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- Committer: Martin Pool
- Date: 2005-05-13 00:57:32 UTC
- Revision ID: mbp@sourcefrog.net-20050513005732-26b0a3042cbb57d1
- more notes on tagging
- files added:
- bzrlib/atomicfile.py
- files removed:
- doc/faq.txt
- files modified:
- .bzrignore
added
removed
bzrlib/statcache.py
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# (C) 2005 Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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import stat, os, sha, time
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from binascii import b2a_qp, a2b_qp
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from trace import mutter
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from errors import BzrError
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"""File stat cache to speed up tree comparisons.
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This module basically gives a quick way to find the SHA-1 and related
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information of a file in the working directory, without actually
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reading and hashing the whole file.
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This is done by maintaining a cache indexed by a file fingerprint of
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(path, size, mtime, ctime, ino, dev) pointing to the SHA-1. If the
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fingerprint has changed, we assume the file content has not changed
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either and the SHA-1 is therefore the same.
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If any of the fingerprint fields have changed then the file content
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*may* have changed, or it may not have. We need to reread the file
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contents to make sure, but this is not visible to the user or
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higher-level code (except as a delay of course).
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The mtime and ctime are stored with nanosecond fields, but not all
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filesystems give this level of precision. There is therefore a
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possible race: the file might be modified twice within a second
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without changing the size or mtime, and a SHA-1 cached from the first
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version would be wrong. We handle this by not recording a cached hash
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for any files which were modified in the current second and that
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therefore have the chance to change again before the second is up.
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The only known hole in this design is if the system clock jumps
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backwards crossing invocations of bzr. Please don't do that; use ntp
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to gradually adjust your clock or don't use bzr over the step.
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At the moment this is stored in a simple textfile; it might be nice
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to use a tdb instead.
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The cache is represented as a map from file_id to a tuple of (file_id,
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sha1, path, size, mtime, ctime, ino, dev).
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"""
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FP_SIZE = 0
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FP_MTIME = 1
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FP_CTIME = 2
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FP_INO = 3
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FP_DEV = 4
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SC_FILE_ID = 0
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SC_SHA1 = 1
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def fingerprint(abspath):
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try:
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fs = os.lstat(abspath)
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except OSError:
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# might be missing, etc
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return None
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if stat.S_ISDIR(fs.st_mode):
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return None
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return (fs.st_size, fs.st_mtime,
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fs.st_ctime, fs.st_ino, fs.st_dev)
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def _write_cache(basedir, entry_iter, dangerfiles):
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from atomicfile import AtomicFile
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cachefn = os.path.join(basedir, '.bzr', 'stat-cache')
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outf = AtomicFile(cachefn, 'wb', 'utf-8')
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try:
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for entry in entry_iter:
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if entry[0] in dangerfiles:
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continue
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outf.write(entry[0] + ' ' + entry[1] + ' ')
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outf.write(b2a_qp(entry[2], True))
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outf.write(' %d %d %d %d %d\n' % entry[3:])
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outf.commit()
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finally:
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if not outf.closed:
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outf.abort()
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def load_cache(basedir):
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import codecs
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cache = {}
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try:
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cachefn = os.path.join(basedir, '.bzr', 'stat-cache')
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cachefile = codecs.open(cachefn, 'r', 'utf-8')
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except IOError:
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return cache
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for l in cachefile:
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f = l.split(' ')
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file_id = f[0]
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if file_id in cache:
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raise BzrError("duplicated file_id in cache: {%s}" % file_id)
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cache[file_id] = (f[0], f[1], a2b_qp(f[2])) + tuple([long(x) for x in f[3:]])
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return cache
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def _files_from_inventory(inv):
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for path, ie in inv.iter_entries():
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if ie.kind != 'file':
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continue
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yield ie.file_id, path
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def update_cache(basedir, inv, flush=False):
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"""Update and return the cache for the branch.
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The returned cache may contain entries that have not been written
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to disk for files recently touched.
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flush -- discard any previous cache and recalculate from scratch.
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"""
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# TODO: It's supposed to be faster to stat the files in order by inum.
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# We don't directly know the inum of the files of course but we do
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# know where they were last sighted, so we can sort by that.
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assert isinstance(flush, bool)
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if flush:
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cache = {}
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else:
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cache = load_cache(basedir)
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return _update_cache_from_list(basedir, cache, _files_from_inventory(inv))
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def _update_cache_from_list(basedir, cache, to_update):
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"""Update and return the cache for given files.
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cache -- Previously cached values to be validated.
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to_update -- Sequence of (file_id, path) pairs to check.
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"""
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from sets import Set
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stat_cnt = missing_cnt = hardcheck = change_cnt = 0
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# files that have been recently touched and can't be
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# committed to a persistent cache yet.
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dangerfiles = Set()
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now = int(time.time())
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## mutter('update statcache under %r' % basedir)
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for file_id, path in to_update:
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abspath = os.path.join(basedir, path)
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fp = fingerprint(abspath)
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stat_cnt += 1
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cacheentry = cache.get(file_id)
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if fp == None: # not here
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if cacheentry:
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del cache[file_id]
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change_cnt += 1
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missing_cnt += 1
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continue
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if (fp[FP_MTIME] >= now) or (fp[FP_CTIME] >= now):
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dangerfiles.add(file_id)
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if cacheentry and (cacheentry[3:] == fp):
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continue # all stat fields unchanged
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hardcheck += 1
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dig = sha.new(file(abspath, 'rb').read()).hexdigest()
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# We update the cache even if the digest has not changed from
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# last time we looked, so that the fingerprint fields will
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# match in future.
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cacheentry = (file_id, dig, path) + fp
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cache[file_id] = cacheentry
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change_cnt += 1
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mutter('statcache: statted %d files, read %d files, %d changed, %d dangerous, '
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'%d in cache'
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% (stat_cnt, hardcheck, change_cnt, len(dangerfiles), len(cache)))
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if change_cnt:
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mutter('updating on-disk statcache')
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_write_cache(basedir, cache.itervalues(), dangerfiles)
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return cache
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