Add pidwrap.sh

astrobee/survey_manager/scripts/pidwrap.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+
+# Copyright (c) 2023, United States Government, as represented by the
+# Administrator of the National Aeronautics and Space Administration.
+#
+# All rights reserved.
+#
+# The "ISAAC - Integrated System for Autonomous and Adaptive Caretaking
+# platform" software is licensed under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with the
+# License. You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+######################################################################
+# Usage: pidwrap.sh <command> [arg1] [arg2] ...
+
+# A wrapper that runs the specified child command with the following added features:
+# - The PID of the child is written to ${script_dir}/pid.txt when the child starts.
+# - The return code of the child is written to ${script_dir}/return_code.txt when the child exits.
+
+# The ${script_dir} variable refers to the folder containing this script. The reason we write the
+# status files to ${script_dir} is that we're assuming a controller script will create a unique
+# temp folder each time it wants to wrap a command, will copy this script to that temp folder, then
+# run the script like so:
+#   /tmp/uniq6537/pidwrap.sh cmd arg1 arg2 ...
+
+# With that context, it's logical for the script to write the status files to the same unique folder
+# so that the controller will know where to find them. This also keeps the wrapped command string
+# (which will be visible to the operator) relatively short.
+
+# Note: As an external process that doesn't own the child but can read its PID from the PID file,
+# here are some ways you could check the child status:
+# - Poll whether child is active: Check if directory '/proc/$pid` exists
+# - Wait until child finishes: Run 'tail --pid=$pid -f /dev/null'. This exits when the child exits
+#   (or immediately if the child already exited).
+# - Get more status for active child: Run 'cat /proc/$pid/status'.
+
+script_dir=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+
+# Enable bash job control (needed for fg command). It's normally disabled for non-interactive
+# scripts.
+set -m
+
+# Run child in background so we can immediately log its PID. We prefix the command with the short
+# sleep to avoid a weird edge case for commands that run very quickly, like if you use 'true' and
+# 'false' as test commands -- it appears that bash isn't fast enough to put them in the background
+# and foreground before they exit, which breaks the logic in the rest of the script.
+echo -n "pidwrap: running "
+(sleep 0.05 && exec "$@") &
+pid=$!
+echo $pid > "${script_dir}/pid.txt"
+
+# Foregrounding the child here has two effects: (1) It gives full control of the interactive
+# terminal back to the child, which is key because the child might be a command shell. (2) It makes
+# the child the current job again such that when it exits, $? is set to its return code.
+fg
+return_code=$?
+echo $return_code > "${script_dir}/return_code.txt"
+echo "pidwrap: return code $return_code"
+
+exit $return_code