view rust/chg/src/attachio.rs @ 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

// Copyright 2018 Yuya Nishihara <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Functions to send client-side fds over the command server channel.

use std::io;
use std::os::unix::io::AsRawFd;
use tokio_hglib::codec::ChannelMessage;
use tokio_hglib::{Connection, Protocol};

use crate::message;
use crate::procutil;

/// Sends client-side fds over the command server channel.
///
/// This works as follows:
/// 1. Client sends "attachio" request.
/// 2. Server sends back 1-byte input request.
/// 3. Client sends fds with 1-byte dummy payload in response.
/// 4. Server returns the number of the fds received.
///
/// The client-side fds may be dropped once duplicated to the server.
pub async fn attach_io(
    proto: &mut Protocol<impl Connection + AsRawFd>,
    stdin: &impl AsRawFd,
    stdout: &impl AsRawFd,
    stderr: &impl AsRawFd,
) -> io::Result<()> {
    proto.send_command("attachio").await?;
    loop {
        match proto.fetch_response().await? {
            ChannelMessage::Data(b'r', data) => {
                let fd_cnt = message::parse_result_code(data)?;
                if fd_cnt == 3 {
                    return Ok(());
                } else {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidData,
                        "unexpected attachio result",
                    ));
                }
            }
            ChannelMessage::Data(..) => {
                // just ignore data sent to uninteresting (optional) channel
            }
            ChannelMessage::InputRequest(1) => {
                // this may fail with EWOULDBLOCK in theory, but the
                // payload is quite small, and the send buffer should
                // be empty so the operation will complete immediately
                let sock_fd = proto.as_raw_fd();
                let ifd = stdin.as_raw_fd();
                let ofd = stdout.as_raw_fd();
                let efd = stderr.as_raw_fd();
                procutil::send_raw_fds(sock_fd, &[ifd, ofd, efd])?;
            }
            ChannelMessage::InputRequest(..)
            | ChannelMessage::LineRequest(..)
            | ChannelMessage::SystemRequest(..) => {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    "unsupported request while attaching io",
                ));
            }
        }
    }
}