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# Copyright (C) 2005, 2006 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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# TODO: Up-front, stat all files in order and remove those which are deleted or
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# out-of-date. Don't actually re-read them until they're needed. That ought
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# to bring all the inodes into core so that future stats to them are fast, and
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# it preserves the nice property that any caller will always get up-to-date
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# data except in unavoidable cases.
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# TODO: Perhaps return more details on the file to avoid statting it
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# again: nonexistent, file type, size, etc
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# TODO: Perhaps use a Python pickle instead of a text file; might be faster.
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CACHE_HEADER = "### bzr hashcache v5\n"
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from bzrlib.osutils import sha_file, sha_string, pathjoin, safe_unicode
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from bzrlib.trace import mutter, warning
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from bzrlib.atomicfile import AtomicFile
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from bzrlib.errors import BzrError
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class HashCache(object):
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"""Cache for looking up file SHA-1.
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Files are considered to match the cached value if the fingerprint
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of the file has not changed. This includes its mtime, ctime,
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device number, inode number, and size. This should catch
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modifications or replacement of the file by a new one.
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This may not catch modifications that do not change the file's
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size and that occur within the resolution window of the
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timestamps. To handle this we specifically do not cache files
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which have changed since the start of the present second, since
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they could undetectably change again.
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This scheme may fail if the machine's clock steps backwards.
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This does not canonicalize the paths passed in; that should be
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Indexed by path, points to a two-tuple of the SHA-1 of the file.
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number of times files have been statted
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number of times files have been retrieved from the cache, avoiding a
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number of misses (times files have been completely re-read)
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def __init__(self, root, cache_file_name, mode=None):
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"""Create a hash cache in base dir, and set the file mode to mode."""
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self.root = safe_unicode(root)
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self.root_utf8 = self.root.encode('utf8') # where is the filesystem encoding ?
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self.removed_count = 0
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self._cache_file_name = safe_unicode(cache_file_name)
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def cache_file_name(self):
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return self._cache_file_name
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"""Discard all cached information.
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This does not reset the counters."""
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self.needs_write = True
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"""Scan all files and remove entries where the cache entry is obsolete.
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Obsolete entries are those where the file has been modified or deleted
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since the entry was inserted.
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# FIXME optimisation opportunity, on linux [and check other oses]:
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# rather than iteritems order, stat in inode order.
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prep = [(ce[1][3], path, ce) for (path, ce) in self._cache.iteritems()]
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for inum, path, cache_entry in prep:
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abspath = pathjoin(self.root, path)
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fp = self._fingerprint(abspath)
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cache_fp = cache_entry[1]
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if (not fp) or (cache_fp != fp):
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# not here or not a regular file anymore
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self.removed_count += 1
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self.needs_write = True
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del self._cache[path]
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def get_sha1(self, path, stat_value=None):
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"""Return the sha1 of a file.
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if path.__class__ is str:
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abspath = pathjoin(self.root_utf8, path)
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abspath = pathjoin(self.root, path)
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file_fp = self._fingerprint(abspath, stat_value)
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# not a regular file or not existing
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if path in self._cache:
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self.removed_count += 1
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self.needs_write = True
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del self._cache[path]
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if path in self._cache:
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cache_sha1, cache_fp = self._cache[path]
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cache_sha1, cache_fp = None, None
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if cache_fp == file_fp:
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## mutter("hashcache hit for %s %r -> %s", path, file_fp, cache_sha1)
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## mutter("now = %s", time.time())
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mode = file_fp[FP_MODE_COLUMN]
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if stat.S_ISREG(mode):
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digest = self._really_sha1_file(abspath)
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elif stat.S_ISLNK(mode):
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digest = sha_string(os.readlink(abspath))
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raise BzrError("file %r: unknown file stat mode: %o"%(abspath,mode))
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# window of 3 seconds to allow for 2s resolution on windows,
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# unsynchronized file servers, etc.
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cutoff = self._cutoff_time()
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if file_fp[FP_MTIME_COLUMN] >= cutoff \
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or file_fp[FP_CTIME_COLUMN] >= cutoff:
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# changed too recently; can't be cached. we can
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# return the result and it could possibly be cached
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# the point is that we only want to cache when we are sure that any
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# subsequent modifications of the file can be detected. If a
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# modification neither changes the inode, the device, the size, nor
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# the mode, then we can only distinguish it by time; therefore we
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# need to let sufficient time elapse before we may cache this entry
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# again. If we didn't do this, then, for example, a very quick 1
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# byte replacement in the file might go undetected.
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## mutter('%r modified too recently; not caching', path)
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self.danger_count += 1
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self.removed_count += 1
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self.needs_write = True
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del self._cache[path]
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## mutter('%r added to cache: now=%f, mtime=%d, ctime=%d',
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## path, time.time(), file_fp[FP_MTIME_COLUMN],
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## file_fp[FP_CTIME_COLUMN])
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self.update_count += 1
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self.needs_write = True
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self._cache[path] = (digest, file_fp)
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def _really_sha1_file(self, abspath):
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"""Calculate the SHA1 of a file by reading the full text"""
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return sha_file(file(abspath, 'rb', buffering=65000))
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"""Write contents of cache to file."""
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outf = AtomicFile(self.cache_file_name(), 'wb', new_mode=self._mode)
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outf.write(CACHE_HEADER)
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for path, c in self._cache.iteritems():
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line_info = [path.encode('utf-8'), '// ', c[0], ' ']
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line_info.append(' '.join([str(fld) for fld in c[1]]))
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line_info.append('\n')
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outf.write(''.join(line_info))
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self.needs_write = False
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## mutter("write hash cache: %s hits=%d misses=%d stat=%d recent=%d updates=%d",
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## self.cache_file_name(), self.hit_count, self.miss_count,
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## self.danger_count, self.update_count)
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"""Reinstate cache from file.
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Overwrites existing cache.
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If the cache file has the wrong version marker, this just clears
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fn = self.cache_file_name()
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inf = file(fn, 'rb', buffering=65000)
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mutter("failed to open %s: %s", fn, e)
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# better write it now so it is valid
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self.needs_write = True
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if hdr != CACHE_HEADER:
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mutter('cache header marker not found at top of %s;'
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' discarding cache', fn)
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self.needs_write = True
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path = l[:pos].decode('utf-8')
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if path in self._cache:
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warning('duplicated path %r in cache' % path)
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fields = l[pos:].split(' ')
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warning("bad line in hashcache: %r" % l)
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warning("bad sha1 in hashcache: %r" % sha1)
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fp = tuple(map(long, fields[1:]))
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self._cache[path] = (sha1, fp)
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self.needs_write = False
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def _cutoff_time(self):
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"""Return cutoff time.
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Files modified more recently than this time are at risk of being
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undetectably modified and so can't be cached.
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return int(time.time()) - 3
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def _fingerprint(self, abspath, stat_value=None):
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if stat_value is None:
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stat_value = os.lstat(abspath)
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# might be missing, etc
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if stat.S_ISDIR(stat_value.st_mode):
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# we discard any high precision because it's not reliable; perhaps we
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# could do better on some systems?
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return (stat_value.st_size, long(stat_value.st_mtime),
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long(stat_value.st_ctime), stat_value.st_ino,
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stat_value.st_dev, stat_value.st_mode)
added
removed
bzrlib/hashcache.py
