revlog: add a C implementation of `headrevsdiff`
Python implementation of `headrevsdiff` can be very slow in the worst
case compared with the `heads` computation it replaces, since the
latter is done in C.
Even the average case of this Python implementation is still
noticeable in the profiles.
This patch makes the computation much much faster by doing it in C.
#require serve repobundlerepo
$ hg init server
$ cd server
$ cat >> .hg/hgrc << EOF
> [extensions]
> strip=
> EOF
$ echo 1 > foo
$ hg commit -A -m 'first'
adding foo
$ echo 2 > bar
$ hg commit -A -m 'second'
adding bar
Produce a bundle to use
$ hg strip -r 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
saved backup bundle to $TESTTMP/server/.hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg
Serve from a bundle file
$ hg serve -R .hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg -d -p $HGPORT --pid-file=hg.pid
$ cat hg.pid >> $DAEMON_PIDS
Ensure we're serving from the bundle
$ (get-with-headers.py localhost:$HGPORT 'file/tip/?style=raw')
200 Script output follows
-rw-r--r-- 2 bar
-rw-r--r-- 2 foo