bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
revlog.parseindex must be able to parse the index file even if
an index entry is split between two 64k blocks. The ideal test
would be to create an index file with inline data where
64k < size < 64k + 64 (64k is the size of the read buffer, 64 is
the size of an index entry) and with an index entry starting right
before the 64k block boundary, and try to read it.
We approximate that by reducing the read buffer to 1 byte.
$ hg init a
$ cd a
$ echo abc > foo
$ hg add foo
$ hg commit -m 'add foo'
$ echo >> foo
$ hg commit -m 'change foo'
$ hg log -r 0:
changeset: 0:7c31755bf9b5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add foo
changeset: 1:26333235a41c
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change foo
$ cat >> test.py << EOF
> from mercurial import changelog, node, pycompat, vfs
>
> class singlebyteread(object):
> def __init__(self, real):
> self.real = real
>
> def read(self, size=-1):
> if size == 65536:
> size = 1
> return self.real.read(size)
>
> def __getattr__(self, key):
> return getattr(self.real, key)
>
> def __enter__(self):
> self.real.__enter__()
> return self
>
> def __exit__(self, *args, **kwargs):
> return self.real.__exit__(*args, **kwargs)
>
> def opener(*args):
> o = vfs.vfs(*args)
> def wrapper(*a, **kwargs):
> f = o(*a, **kwargs)
> return singlebyteread(f)
> wrapper.options = o.options
> return wrapper
>
> cl = changelog.changelog(opener(b'.hg/store'))
> print(len(cl), 'revisions:')
> for r in cl:
> print(pycompat.sysstr(node.short(cl.node(r))))
> EOF
$ "$PYTHON" test.py
2 revisions:
7c31755bf9b5
26333235a41c
$ cd ..
#if no-pure
Test SEGV caused by bad revision passed to reachableroots() (issue4775):
$ cd a
$ "$PYTHON" <<EOF
> from mercurial import changelog, vfs
> cl = changelog.changelog(vfs.vfs(b'.hg/store'))
> print('good heads:')
> for head in [0, len(cl) - 1, -1]:
> print('%s: %r' % (head, cl.reachableroots(0, [head], [0])))
> print('bad heads:')
> for head in [len(cl), 10000, -2, -10000, None]:
> print('%s:' % head, end=' ')
> try:
> cl.reachableroots(0, [head], [0])
> print('uncaught buffer overflow?')
> except (IndexError, TypeError) as inst:
> print(inst)
> print('good roots:')
> for root in [0, len(cl) - 1, -1]:
> print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root])))
> print('out-of-range roots are ignored:')
> for root in [len(cl), 10000, -2, -10000]:
> print('%s: %r' % (root, cl.reachableroots(root, [len(cl) - 1], [root])))
> print('bad roots:')
> for root in [None]:
> print('%s:' % root, end=' ')
> try:
> cl.reachableroots(root, [len(cl) - 1], [root])
> print('uncaught error?')
> except TypeError as inst:
> print(inst)
> EOF
good heads:
0: [0]
1: [0]
-1: []
bad heads:
2: head out of range
10000: head out of range
-2: head out of range
-10000: head out of range
None: (an integer is required( .got type NoneType.)?|'NoneType' object cannot be interpreted as an integer) (re)
good roots:
0: [0]
1: [1]
-1: [-1]
out-of-range roots are ignored:
2: []
10000: []
-2: []
-10000: []
bad roots:
None: (an integer is required( .got type NoneType.)?|'NoneType' object cannot be interpreted as an integer) (re)
$ cd ..
Test corrupted p1/p2 fields that could cause SEGV at parsers.c:
$ mkdir invalidparent
$ cd invalidparent
$ hg clone --pull -q --config phases.publish=False ../a limit --config format.sparse-revlog=no
$ hg clone --pull -q --config phases.publish=False ../a neglimit --config format.sparse-revlog=no
$ hg clone --pull -q --config phases.publish=False ../a segv --config format.sparse-revlog=no
$ rm -R limit/.hg/cache neglimit/.hg/cache segv/.hg/cache
$ "$PYTHON" <<EOF
> data = open("limit/.hg/store/00changelog.i", "rb").read()
> poisons = [
> (b'limit', b'\0\0\0\x02'),
> (b'neglimit', b'\xff\xff\xff\xfe'),
> (b'segv', b'\0\x01\0\0'),
> ]
> for n, p in poisons:
> # corrupt p1 at rev0 and p2 at rev1
> d = data[:24] + p + data[28:127 + 28] + p + data[127 + 32:]
> open(n + b"/.hg/store/00changelog.i", "wb").write(d)
> EOF
$ hg -R limit debugrevlogindex -f1 -c
rev flag size link p1 p2 nodeid
0 0000 62 0 2 -1 7c31755bf9b5
1 0000 65 1 0 2 26333235a41c
$ hg -R limit debugdeltachain -c
rev p1 p2 chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio
0 2 -1 1 1 -1 base 63 62 63 1.01613 63 0 0.00000
1 0 2 2 1 -1 base 66 65 66 1.01538 66 0 0.00000
$ hg -R neglimit debugrevlogindex -f1 -c
rev flag size link p1 p2 nodeid
0 0000 62 0 -2 -1 7c31755bf9b5
1 0000 65 1 0 -2 26333235a41c
$ hg -R segv debugrevlogindex -f1 -c
rev flag size link p1 p2 nodeid
0 0000 62 0 65536 -1 7c31755bf9b5
1 0000 65 1 0 65536 26333235a41c
$ hg -R segv debugdeltachain -c
rev p1 p2 chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio
0 65536 -1 1 1 -1 base 63 62 63 1.01613 63 0 0.00000
1 0 65536 2 1 -1 base 66 65 66 1.01538 66 0 0.00000
$ cat <<EOF > test.py
> import sys
> from mercurial import changelog, pycompat, vfs
> cl = changelog.changelog(vfs.vfs(pycompat.fsencode(sys.argv[1])))
> n0, n1 = cl.node(0), cl.node(1)
> ops = [
> ('reachableroots',
> lambda: cl.index.reachableroots2(0, [1], [0], False)),
> ('compute_phases_map_sets', lambda: cl.computephases({1: {cl.node(0)}})),
> ('index_headrevs', lambda: cl.headrevs()),
> ('find_gca_candidates', lambda: cl.commonancestorsheads(n0, n1)),
> ('find_deepest', lambda: cl.ancestor(n0, n1)),
> ]
> for l, f in ops:
> print(l + ':', end=' ')
> try:
> f()
> print('uncaught buffer overflow?')
> except ValueError as inst:
> print(inst)
> EOF
$ "$PYTHON" test.py limit/.hg/store
reachableroots: parent out of range
compute_phases_map_sets: parent out of range
index_headrevs: parent out of range
find_gca_candidates: parent out of range
find_deepest: parent out of range
$ "$PYTHON" test.py neglimit/.hg/store
reachableroots: parent out of range
compute_phases_map_sets: parent out of range
index_headrevs: parent out of range
find_gca_candidates: parent out of range
find_deepest: parent out of range
$ "$PYTHON" test.py segv/.hg/store
reachableroots: parent out of range
compute_phases_map_sets: parent out of range
index_headrevs: parent out of range
find_gca_candidates: parent out of range
find_deepest: parent out of range
$ cd ..
#endif