tame/bin/tamed

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#!/bin/bash
# Daemon for accepting TAME commands (compilers, linker, etc)
#
# Copyright (C) 2018 R-T Specialty, LLC.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
##
set -euo pipefail
declare -r mypath=$( dirname "$( readlink -f "$0" )" )
declare -ri EX_RUNNING=1
declare -ri EX_USAGE=64 # incorrect usage; sysexits.h
declare -ri EX_CANTCREAT=73 # cannot create file; sysexits.h
# number of seconds of output silence before runners are considered unused
# and are subject to termination (see stall-monitor)
declare -ri TAMED_STALL_SECONDS="${TAMED_STALL_SECONDS:-1}"
# id of process that indirectly spawned tamed (default $PPID)
declare -ri TAMED_SPAWNER_PID="${TAMED_SPAWNER_PID:-$PPID}"
# set by `main', global for `cleanup'
declare root=
# Create FIFOs for runner
#
# The FIFOs are intended to be attached to stderr and stdout
# of the runner and will be created relative to the given
# root path ROOT.
#
# If a FIFO cannot be created, exit with EX_CANTCREAT.
mkfifos()
{
local -r root="${1?Missing root path}"
mkdir -p "$root"
# note that there's no stderr; see `add-runner'
for n in 0 1; do
rm -f "$root-$n"
mkfifo -m 0600 "$root/$n" || {
echo "fatal: failed to create FIFO at $in"
exit $EX_CANTCREAT
}
done
# keep FIFOs open so we don't get EOF from writers
tail -f >"$root/0" &
}
# Spawn a runner
#
# A new runner is created by spawning dslc and attaching
# new FIFOs under the given id ID relative to the given
# run path ROOT. The PID of the runner will be stored
# alongside the FIFOs in a pidfile `pid'.
spawn-runner()
{
local -ri id="${1?Missing id}"
local -r root="${2?Missing root run path}"
local -r base="$root/$id"
mkfifos "$base"
# monitor runner usage and kill when inactive
stall-monitor "$base" &
# loop to restart runner in case of crash
while true; do
declare -i job=0
trap 'kill -INT $job' HUP
"$mypath/dslc" < "$base/0" &> "$base/1" & job=$!
declare -i status=0
wait -n 2>/dev/null || status=$?
echo "warning: runner $id exited with code $status; restarting" >&2
done &
echo "$!" > "$base/pid"
echo "runner $id ($!): $base"
}
# Kill runner at BASE when it becomes inactive for TAMED_STALL_SECONDS
# seconds
#
# This monitors the modification time on the stdout FIFO. stdin does not
# need to be monitored since dslc immediately echoes back commands it
# receives.
#
# dslc is pretty chatty at the time of writing this, so TAMED_STALL_SECONDS
# can easily be <=30s even for large packages. This may need to change in
# the future if it becomes too much less chatty. Increase that environment
# variable if runners stall unexpectedly in the middle of builds.
#
# If the id of the spawning process has been provided then we will never
# consider ourselves to be stalled if that process is still running. This
# prevents, for example, tamed from killing itself while a parent make
# process is still running.
stall-monitor()
{
local -r base="${1?Missing base}"
# monitor output FIFO modification time
while true; do
local -i since=$( date +%s )
sleep "$TAMED_STALL_SECONDS"
local -i last=$( stat -c%Y "$base/1" )
# keep waiting if there has been activity since $since
test "$last" -le "$since" || continue
spawner-dead || continue
# no activity; kill
local -r pid=$( cat "$base/pid" )
kill "$pid"
wait "$pid" 2>/dev/null
# this stall subprocess is no longer needed
break
done
}
# Check to see if the spawning process has died
#
# If no spawning process was provided, then this always returns a zero
# status. Otherwise, it returns whether the given pid is _not_ running.
spawner-dead()
{
test "$TAMED_SPAWNER_PID" -gt 0 || return 0
! ps "$TAMED_SPAWNER_PID" &>/dev/null
}
# Exit if tamed is already running at path ROOT
#
# If tamed is already running at ROOT, exit with status
# EX_RUNNING; otherwise, do nothing except output a warning
# if a stale pid file exists.
abort-if-running()
{
local -r root="${1?Missing root rundir}"
local -ri pid=$( cat "$root/pid" 2>/dev/null )
test "$pid" -gt 0 || return 0
! ps "$pid" &>/dev/null || {
echo "fatal: tamed is already running at $root (pid $pid)!"
exit $EX_RUNNING
}
test -z "$pid" || {
echo "warning: clearing stale tamed (pid $pid)"
}
}
# Kill running tamed at path ROOT
#
# If no pidfile is found at ROOT, do nothing. This sends a
# signal only to the parent tamed process, _not_ individual
# runners; the target tamed is expected to clean up itself.
# Consequently, if a tamed terminated abnormally without
# cleaning up, this will not solve that problem.
kill-running()
{
local -r root="${1?Missing root}"
local -r pid=$( cat "$root"/pid 2>/dev/null )
test -n "$pid" || return 0
echo "killing tamed at $root ($pid)..."
kill "$pid"
}
# Clean up child processes before exit
#
# This should be called before exit (perhaps by a trap). Kills
# the entire process group.
#
# Do not attach this to a SIGTERM trap or it will infinitely
# recurse.
cleanup()
{
rm -rf "$root"
kill 0
}
# Output usage information and exit
usage()
{
cat <<EOF
Usage: $0 [--kill] [runpath]
Start tamed and runners. Do not fork into background process.
The default value of RUNPATH is \`/run/user/$UID/tamed'.
Only one runner is currently supported. tamed exits once all
runners have terminated. Runners will be killed once they are
inactive for at least TAMED_STALL_SECONDS (default 1), unless
the process identified by TAMED_SPAWNER_PID is still running.
For example, a build script may wish to set TAMED_SPAWNER_PID
to the process id of make itself. It defaults to the actual
parent process id (PPID), so tamed will not kill itself if
run manually on a shell (unless the shell exits first).
Options:
--help show this message
--kill kill a runing tamed at path RUNPATH
Environment Variables:
TAMED_STALL_SECONDS number of seconds of runner inactivity before
runner is automatically killed (default 1)
TAMED_SPAWNER_PID inhibit stalling while this process is running
(default PPID)
EOF
exit $EX_USAGE
}
# Run tamed
main()
{
local kill=
case "${1:-}" in
--kill) kill=1; shift;;
--help) usage;;
esac
root="${1:-/run/user/$UID/tamed}"
# kill if requested
test -z "$kill" || {
kill-running "$root"
exit
}
abort-if-running "$root"
# clean up background processes before we exit
trap exit TERM
trap cleanup EXIT
# start fresh
rm -rf "$root"; mkdir -p "$root"
echo $$ > "$root/pid"
# only a single runner for now
spawn-runner 0 "$root"
wait -n
}
main "$@"