Mercurial > hg
view rust/chg/src/sendfds.c @ 49491:c6a1beba27e9
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
author | Arun Kulshreshtha <akulshreshtha@janestreet.com> |
---|---|
date | Tue, 30 Aug 2022 15:29:55 -0400 |
parents | 208cb7a9d0fa |
children |
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/* * Utility to send fds via Unix domain socket * * Copyright 2011, 2018 Yuya Nishihara <yuya@tcha.org> * * This software may be used and distributed according to the terms of the * GNU General Public License version 2 or any later version. */ #include <errno.h> #include <stdlib.h> #include <string.h> #include <sys/socket.h> #include <sys/types.h> #define MAX_FD_LEN 10 /* * Sends the given fds with 1-byte dummy payload. * * Returns the number of bytes sent on success, -1 on error and errno is set * appropriately. */ ssize_t sendfds(int sockfd, const int *fds, size_t fdlen) { char dummy[1] = {0}; struct iovec iov = {dummy, sizeof(dummy)}; char fdbuf[CMSG_SPACE(sizeof(fds[0]) * MAX_FD_LEN)]; struct msghdr msgh; struct cmsghdr *cmsg; /* just use a fixed-size buffer since we'll never send tons of fds */ if (fdlen > MAX_FD_LEN) { errno = EINVAL; return -1; } memset(&msgh, 0, sizeof(msgh)); msgh.msg_iov = &iov; msgh.msg_iovlen = 1; msgh.msg_control = fdbuf; msgh.msg_controllen = CMSG_SPACE(sizeof(fds[0]) * fdlen); cmsg = CMSG_FIRSTHDR(&msgh); cmsg->cmsg_level = SOL_SOCKET; cmsg->cmsg_type = SCM_RIGHTS; cmsg->cmsg_len = CMSG_LEN(sizeof(fds[0]) * fdlen); memcpy(CMSG_DATA(cmsg), fds, sizeof(fds[0]) * fdlen); msgh.msg_controllen = cmsg->cmsg_len; return sendmsg(sockfd, &msgh, 0); }