Forking / Multi-Threaded Processes | Bash

Question

I would like to make a section of my code more efficient. I'm thinking of making it fork off into multiple processes and have them execute 50/100 times at once, instead of just once.

For example (pseudo):

for line in file; do  foo; foo2; foo3; done 

I would like this for loop to run multiple times. I know this can be done with forking. Would it look something like this?

while(x <= 50) parent(child pid) {    fork child() } child {    do     foo; foo2; foo3;     done    return child_pid() } 

Or am I thinking about this the wrong way?

Thanks!

Answer 1

In bash scripts (non-interactive) by default JOB CONTROL is disabled so you can't do the the commands: job, fg, and bg.

Here is what works well for me:

#!/bin/sh  set -m # Enable Job Control  for i in `seq 30`; do # start 30 jobs in parallel   sleep 3 & done  # Wait for all parallel jobs to finish while [ 1 ]; do fg 2> /dev/null; [ $? == 1 ] && break; done 

The last line uses "fg" to bring a background job into the foreground. It does this in a loop until fg returns 1 ($? == 1), which it does when there are no longer any more background jobs.