Inter-process communication without FIFOs

Question

Inside a BASH script we can have multiple processes running in background which intercommunicate using named pipes, FIFOs registered on the filesystem. An example of this could

Answer 1

Have you considered the use of signals? If the only thing you need is to trigger an event (without passing arguments), using kill and trap works perfectly (be careful of the semantics though, use SIGUSR1 for instance).

You might need to rework the logic though, as in the example below:

subprocess_finished()
{
    np=$( jobs -p | wc -l )
}

start_processing()
{
    myfile="$1"
    # DO SOMETHING HERE!!
    kill -SIGUSR1 $2
}

CPUS=$( lscpu | grep "^CPU(s):" | rev | cut -f 1 -d ' ' | rev )
POLLPERIOD=5  # 5s between each poll
np=0
trap subprocess_finished SIGUSR1

for myfile in *
do 
        start_processing "$myfile" $$ &
        np=$( jobs -p | wc -l )
        echo "$( date +'%Y-%m-%d %H:%M:%S' ) [$!] Starting #$np on $CPUS: $myfile"

        if [ $np -eq $CPUS ] 
        then
            # Wait for one CPU to be free
            trap subprocess_finished SIGUSR1
            while [ $np -eq $CPUS ]
            do
                sleep $POLLPERIOD
            done
        fi
    done
done

# wait for the last subprocesses
while [ ! -z "$( jobs -rp )" ]
do
    sleep $POLLPERIOD
done