在计时器中启动多个线程

Question

I came here for an answer of question which keeps me busy for a longer time.

For clarity, this is what I am doing:

I am creating a java program, which keeps an eye on datas in PLC in form of Graph. Being more specific, I am running a single Timer with TimerTask, which keeps loading data from that PLC every period. But here comes the main problem - a single variable readed from data block takes about 250ms. I want to read more variables at the same time. So basically, it takes variables*250ms in time. I think that threading here would be absolutely necessary to achieve dreamed goals.

Come little more deeper into the code:

From the beginning. I am starting a Timer as this:

Timer timer = new Timer();
timer.schedule(dc, 0, period);

Where the dc is instance of a DataCollector class, which gets the data from PLC. A vital fragment of method run() in DataCollector is like this:

@Override
public void run() {
    variables = readFromPlc();

And here comes the problem I am standing at. readFromPlc calls read() from another class called TCP. In that class, I am creating as many threads as are variables. But the problem is how to keep those threads running in period of time!. I create those Threads in constructor and at the first time, they of course call run() and properly read datas from plc and show them to a graph. But that's end of those threads - run() won't be called again.

If i could stop and continue threads repeatedly, that would be great. But I am structed here. PS: I can't simple make a new instance of TCP, because I have some other methods and functional code there which I don't want to run again.

OR very simplyfied: I want to run threads' run method every period of time (fe every second).

I would appreciate any help.

Thanks, Michael

Answer 1

As mentioned in the comment, a suggestion about how this might possibly be done using an ExecutorService

EDIT/NOTE : This example only shows the basic approach. In the real application, you'd have to make sure that shutdown() is called on the ExecutorService once it is no longer required (or alternatively, allow the core threads to time out).

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ScheduledMultiThread
{
    public static void main(String[] args)
    {
        Timer timer = new Timer();
        long period = 1000;

        DataCollector dc = new DataCollector();
        timer.schedule(dc, 0, period);


    }
}

class DataCollector extends TimerTask
{
    private ExecutorService executorService;

    @Override
    public void run()
    {
        int variables = readFromPlc();
        if (executorService == null)
        {
            executorService = Executors.newFixedThreadPool(variables);
        }

        List<Callable<Object>> tasks = new ArrayList<Callable<Object>>();
        for (int i=0; i<variables; i++)
        {
            Runnable task = createTaskForVariable(i);
            tasks.add(Executors.callable(task));
        }
        try
        {
            executorService.invokeAll(tasks);
        }
        catch (InterruptedException e)
        {
            Thread.currentThread().interrupt();
        }
    }

    private Runnable createTaskForVariable(final int variable)
    {
        Runnable runnable = new Runnable()
        {
            @Override
            public void run()
            {
                executeTaskFor(variable);
            }
        };
        return runnable;
    }


    // Dummy implementations
    private void executeTaskFor(int variable)
    {
        System.out.println("Working for variable "+variable);
        try
        {
            Thread.sleep((long)(200+Math.random()*200));
        }
        catch (InterruptedException e)
        {
            Thread.currentThread().interrupt();
        }
        System.out.println("Working for variable "+variable+" DONE");
    }

    private int readFromPlc()
    {
        return 8;
    }


}