#!/bin/bash

# === global variables ================================================
LOCKBASE="/var/lock"    # old
#LOCKBASE="/run/lock"   # new

# === support functions ===============================================
# --- display usage information ---------------------------------------
action_usage() {
BN=$(basename $0)
cat <<EOF
usage: ${BN} [ no-lock-test | lock-test | help ]
EOF
}

# --- display extended usage information ------------------------------
action_help() {
cat <<EOF
To be done...
EOF
}

# --- a simple test ---------------------------------------------------
action_no_lock_test() {
SECS="$1"
if [ -z "${SECS}" ]
then
        SECS="3"
fi
echo -n "TEST: about to sleep ${SECS}s..."
sleep "${SECS}"
echo " done."
}

# --- locking test ----------------------------------------------------
action_lock_test() {
LOCKFILE="$1"
CALLFUNC="$2"
shift
shift
if [ -z "${LOCKFILE}" ]
then
        echo "Error: no lockfile name specified!" >&2
        exit 1
fi
if [ -z "${CALLFUNC}" ]
then
        echo "Error: no function to call specified!" >&2
        exit 1
fi
# - - locking section - begin - - - - - - - - - - - - - - - - - - - - -
(
        flock -x -n 234
        if [ "$?" = "0" ]
        then
                # call the important function within the locked context
                "${CALLFUNC}" $*
                # clear lockfile, because we must have created it
                rm "${LOCKFILE}"
                # don't do any important stuff here
                exit 0
        else
                echo "Error: Failed to acquire lock!" >&2
                exit 1
        fi
) 234>"${LOCKFILE}"
# - - locking section - end - - - - - - - - - - - - - - - - - - - - - -
}

# === main entry point ================================================
case $1 in
nt|no-lock-test)
        shift
        action_no_lock_test $1
;;
lt|lock-test)
        shift
        action_lock_test "${LOCKBASE}/script-lock-test.lck" "action_no_lock_test" "$1"
;;
help)
        action_usage
        action_help
;;
*)
        action_usage
        exit 1
;;
esac

exit 0

# --- end of file ---