sleep in pure native bash without /usr/bin/sleep and without even subshell

bash_sleep.sh

#!/usr/bin/env bash
# sleep without externals or children
# and without the bash sleep builtin

# mkfifo is not exactly free, but you only do this part once.
# After that it is relatively free to call _sleep all you want even in tight loops.
sleep_fifo=/tmp/.${0//\//_}.$$.sleep.fifo
trap "rm -f $sleep_fifo" EXIT
mkfifo $sleep_fifo || { echo "$0: Error creating sleep fifo \"$sleep_fifo\"" >&2 ; exit 1 ; }
exec 9<>$sleep_fifo

_sleep () {
	local x
	read -t ${1:-1} -u 9 x
}

####################################################################
# main

for ((i=0;i<50;i++)) {
	echo "$i: sleeping 0.1 seconds"
	_sleep 0.1
}