named pipe queues.sh

#!/bin/sh

# clear old pipe and lock
rmdir worklock 2>/dev/null
rm work

if [[ ! -p work ]]; then
  mkfifo work
else
  dd if=work of=/dev/null
fi


# define a worker loop

function worker {
  workerid=$1
  job=""
  while [[ $job != "quit" ]] ; do
    
    # acquire a really naive lock so we don't race others for the fifo
    if mkdir worklock 2>/dev/null ; then
      
      # read the job off the pipe
      read job < work
      
      # unlock the queue so others can work
      rmdir worklock
      
      # do the work
      case "$job" in
        "quit")
          echo "worker $workerid: quitting"
          ;;
        *)
          echo "worker $workerid: $job"
          sleep 3 # simulate work
          ;;
      esac
    else
      # failed to get the lock, wait and try again
      sleep 0.01
    fi
    
  done
}

# start two workers

worker 1 &
worker 2 &
worker 3 &
worker 4 &

# send them jobs

function queue {
  echo $* >> work
  sleep 0.01
}

queue "job 1"
queue "job 2"
queue "job 3"
queue "job 4"
queue "job 5"
queue "job 6"

queue "quit"
queue "quit"
queue "quit"
queue "quit"