~bzr-pqm/bzr/bzr.dev

# (C) 2005 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

import stat, os, sha, time

from binascii import b2a_qp, a2b_qp

from trace import mutter

from errors import BzrError

"""File stat cache to speed up tree comparisons.

This module basically gives a quick way to find the SHA-1 and related

information of a file in the working directory, without actually

reading and hashing the whole file.

This is done by maintaining a cache indexed by a file fingerprint of

(path, size, mtime, ctime, ino, dev) pointing to the SHA-1.  If the

fingerprint has changed, we assume the file content has not changed

either and the SHA-1 is therefore the same.

If any of the fingerprint fields have changed then the file content

*may* have changed, or it may not have.  We need to reread the file

contents to make sure, but this is not visible to the user or

higher-level code (except as a delay of course).

The mtime and ctime are stored with nanosecond fields, but not all

filesystems give this level of precision.  There is therefore a

possible race: the file might be modified twice within a second

without changing the size or mtime, and a SHA-1 cached from the first

version would be wrong.  We handle this by not recording a cached hash

for any files which were modified in the current second and that

therefore have the chance to change again before the second is up.

The only known hole in this design is if the system clock jumps

backwards crossing invocations of bzr.  Please don't do that; use ntp

to gradually adjust your clock or don't use bzr over the step.

At the moment this is stored in a simple textfile; it might be nice

to use a tdb instead.

The cache is represented as a map from file_id to a tuple of (file_id,

sha1, path, size, mtime, ctime, ino, dev).

"""

FP_SIZE  = 0

FP_MTIME = 1

FP_CTIME = 2

FP_INO   = 3

FP_DEV   = 4

SC_FILE_ID = 0

SC_SHA1    = 1 

def fingerprint(path, abspath):

    try:

        fs = os.lstat(abspath)

    except OSError:

        # might be missing, etc

        return None

    if stat.S_ISDIR(fs.st_mode):

        return None

    return (fs.st_size, fs.st_mtime,

            fs.st_ctime, fs.st_ino, fs.st_dev)

def _write_cache(branch, entry_iter, dangerfiles):

    from atomicfile import AtomicFile

    outf = AtomicFile(branch.controlfilename('stat-cache'), 'wb', 'utf-8')

    try:

        for entry in entry_iter:

            if entry[0] in dangerfiles:

                continue

            outf.write(entry[0] + ' ' + entry[1] + ' ')

            outf.write(b2a_qp(entry[2], True))

            outf.write(' %d %d %d %d %d\n' % entry[3:])

        outf.commit()

    finally:

        if not outf.closed:

            outf.abort()

def load_cache(branch):

    cache = {}

    try:

        cachefile = branch.controlfile('stat-cache', 'r')

    except IOError:

        return cache

    for l in cachefile:

        f = l.split(' ')

        file_id = f[0]

        if file_id in cache:

            raise BzrError("duplicated file_id in cache: {%s}" % file_id)

        cache[file_id] = (f[0], f[1], a2b_qp(f[2])) + tuple([long(x) for x in f[3:]])

    return cache

def _files_from_inventory(inv):

    for path, ie in inv.iter_entries():

        if ie.kind != 'file':

            continue

        yield ie.file_id, path

def update_cache(branch, inv=None, flush=False):

    """Update and return the cache for the branch.

    The returned cache may contain entries that have not been written

    to disk for files recently touched.

    flush -- discard any previous cache and recalculate from scratch.

    """

    # TODO: It's supposed to be faster to stat the files in order by inum.

    # We don't directly know the inum of the files of course but we do

    # know where they were last sighted, so we can sort by that.

    assert isinstance(flush, bool)

    if flush:

        cache = {}

    else:

        cache = load_cache(branch)

    if inv == None:

        inv = branch.read_working_inventory()

    return _update_cache_from_list(branch, cache, _files_from_inventory(inv))

def _update_cache_from_list(branch, cache, to_update):

    """Update and return the cache for given files.

    cache -- Previously cached values to be validated.

    to_update -- Sequence of (file_id, path) pairs to check.

    """

    from sets import Set

    hardcheck = dirty = 0

    # files that have been recently touched and can't be

    # committed to a persistent cache yet.

    dangerfiles = Set()

    now = int(time.time())

    for file_id, path in to_update:

        fap = branch.abspath(path)

        fp = fingerprint(fap, path)

        cacheentry = cache.get(file_id)

        if fp == None: # not here

            if cacheentry:

                del cache[file_id]

                dirty += 1

            continue

        if (fp[FP_MTIME] >= now) or (fp[FP_CTIME] >= now):

            dangerfiles.add(file_id)

        if cacheentry and (cacheentry[3:] == fp):

            continue                    # all stat fields unchanged

        hardcheck += 1

        dig = sha.new(file(fap, 'rb').read()).hexdigest()

        if cacheentry == None or dig != cacheentry[1]: 

            # if there was no previous entry for this file, or if the

            # SHA has changed, then update the cache

            cacheentry = (file_id, dig, path) + fp

            cache[file_id] = cacheentry

            dirty += 1

    mutter('statcache: read %d files, %d changed, %d dangerous, '

           '%d in cache'

           % (hardcheck, dirty, len(dangerfiles), len(cache)))

    if dirty:

        mutter('updating on-disk statcache')

        _write_cache(branch, cache.itervalues(), dangerfiles)

    return cache