CODEWITHSUNDEEP
javamultithreadingconcurrency
Sriram Sridharan
Sriram Sridharan

Reputation: 740

Java - How do I safely stop a thread in a Web App from the GUI?

Is there a way to safely and immediately stop the execution of a Thread in Java? Especially, if the logic inside the run() method of the Runnable implementation executes only a single iteration and does not regularly check for any flag that tells it to stop?

I am building a Web Application, using which a user can translate the contents of an entire document from one language to another.

Assuming the documents are extra-large, and subsequently assuming each translation is going to take a long time (say 20-25 minutes), my application creates a separate Thread for each translation that is initiated by its users. A user can see a list of active translations and decide to stop a particular translation job if he/she wishes so.

This is my Translator.java

public class Translator {
   public void translate(File file, String sourceLanguage, String targetLanguage) {
    //Translation happens here
    //.......
    //Translation ends and a new File is created.
   }

}

I have created a TranslatorRunnable class which implements the Runnable interface as follows:

public class TranslatorRunnable implements Runnable {

    private File document;
    private String sourceLanguage;
    private String targetLanguage;

    public TranslatorRunnable(File document, String sourceLanguage, String targetLanguage) {
        this.document = document;
        this.sourceLanguage = sourceLanguage;
        this.targetLanguage = targetLanguage;
    }

    public void run() {
        // TODO Auto-generated method stub
        Translator translator = new Translator();
        translator.translate(this.document, this.sourceLanguage, this.targetLanguage);
        System.out.println("Translator thread is finished.");
    }

}

I'm creating the thread for translating a document from an outer class like this:

TranslatorRunnable tRunnable = new TranslatorRunnable(document, "ENGLISH", "FRENCH");
Thread t = new Thread(tRunnable);
t.start();

Now my problem is how do I stop a translation process (essentially a Thread) when the user clicks on "Stop" in the GUI?

I have read a few posts on StackOverflow as well as on other sites, which tell me to have a volatile boolean flag inside the Runnable implementation, which I should check on regularly from inside the run() method and decide when to stop. See this post

This doesn't work for me as the run() method is just calling the Translator.translate() method, which itself is going to take a long time. I have no option here.

The next thing I read is to use ExecutorService and use its shutDownAll() method. But even here, I'd have to handle InterruptedException somewhere regularly within my code. This, is again out of the option. Referred this documentation of the ExecutorService class.

I know I cannot use Thread.stop() as it is deprecated and may cause issues with objects that are commonly used by all threads.

What options do I have?

Is my requirement really feasible without substantial changes to my design? If yes, please tell me how.

If it is absolutely necessary for me to change the design, could anyone tell me what is the best approach I can take?

Thanks, Sriram

Upvotes: 3

Views: 433

Answers (2)

urag
urag

Reputation: 1258

If you are the one that created the Translator class what's stopping you from adding some kind of value inside the function that is checked periodically and if needed stops reading the lines from file something like this

   public static List<String> readFile(String filename)
{
    List<String> records = new ArrayList<>();
    try
    {
        BufferedReader reader = new BufferedReader(new FileReader(filename));
        String line;
        while ((line = reader.readLine()) != null)
        {
            String[] split = line.split("\\s+");
            records.addAll(Arrays.asList(split));
            if (needsToStop) {
                break; //Or throw exception
            }
        }
        reader.close();
        return records;
    }
    catch (Exception e)
    {
        System.err.format("Exception occurred trying to read '%s'.", filename);
        e.printStackTrace();
        return null;
    }
}

Upvotes: 0

Jose Zevallos
Jose Zevallos

Reputation: 725

Is there a way to safely and immediately stop the execution of a Thread in Java?

No. each thread is reponsible to periodically check if it has been interrupted to exit as soon as possible

if (Thread.currentThread().isInterrupted() ) {
  // release resources. finish quickly what it was doing
}

if you want a more responsive application, you have to change the logic (for example divide each job in smaller batches) so each thread does this checking more often than every 20-25 minutes

Upvotes: 2

Related Questions