ancestor: a new algorithm that is faster for nodes near tip
Instead of walking all the way to the root of the DAG, we generate
a set of candidate GCA revs, then figure out which ones will win
the race to the root (usually without needing to traverse all the
way to the root).
In the common case of nodes that are close to each other in both
revision number and topology, this is usually a big win: it makes
"hg --time debugancestors" up to 9 times faster than the more general
ancestor function when measured on heads of the linux-2.6 hg repo.
Victory is not assured, however. The older function can still win
by a large margin if one node is much closer to the root than the
other, or by a much smaller amount if one is an ancestor of the
other.
For now, we've also got a small paranoid harness function that calls
both ancestor functions on every input and ensures that they give
equivalent answers.
Even without the checker function, the old ancestor function needs
to stay alive for the time being, as its generality is used by
context.filectx.merge.
# manifest.py - manifest revision class for mercurial
#
# Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
#
# 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, dicthelpers
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))
def flagsdiff(self, d2):
return dicthelpers.diff(self._flags, d2._flags, "")
class manifest(revlog.revlog):
def __init__(self, opener):
# 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 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)
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 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 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[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)
return n