fncachestore: copy dh directory before the manifest

Before this patch, the copy order on clone was:

  requires
  00changelog.i
  store\data
  store\00manifest.d
  store\00manifest.i
  store\00changelog.d
  store\00changelog.i
  store\dh
  store\fncache

Which provides a theoretical non-zero probability of a race during clone where
a very early reader might see a repository with missing revlog files if it sees
00changelog.i before all files inside dh have been copied.

The dh directory is similar to the data directory -- just for files with long
names (which are hashed). The manifest refers to files in data *and* dh, so dh
should be copied before the manifest.

This patch improves the copy order to:

  requires
  00changelog.i
  store\data
  store\dh
  store\fncache
  store\00manifest.d
  store\00manifest.i
  store\00changelog.d
  store\00changelog.i

I'm putting fncache to before the manifest while I'm at it, since fncache
provides a mechanism to enumerate all repository files without visiting the
manifest revisions. fncache depends only on data and dh.

Note that data must be copied first, since copying data triggers the creation
of the repository write lock in the destination repo (see hg.clone).

mercurial/store.py

@@ -1,338 +1,339 b''
 # store.py - repository store handling for Mercurial
 #
 # Copyright 2008 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
 import osutil, util
 import os, stat
 
 _sha = util.sha1
 
 # This avoids a collision between a file named foo and a dir named
 # foo.i or foo.d
 def encodedir(path):
     if not path.startswith('data/'):
         return path
     return (path
             .replace(".hg/", ".hg.hg/")
             .replace(".i/", ".i.hg/")
             .replace(".d/", ".d.hg/"))
 
 def decodedir(path):
     if not path.startswith('data/') or ".hg/" not in path:
         return path
     return (path
             .replace(".d.hg/", ".d/")
             .replace(".i.hg/", ".i/")
             .replace(".hg.hg/", ".hg/"))
 
 def _buildencodefun():
     e = '_'
     win_reserved = [ord(x) for x in '\\:*?"<>|']
     cmap = dict([(chr(x), chr(x)) for x in xrange(127)])
     for x in (range(32) + range(126, 256) + win_reserved):
         cmap[chr(x)] = "~%02x" % x
     for x in range(ord("A"), ord("Z")+1) + [ord(e)]:
         cmap[chr(x)] = e + chr(x).lower()
     dmap = {}
     for k, v in cmap.iteritems():
         dmap[v] = k
     def decode(s):
         i = 0
         while i < len(s):
             for l in xrange(1, 4):
                 try:
                     yield dmap[s[i:i + l]]
                     i += l
                     break
                 except KeyError:
                     pass
             else:
                 raise KeyError
     return (lambda s: "".join([cmap[c] for c in encodedir(s)]),
             lambda s: decodedir("".join(list(decode(s)))))
 
 encodefilename, decodefilename = _buildencodefun()
 
 def _build_lower_encodefun():
     win_reserved = [ord(x) for x in '\\:*?"<>|']
     cmap = dict([(chr(x), chr(x)) for x in xrange(127)])
     for x in (range(32) + range(126, 256) + win_reserved):
         cmap[chr(x)] = "~%02x" % x
     for x in range(ord("A"), ord("Z")+1):
         cmap[chr(x)] = chr(x).lower()
     return lambda s: "".join([cmap[c] for c in s])
 
 lowerencode = _build_lower_encodefun()
 
 _windows_reserved_filenames = '''con prn aux nul
     com1 com2 com3 com4 com5 com6 com7 com8 com9
     lpt1 lpt2 lpt3 lpt4 lpt5 lpt6 lpt7 lpt8 lpt9'''.split()
 def _auxencode(path, dotencode):
     res = []
     for n in path.split('/'):
         if n:
             base = n.split('.')[0]
             if base and (base in _windows_reserved_filenames):
                 # encode third letter ('aux' -> 'au~78')
                 ec = "~%02x" % ord(n[2])
                 n = n[0:2] + ec + n[3:]
             if n[-1] in '. ':
                 # encode last period or space ('foo...' -> 'foo..~2e')
                 n = n[:-1] + "~%02x" % ord(n[-1])
             if dotencode and n[0] in '. ':
                 n = "~%02x" % ord(n[0]) + n[1:]
         res.append(n)
     return '/'.join(res)
 
 MAX_PATH_LEN_IN_HGSTORE = 120
 DIR_PREFIX_LEN = 8
 _MAX_SHORTENED_DIRS_LEN = 8 * (DIR_PREFIX_LEN + 1) - 4
 def _hybridencode(path, auxencode):
     '''encodes path with a length limit
 
     Encodes all paths that begin with 'data/', according to the following.
 
     Default encoding (reversible):
 
     Encodes all uppercase letters 'X' as '_x'. All reserved or illegal
     characters are encoded as '~xx', where xx is the two digit hex code
     of the character (see encodefilename).
     Relevant path components consisting of Windows reserved filenames are
     masked by encoding the third character ('aux' -> 'au~78', see auxencode).
 
     Hashed encoding (not reversible):
 
     If the default-encoded path is longer than MAX_PATH_LEN_IN_HGSTORE, a
     non-reversible hybrid hashing of the path is done instead.
     This encoding uses up to DIR_PREFIX_LEN characters of all directory
     levels of the lowerencoded path, but not more levels than can fit into
     _MAX_SHORTENED_DIRS_LEN.
     Then follows the filler followed by the sha digest of the full path.
     The filler is the beginning of the basename of the lowerencoded path
     (the basename is everything after the last path separator). The filler
     is as long as possible, filling in characters from the basename until
     the encoded path has MAX_PATH_LEN_IN_HGSTORE characters (or all chars
     of the basename have been taken).
     The extension (e.g. '.i' or '.d') is preserved.
 
     The string 'data/' at the beginning is replaced with 'dh/', if the hashed
     encoding was used.
     '''
     if not path.startswith('data/'):
         return path
     # escape directories ending with .i and .d
     path = encodedir(path)
     ndpath = path[len('data/'):]
     res = 'data/' + auxencode(encodefilename(ndpath))
     if len(res) > MAX_PATH_LEN_IN_HGSTORE:
         digest = _sha(path).hexdigest()
         aep = auxencode(lowerencode(ndpath))
         _root, ext = os.path.splitext(aep)
         parts = aep.split('/')
         basename = parts[-1]
         sdirs = []
         for p in parts[:-1]:
             d = p[:DIR_PREFIX_LEN]
             if d[-1] in '. ':
                 # Windows can't access dirs ending in period or space
                 d = d[:-1] + '_'
             t = '/'.join(sdirs) + '/' + d
             if len(t) > _MAX_SHORTENED_DIRS_LEN:
                 break
             sdirs.append(d)
         dirs = '/'.join(sdirs)
         if len(dirs) > 0:
             dirs += '/'
         res = 'dh/' + dirs + digest + ext
         space_left = MAX_PATH_LEN_IN_HGSTORE - len(res)
         if space_left > 0:
             filler = basename[:space_left]
             res = 'dh/' + dirs + filler + digest + ext
     return res
 
 def _calcmode(path):
     try:
         # files in .hg/ will be created using this mode
         mode = os.stat(path).st_mode
             # avoid some useless chmods
         if (0777 & ~util.umask) == (0777 & mode):
             mode = None
     except OSError:
         mode = None
     return mode
 
 _data = 'data 00manifest.d 00manifest.i 00changelog.d 00changelog.i'
 
 class basicstore(object):
     '''base class for local repository stores'''
     def __init__(self, path, opener, pathjoiner):
         self.pathjoiner = pathjoiner
         self.path = path
         self.createmode = _calcmode(path)
         op = opener(self.path)
         op.createmode = self.createmode
         self.opener = lambda f, *args, **kw: op(encodedir(f), *args, **kw)
 
     def join(self, f):
         return self.pathjoiner(self.path, encodedir(f))
 
     def _walk(self, relpath, recurse):
         '''yields (unencoded, encoded, size)'''
         path = self.pathjoiner(self.path, relpath)
         striplen = len(self.path) + len(os.sep)
         l = []
         if os.path.isdir(path):
             visit = [path]
             while visit:
                 p = visit.pop()
                 for f, kind, st in osutil.listdir(p, stat=True):
                     fp = self.pathjoiner(p, f)
                     if kind == stat.S_IFREG and f[-2:] in ('.d', '.i'):
                         n = util.pconvert(fp[striplen:])
                         l.append((decodedir(n), n, st.st_size))
                     elif kind == stat.S_IFDIR and recurse:
                         visit.append(fp)
         return sorted(l)
 
     def datafiles(self):
         return self._walk('data', True)
 
     def walk(self):
         '''yields (unencoded, encoded, size)'''
         # yield data files first
         for x in self.datafiles():
             yield x
         # yield manifest before changelog
         for x in reversed(self._walk('', False)):
             yield x
 
     def copylist(self):
         return ['requires'] + _data.split()
 
 class encodedstore(basicstore):
     def __init__(self, path, opener, pathjoiner):
         self.pathjoiner = pathjoiner
         self.path = self.pathjoiner(path, 'store')
         self.createmode = _calcmode(self.path)
         op = opener(self.path)
         op.createmode = self.createmode
         self.opener = lambda f, *args, **kw: op(encodefilename(f), *args, **kw)
 
     def datafiles(self):
         for a, b, size in self._walk('data', True):
             try:
                 a = decodefilename(a)
             except KeyError:
                 a = None
             yield a, b, size
 
     def join(self, f):
         return self.pathjoiner(self.path, encodefilename(f))
 
     def copylist(self):
         return (['requires', '00changelog.i'] +
                 [self.pathjoiner('store', f) for f in _data.split()])
 
 class fncache(object):
     # the filename used to be partially encoded
     # hence the encodedir/decodedir dance
     def __init__(self, opener):
         self.opener = opener
         self.entries = None
 
     def _load(self):
         '''fill the entries from the fncache file'''
         self.entries = set()
         try:
             fp = self.opener('fncache', mode='rb')
         except IOError:
             # skip nonexistent file
             return
         for n, line in enumerate(fp):
             if (len(line) < 2) or (line[-1] != '\n'):
                 t = _('invalid entry in fncache, line %s') % (n + 1)
                 raise util.Abort(t)
             self.entries.add(decodedir(line[:-1]))
         fp.close()
 
     def rewrite(self, files):
         fp = self.opener('fncache', mode='wb')
         for p in files:
             fp.write(encodedir(p) + '\n')
         fp.close()
         self.entries = set(files)
 
     def add(self, fn):
         if self.entries is None:
             self._load()
         if fn not in self.entries:
             self.opener('fncache', 'ab').write(encodedir(fn) + '\n')
             self.entries.add(fn)
 
     def __contains__(self, fn):
         if self.entries is None:
             self._load()
         return fn in self.entries
 
     def __iter__(self):
         if self.entries is None:
             self._load()
         return iter(self.entries)
 
 class fncachestore(basicstore):
     def __init__(self, path, opener, pathjoiner, encode):
         self.encode = encode
         self.pathjoiner = pathjoiner
         self.path = self.pathjoiner(path, 'store')
         self.createmode = _calcmode(self.path)
         op = opener(self.path)
         op.createmode = self.createmode
         fnc = fncache(op)
         self.fncache = fnc
 
         def fncacheopener(path, mode='r', *args, **kw):
             if mode not in ('r', 'rb') and path.startswith('data/'):
                 fnc.add(path)
             return op(self.encode(path), mode, *args, **kw)
         self.opener = fncacheopener
 
     def join(self, f):
         return self.pathjoiner(self.path, self.encode(f))
 
     def datafiles(self):
         rewrite = False
         existing = []
         pjoin = self.pathjoiner
         spath = self.path
         for f in self.fncache:
             ef = self.encode(f)
             try:
                 st = os.stat(pjoin(spath, ef))
                 yield f, ef, st.st_size
                 existing.append(f)
             except OSError:
                 # nonexistent entry
                 rewrite = True
         if rewrite:
             # rewrite fncache to remove nonexistent entries
             # (may be caused by rollback / strip)
             self.fncache.rewrite(existing)
 
     def copylist(self):
-        d = _data + ' dh fncache'
+        d = ('data dh fncache'
+             ' 00manifest.d 00manifest.i 00changelog.d 00changelog.i')
         return (['requires', '00changelog.i'] +
                 [self.pathjoiner('store', f) for f in d.split()])
 
 def store(requirements, path, opener, pathjoiner=None):
     pathjoiner = pathjoiner or os.path.join
     if 'store' in requirements:
         if 'fncache' in requirements:
             auxencode = lambda f: _auxencode(f, 'dotencode' in requirements)
             encode = lambda f: _hybridencode(f, auxencode)
             return fncachestore(path, opener, pathjoiner, encode)
         return encodedstore(path, opener, pathjoiner)
     return basicstore(path, opener, pathjoiner)