CODEWITHSUNDEEP
javamultithreading
ThatGuy343
ThatGuy343

Reputation: 2424

Multi threaded for loop

Im trying to take a for loop like this:

List<Object> users;

public void doSomething() {

    for (Object o : users) {

    // split up the for loop
    // and handle chunks of the iteration
    // across multiple threads

        o.doThis();
        o.doThat();
    }
}

And divide the iteration for(Object o: users){ into multiple threads. How can I do this with Java while not causing concurrent modifications. My goal is to scale this like a thread pool, so the more objects in List<Object> users; means more threads handling a chunk of the iteration.

I am new to multithreading and am not sure what java utils could help accomplish this.

Upvotes: 2

Views: 587

Answers (2)

Saurabh Jhunjhunwala
Saurabh Jhunjhunwala

Reputation: 2922

You can use java.util.concurrent.Executors class which would assist you in executing multiple thread concurrently.

Have written a small method, which can assist your understanding.

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SimpleThreadPool {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++) {
            Runnable worker = new WorkerThread("" + i);
            executor.execute(worker);
          }
        executor.shutdown();
        while (!executor.isTerminated()) {

        }
        System.out.println("Finished all threads");
    }

}



public class WorkerThread implements Runnable {

    private String command;

    public WorkerThread(String s){
        this.command=s;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+" Start. Command = "+command);
        processCommand();
        System.out.println(Thread.currentThread().getName()+" End.");
    }

    private void processCommand() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public String toString(){
        return this.command;
    }
}

Upvotes: 1

yxre
yxre

Reputation: 3704

If you are using java 8, streams would be the simplest way

users.parallelStream()
                .forEach(u -> { u.doThis(); u.doThat(); } );

You could also implement a runnable interface, and create a ThreadExecutor. This would be much more code than the above example.

Upvotes: 2

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