#
# protect from concurrent runs
# run this at the beginning of the critical section
#

source ~/lib/sh/include
require freturn

# pass it the name of the lockfile
#
# freturns the temporary lockedfile name
# (save this value for `put_lock()')
#
get_lock ()
{
        local +i unlocked=$1
        local +i locked=`mktemp /tmp/$$.XXXXXXXXXXXXXXXX`

        # rename(2) should be atomic, so this should prevent
        # a race with any other instances as long as we move
        # it back when we're done doing work
        #
        # XXX TODO default to 3000 busyloop iterations:
        # change to usleep? make user-settable?
        #
        for ((i = 0; i < 3000; i++)); do
                mv $unlocked $locked &>/dev/null && {
                        freturn $locked
                        return
                }
        done

        return 1
}
# vim:syn=sh:ft=sh