How to limit parallel jobs

I have a hosts containing file say /tmp/hostlist which requires username & password to login and I am using expect command to login hosts and execute command and come out like below in my bash script.

#!/bin/bashexport file="/tmp/hostlist"export cmd="hostname -f"script=$(cat <<'END_OF_SCRIPT'    set timeout 120    set f $::env(file)    set fh [open $f r]    while {[gets $fh server_name] != -1} {    spawn sudo -i -u rcuser ssh $server_name    send "\r"    expect "$server_name login:"    send "root\r"    expect "Password:"    send "passwd\r"    send "$::env(cmd)\r"    send "exit\r"    expect eof    }    close $fhEND_OF_SCRIPT)VAR=$(expect -c "$script")echo "$VAR" >/tmp/outexp-----------------

I am able to handle parallel execution -

while IFS= read -r ido        ( export server_name=`echo $i`;echo "connecting to $i";expect -c "$script";echo "Job completed on $i";echo "-----------------------------------" ) >> "${log}_${i}" 2>&1 &done < "$file"waitwhile IFS= read -r ido        cat "${log}_${i}"        rm "${log}_${i}"done < "$file" > "$log2"wait

Is there a way to limit no. of hosts at a time? e.g suppose i have 1000 hosts in a file..and i want to execute in a set of 100 hosts at a time to complete 1000 hosts..