CODEWITHSUNDEEP
javajavafxconcurrencyparallel-processingtask
Big Lebowski
Big Lebowski

Reputation: 131

JavaFX multiple tasks

Can someone please help me out? I have a program which uses JavaFX. Now after pressing a button I want to do n-calculations. Those calculations should be done using threads (parallel) and they should NOT make the main JavaFX app hang / freeze. What I want to do, is to display a loading state while the calcuations are running and if all tasks have finished calculating, I want to continue with the program (remove the loading state and show results).

After reading some stuff about the "Concurrency in JavaFX" I came up with this:

for (int i = 0; i < n; ++i) {
    CalcTask task = new CalcTask(i);

    task.setOnSucceeded(e -> {
        // process is just a static method in which I count 
        // how many results (i) I already received 
        // (where n is the required amount). If i == n,
        // I know I am done with all the tasks
        process(task.getValue());
    });

    new Thread(task).start();
}

And the CalcTask Class:

public class CalcTask extends Task<Integer> {
    protected int id;

    public CalcTask (int id) {
        this.id = id;
    }

    @Override
    public Integer call() {
        return CALCULATION_RESULT;
    }
}

Now my question is: This seems a bit "cluncky" to me. Is there any better way for implementing stuff like this in JavaFX? Thanks :)

Upvotes: 1

Views: 1177

Answers (2)

Przemek Krysztofiak
Przemek Krysztofiak

Reputation: 924

In my opinion the better way is RxJavaFx
This sample: https://github.com/pkrysztofiak/rxjavafx-demo
RxJavaFx tutorial https://github.com/ReactiveX/RxJavaFX

package com.github.pkrysztofiak.rxjavafx.rxjavafxdemo.concurrency;

import java.util.Random;

import io.reactivex.Observable;
import io.reactivex.rxjavafx.observables.JavaFxObservable;
import io.reactivex.rxjavafx.schedulers.JavaFxScheduler;
import io.reactivex.schedulers.Schedulers;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class ParallelTasksApp extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        Button button = new Button("Start");
        Label label = new Label();
        HBox hBox = new HBox(button, label);
        stage.setScene(new Scene(hBox));
        stage.show();

        JavaFxObservable.actionEventsOf(button)
        .flatMap(actionEvent -> Observable.range(1, 4))
        .flatMap(i -> Observable.just(i)
                .subscribeOn(Schedulers.newThread())
                .map(this::runLongProcess))
        .observeOn(JavaFxScheduler.platform())
        .scan(0, (aggregator, next) -> ++aggregator)
        .map(String::valueOf)
        .subscribe(label::setText);
    }

    private int runLongProcess(int i) {
        try {
            Thread.sleep(new Random().nextInt(10000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + " i=" + i);
        return i;
    }
}

Upvotes: 0

Alexei Kaigorodov
Alexei Kaigorodov

Reputation: 13525

Since you extend class Task, you can also overwrite method succeeded() and remove invocation of task.setOnSucceeded() on the main thread:

for (int i = 0; i < n; ++i) {
  CalcTask task = new CalcTask(i);
  new Thread(task).start();
}

public class CalcTask extends Task<Integer> {
    protected int id;

    public CalcTask (int id) {
        this.id = id;
    }

    public void succeeded() {
       process(this.getValue());
    }

    @Override
    public Integer call() {
        return CALCULATION_RESULT;
    }
}

or even use plain Runnable instead of Task:

public class CalcTask implements Runnable {
    protected int id;

    public CalcTask (int id) {
        this.id = id;
    }

    @Override
    public void run() {
       CALCULATION_RESULT = calculate();
       process(CALCULATION_RESULT);
    }
}

Upvotes: 3

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