manifest: use a size 3 LRU cache to store parsed manifests

Previously, the manifest cache would store the last manifest parsed. We could
run into situations with operations like update where we would try parsing the
manifest for a revision r1, then r2, then r1 again. This increases the cache
size to 3 to avoid that bit of performance fragility.

mercurial/manifest.py

@@ -1,213 +1,215 b''
 # manifest.py - manifest revision class for mercurial
 #
 # Copyright 2005-2007 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 mdiff, parsers, error, revlog, util
 import array, struct
 
 class manifestdict(dict):
     def __init__(self, mapping=None, flags=None):
         if mapping is None:
             mapping = {}
         if flags is None:
             flags = {}
         dict.__init__(self, mapping)
         self._flags = flags
     def flags(self, f):
         return self._flags.get(f, "")
     def withflags(self):
         return set(self._flags.keys())
     def set(self, f, flags):
         self._flags[f] = flags
     def copy(self):
         return manifestdict(self, dict.copy(self._flags))
 
 class manifest(revlog.revlog):
     def __init__(self, opener):
-        self._mancache = None
+        # we expect to deal with not more than three revs at a time in merge
+        self._mancache = util.lrucachedict(3)
         revlog.revlog.__init__(self, opener, "00manifest.i")
 
     def parse(self, lines):
         mfdict = manifestdict()
         parsers.parse_manifest(mfdict, mfdict._flags, lines)
         return mfdict
 
     def readdelta(self, node):
         r = self.rev(node)
         return self.parse(mdiff.patchtext(self.revdiff(self.deltaparent(r), r)))
 
     def readfast(self, node):
         '''use the faster of readdelta or read'''
         r = self.rev(node)
         deltaparent = self.deltaparent(r)
         if deltaparent != revlog.nullrev and deltaparent in self.parentrevs(r):
             return self.readdelta(node)
         return self.read(node)
 
     def read(self, node):
         if node == revlog.nullid:
             return manifestdict() # don't upset local cache
-        if self._mancache and self._mancache[0] == node:
-            return self._mancache[1]
+        if node in self._mancache:
+            return self._mancache[node][0]
         text = self.revision(node)
         arraytext = array.array('c', text)
         mapping = self.parse(text)
-        self._mancache = (node, mapping, arraytext)
+        self._mancache[node] = (mapping, arraytext)
         return mapping
 
     def _search(self, m, s, lo=0, hi=None):
         '''return a tuple (start, end) that says where to find s within m.
 
         If the string is found m[start:end] are the line containing
         that string.  If start == end the string was not found and
         they indicate the proper sorted insertion point.
 
         m should be a buffer or a string
         s is a string'''
         def advance(i, c):
             while i < lenm and m[i] != c:
                 i += 1
             return i
         if not s:
             return (lo, lo)
         lenm = len(m)
         if not hi:
             hi = lenm
         while lo < hi:
             mid = (lo + hi) // 2
             start = mid
             while start > 0 and m[start - 1] != '\n':
                 start -= 1
             end = advance(start, '\0')
             if m[start:end] < s:
                 # we know that after the null there are 40 bytes of sha1
                 # this translates to the bisect lo = mid + 1
                 lo = advance(end + 40, '\n') + 1
             else:
                 # this translates to the bisect hi = mid
                 hi = start
         end = advance(lo, '\0')
         found = m[lo:end]
         if s == found:
             # we know that after the null there are 40 bytes of sha1
             end = advance(end + 40, '\n')
             return (lo, end + 1)
         else:
             return (lo, lo)
 
     def find(self, node, f):
         '''look up entry for a single file efficiently.
         return (node, flags) pair if found, (None, None) if not.'''
-        if self._mancache and self._mancache[0] == node:
-            return self._mancache[1].get(f), self._mancache[1].flags(f)
+        if node in self._mancache:
+            mapping = self._mancache[node][0]
+            return mapping.get(f), mapping.flags(f)
         text = self.revision(node)
         start, end = self._search(text, f)
         if start == end:
             return None, None
         l = text[start:end]
         f, n = l.split('\0')
         return revlog.bin(n[:40]), n[40:-1]
 
     def add(self, map, transaction, link, p1=None, p2=None,
             changed=None):
         # apply the changes collected during the bisect loop to our addlist
         # return a delta suitable for addrevision
         def addlistdelta(addlist, x):
             # for large addlist arrays, building a new array is cheaper
             # than repeatedly modifying the existing one
             currentposition = 0
             newaddlist = array.array('c')
 
             for start, end, content in x:
                 newaddlist += addlist[currentposition:start]
                 if content:
                     newaddlist += array.array('c', content)
 
                 currentposition = end
 
             newaddlist += addlist[currentposition:]
 
             deltatext = "".join(struct.pack(">lll", start, end, len(content))
                            + content for start, end, content in x)
             return deltatext, newaddlist
 
         def checkforbidden(l):
             for f in l:
                 if '\n' in f or '\r' in f:
                     raise error.RevlogError(
                         _("'\\n' and '\\r' disallowed in filenames: %r") % f)
 
         # if we're using the cache, make sure it is valid and
         # parented by the same node we're diffing against
-        if not (changed and self._mancache and p1 and self._mancache[0] == p1):
+        if not (changed and p1 and (p1 in self._mancache)):
             files = sorted(map)
             checkforbidden(files)
 
             # if this is changed to support newlines in filenames,
             # be sure to check the templates/ dir again (especially *-raw.tmpl)
             hex, flags = revlog.hex, map.flags
             text = ''.join("%s\0%s%s\n" % (f, hex(map[f]), flags(f))
                            for f in files)
             arraytext = array.array('c', text)
             cachedelta = None
         else:
             added, removed = changed
-            addlist = self._mancache[2]
+            addlist = self._mancache[p1][1]
 
             checkforbidden(added)
             # combine the changed lists into one list for sorting
             work = [(x, False) for x in added]
             work.extend((x, True) for x in removed)
             # this could use heapq.merge() (from Python 2.6+) or equivalent
             # since the lists are already sorted
             work.sort()
 
             delta = []
             dstart = None
             dend = None
             dline = [""]
             start = 0
             # zero copy representation of addlist as a buffer
             addbuf = util.buffer(addlist)
 
             # start with a readonly loop that finds the offset of
             # each line and creates the deltas
             for f, todelete in work:
                 # bs will either be the index of the item or the insert point
                 start, end = self._search(addbuf, f, start)
                 if not todelete:
                     l = "%s\0%s%s\n" % (f, revlog.hex(map[f]), map.flags(f))
                 else:
                     if start == end:
                         # item we want to delete was not found, error out
                         raise AssertionError(
                                 _("failed to remove %s from manifest") % f)
                     l = ""
                 if dstart is not None and dstart <= start and dend >= start:
                     if dend < end:
                         dend = end
                     if l:
                         dline.append(l)
                 else:
                     if dstart is not None:
                         delta.append([dstart, dend, "".join(dline)])
                     dstart = start
                     dend = end
                     dline = [l]
 
             if dstart is not None:
                 delta.append([dstart, dend, "".join(dline)])
             # apply the delta to the addlist, and get a delta for addrevision
             deltatext, addlist = addlistdelta(addlist, delta)
             cachedelta = (self.rev(p1), deltatext)
             arraytext = addlist
             text = util.buffer(arraytext)
 
         n = self.addrevision(text, transaction, link, p1, p2, cachedelta)
-        self._mancache = (n, map, arraytext)
+        self._mancache[n] = (map, arraytext)
 
         return n