#!/bin/bash

# lockfile.sh [-p pid] [-t timeout] lockfile_name
#     -p pid        calling process PID. This value will be
#                   writen into created lockfile. Default is 0
#     -t timeout    polling interval in seconds when checking
#                   if file already exists. Default is 1
#     lockfile_name name of created lock file

LPID=0
LSLEEP=1
LFILE=

# options parsing
# -- all except last
while test $# -ge 2
do
    LASTOPT="$1"
    shift
    case "$LASTOPT" in
        -p)
            LPID="$1"
            shift
            ;;
        -t)
            LSLEEP="$1"
            shift
            ;;
    esac
done

# -- last option - the name of lockfile
test $# -ge 1 && LFILE="$1"

LFTMP=".$LFILE-$$"

function cleanup
{
    rm -f "$LFTMP"
}

trap cleanup EXIT

# Create read only temp file 
rm -f "$LFTMP"
umask 333
echo "$LPID" > "$LFTMP" || exit 2

# Try to create hard link to file. This will work only
# if lock file is not exist.
while ! link "$LFTMP" "$LFILE" 2>/dev/null
do
    sleep $LSLEEP
done

# Lock file is created. Unlink temp file
unlink "$LFTMP"
exit 0