy data from temp files to real files.'''

        # write .d file before .i file.

# files for changelog and manifest are in different appendopeners, so

# not mixed up together.

class appendchangelog(changelog.changelog, appendopener):

    def __init__(self, opener, version):

        appendopener.__init__(self, opener)

        changelog.changelog.__init__(self, self, version)

    def checkinlinesize(self, fp, tr):

        return

class appendmanifest(manifest.manifest, appendopener):

    def __init__(self, opener, version):

        appendopener.__init__(self, opener)

        manifest.manifest.__init__(self, self, version)

    def checkinlinesize(self, fp, tr):

        return