uglylock

#!/usr/bin/env sh

# $1 lock file
function set_lockfile()
{
    set -o noclobber
    printf $PPID > "$1" 2>/dev/null && return 0

    locked_pid=$(< "$1")
    [ $locked_pid -gt "0" ] || return 1
    kill -0 $locked_pid 2>/dev/null && return 1
    
    rm "$1" 2>/dev/null
    printf "$PPID" > "$1" 2>/dev/null && return 0
    return 1
}

# $1 timeout
# $2 lock file
function set_lockfile_wait()
{
    declare -ir start_time=$(date '+%s')
    declare -ir timeout="${1:-0}"

    while ! set_lockfile "$2" 2>/dev/null
    do
        if [ $(($(date '+%s') - $start_time)) -ge $timeout ] ; then
            printf "Error: waited too long for lock file %s\n" "$2" 1>&2
            return 1
        fi
        sleep 1
    done

    return 0
}

# $1 lock file
function release_lockfile()
{
    [ -e "$1" ] && grep -Fxq $PPID "$1" && rm -f "$1"
}

function print_usage()
{
    printf "%s [-h][-t n][-u] <lock file>\n" $(basename "$0")
}

POSITIONAL=()
while [[ $# -gt 0 ]]
do
    key="$1"

    case $key in
        -h|--help)
            print_usage
            exit 0
            ;;
        -t|--timeout)
            declare -ir TIMEOUT=$2
            shift
            shift
            ;;
        -u|--unlock)
            UNLOCK=true
            shift
            ;;
        *)
            POSITIONAL+=("$1")
            shift
            ;;
    esac
done
set -- "${POSITIONAL[@]}"

if [ "$UNLOCK" = true ]
then
    release_lockfile "$1"
    exit 0
fi

if ! set_lockfile_wait ${TIMEOUT:-0} "$1"  ; then
    exit 1
fi

exit 0