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
#require execbit unix-permissions no-chg
Checking that experimental.atomic-file works.
$ cat > $TESTTMP/show_mode.py <<EOF
> import os
> import stat
> import sys
> ST_MODE = stat.ST_MODE
>
> for file_path in sys.argv[1:]:
> file_stat = os.stat(file_path)
> octal_mode = oct(file_stat[ST_MODE] & 0o777).replace('o', '')
> print("%s:%s" % (file_path, octal_mode))
>
> EOF
$ hg init repo
$ cd repo
$ cat > .hg/showwrites.py <<EOF
> from mercurial import pycompat
> from mercurial.utils import stringutil
> def uisetup(ui):
> from mercurial import vfs
> class newvfs(vfs.vfs):
> def __call__(self, *args, **kwargs):
> print(pycompat.sysstr(stringutil.pprint(
> ('vfs open', args, sorted(list(kwargs.items()))))))
> return super(newvfs, self).__call__(*args, **kwargs)
> vfs.vfs = newvfs
> EOF
$ for v in a1 a2 b1 b2 c ro; do echo $v > $v; done
$ chmod +x b*
$ hg commit -Aqm _
# We check that
# - the changes are actually atomic
# - that permissions are correct (all 4 cases of (executable before) * (executable after))
# - that renames work, though they should be atomic anyway
# - that it works when source files are read-only (but directories are read-write still)
$ for v in a1 a2 b1 b2 ro; do echo changed-$v > $v; done
$ chmod -x *1; chmod +x *2
$ hg rename c d
$ hg commit -qm _
Check behavior without update.atomic-file
$ hg update -r 0 -q
$ hg update -r 1 --config extensions.showwrites=.hg/showwrites.py 2>&1 | grep "a1'.*wb"
('vfs open', ('a1', 'wb'), [('atomictemp', False), ('backgroundclose', True)])
$ "$PYTHON" $TESTTMP/show_mode.py *
a1:0644
a2:0755
b1:0644
b2:0755
d:0644
ro:0644
Add a second revision for the ro file so we can test update when the file is
present or not
$ echo "ro" > ro
$ hg commit -qm _
Check behavior without update.atomic-file first
$ hg update -C -r 0 -q
$ hg update -r 1
6 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ "$PYTHON" $TESTTMP/show_mode.py *
a1:0644
a2:0755
b1:0644
b2:0755
d:0644
ro:0644
Manually reset the mode of the read-only file
$ chmod a-w ro
$ "$PYTHON" $TESTTMP/show_mode.py ro
ro:0444
Now the file is present, try to update and check the permissions of the file
$ hg up -r 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ "$PYTHON" $TESTTMP/show_mode.py ro
ro:0644
# The file which was read-only is now writable in the default behavior
Check behavior with update.atomic-files
$ cat >> .hg/hgrc <<EOF
> [experimental]
> update.atomic-file = true
> EOF
$ hg update -C -r 0 -q
$ hg update -r 1 --config extensions.showwrites=.hg/showwrites.py 2>&1 | grep "a1'.*wb"
('vfs open', ('a1', 'wb'), [('atomictemp', True), ('backgroundclose', True)])
$ hg st -A --rev 1
C a1
C a2
C b1
C b2
C d
C ro
Check the file permission after update
$ "$PYTHON" $TESTTMP/show_mode.py *
a1:0644
a2:0755
b1:0644
b2:0755
d:0644
ro:0644
Manually reset the mode of the read-only file
$ chmod a-w ro
$ "$PYTHON" $TESTTMP/show_mode.py ro
ro:0444
Now the file is present, try to update and check the permissions of the file
$ hg update -r 2 --traceback
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ "$PYTHON" $TESTTMP/show_mode.py ro
ro:0644
# The behavior is the same as without atomic update