1
# (C) 2005 Canonical Ltd
3
# This program is free software; you can redistribute it and/or modify
4
# it under the terms of the GNU General Public License as published by
5
# the Free Software Foundation; either version 2 of the License, or
6
# (at your option) any later version.
8
# This program is distributed in the hope that it will be useful,
9
# but WITHOUT ANY WARRANTY; without even the implied warranty of
10
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11
# GNU General Public License for more details.
13
# You should have received a copy of the GNU General Public License
14
# along with this program; if not, write to the Free Software
15
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
17
import stat, os, sha, time
18
from binascii import b2a_qp, a2b_qp
20
from trace import mutter
21
from errors import BzrError
24
"""File stat cache to speed up tree comparisons.
26
This module basically gives a quick way to find the SHA-1 and related
27
information of a file in the working directory, without actually
28
reading and hashing the whole file.
30
This is done by maintaining a cache indexed by a file fingerprint of
31
(path, size, mtime, ctime, ino, dev) pointing to the SHA-1. If the
32
fingerprint has changed, we assume the file content has not changed
33
either and the SHA-1 is therefore the same.
35
If any of the fingerprint fields have changed then the file content
36
*may* have changed, or it may not have. We need to reread the file
37
contents to make sure, but this is not visible to the user or
38
higher-level code (except as a delay of course).
40
The mtime and ctime are stored with nanosecond fields, but not all
41
filesystems give this level of precision. There is therefore a
42
possible race: the file might be modified twice within a second
43
without changing the size or mtime, and a SHA-1 cached from the first
44
version would be wrong. We handle this by not recording a cached hash
45
for any files which were modified in the current second and that
46
therefore have the chance to change again before the second is up.
48
The only known hole in this design is if the system clock jumps
49
backwards crossing invocations of bzr. Please don't do that; use ntp
50
to gradually adjust your clock or don't use bzr over the step.
52
At the moment this is stored in a simple textfile; it might be nice
58
def fingerprint(path, abspath):
60
fs = os.lstat(abspath)
62
# might be missing, etc
65
if stat.S_ISDIR(fs.st_mode):
68
return (fs.st_size, fs.st_mtime,
69
fs.st_ctime, fs.st_ino, fs.st_dev)
72
def write_cache(branch, entry_iter):
73
from atomicfile import AtomicFile
75
outf = AtomicFile(branch.controlfilename('work-cache.tmp'), 'wt')
77
for entry in entry_iter:
78
outf.write(entry[0] + ' ' + entry[1] + ' ')
79
outf.write(b2a_qp(entry[2], True))
80
outf.write(' %d %d %d %d %d\n' % entry[3:])
88
def load_cache(branch):
92
cachefile = branch.controlfile('work-cache', 'rt')
100
raise BzrError("duplicated file_id in cache: {%s}" % file_id)
101
cache[file_id] = (f[0], f[1], a2b_qp(f[2])) + tuple([long(x) for x in f[3:]])
107
def _files_from_inventory(inv):
108
for path, ie in inv.iter_entries():
109
if ie.kind != 'file':
111
yield ie.file_id, path
114
def build_cache(branch):
115
inv = branch.read_working_inventory()
118
_update_cache_from_list(branch, cache, _files_from_inventory(inv))
122
def update_cache(branch, inv):
123
# TODO: It's supposed to be faster to stat the files in order by inum.
124
# We don't directly know the inum of the files of course but we do
125
# know where they were last sighted, so we can sort by that.
127
cache = load_cache(branch)
128
return _update_cache_from_list(branch, cache, _files_from_inventory(inv))
132
def _update_cache_from_list(branch, cache, to_update):
133
"""Update the cache to have info on the named files.
135
to_update is a sequence of (file_id, path) pairs.
137
hardcheck = dirty = 0
138
for file_id, path in to_update:
139
fap = branch.abspath(path)
140
fp = fingerprint(fap, path)
141
cacheentry = cache.get(file_id)
143
if fp == None: # not here
149
if cacheentry and (cacheentry[3:] == fp):
150
continue # all stat fields unchanged
154
dig = sha.new(file(fap, 'rb').read()).hexdigest()
156
if cacheentry == None or dig != cacheentry[1]:
157
# if there was no previous entry for this file, or if the
158
# SHA has changed, then update the cache
159
cacheentry = (file_id, dig, path) + fp
160
cache[file_id] = cacheentry
163
mutter('work cache: read %d files, %d changed' % (hardcheck, dirty))
166
write_cache(branch, cache.itervalues())
added
removed
bzrlib/cache.py
