Threads in bash?

Is it possible to use threads in bash scripts. I have a driver class in java that i'm trying to run multiple instances of at the same t开发者_开发问答ime. The only way i know to do this is make threads in bash, but i'm not sure if thats even possible. Any help would be appreciated

Bash doesn't support threading per se, but you could launch multiple java processes in the background, like:

java myprog &
java myprog &
java myprog &

Anything more than that you might look into Python or Ruby, which have thread management utilities, you could wait for each one to finish and collect output/exit status, etc.

Edit: Borrowing the suggestion from @CédricJulien to use wait, here's a more thorough example. Given this MyProg.java program:

public class MyProg {
    public static void main(String[] args) {
        System.exit(Integer.parseInt(args[0]));
    }
}

you could write the following bash-threads.sh script to launch multiple instances of it in parallel:

#!/bin/bash
set -o errexit

java MyProg 1 &
pid1=$!
java MyProg 0 &
pid2=$!
java MyProg 2 &
pid3=$!

wait $pid1 && echo "pid1 exited normally" || echo "pid1 exited abnormally with status $?"
wait $pid2 && echo "pid2 exited normally" || echo "pid2 exited abnormally with status $?"
wait $pid3 && echo "pid3 exited normally" || echo "pid3 exited abnormally with status $?"

Its output is:

pid1 exited abnormally with status 1
pid2 exited normally
pid3 exited abnormally with status 2

You won't be able to launch some "bash threads", but you can launch subprocesses in bash, just using the & after the command, and it will launch it in a background process.

Call a wait after launching your processes to wait for them to be finished.

Try this

first_command &
second_command &

wait

Bash >= 4.0 supports the coproc keyword

coproc runs a command as though it was suffixed with & but allows access to it's process ID as well as stdin and stdout.

e.g.

coproc MYJOB myprog <args>

The process id of myprog is now $MYJOB_PID

An array variable $MYJOB then contains file descriptors for the job's stdout in $MYJOB[0] and stdin in $MYJOB[1]