Re: Stumped. How to add a limit to a LinkedBlockingQueue

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 27 Aug 2006 19:48:35 GMT

Message-ID:

<nGmIg.2098$xQ1.530@newsread3.news.pas.earthlink.net>

Bogus Exception wrote:

Patricia,

Thanks again for writing. Your assistance is great!

In order for me to use a direct instantiation of LinkedBlockingQueue, I
can't use an array. This is true with or without an imposed queue
limit. This is why this approach was needed.

For example, this is OK:

final int QUEUE_SIZE = 10;
LinkedBlockingQueue<ObjectList>
qCPin = new LinkedBlockingQueue<ObjectList>(QUEUE_SIZE),
qECin = new LinkedBlockingQueue<ObjectList>(QUEUE_SIZE);

Which is great for inbound queues, which LinkedBlockingQueue allows
multiple producers by default. The trouble starts when we try:

LinkedBlockingQueue<ObjectList>[] aGout = new
LinkedBlockingQueue<ObjectList>[1];

..or even:

LinkedBlockingQueue<ObjectList>[] aGout = {qCPin};

Either yields the same error:
Cannot create a generic array of LinkedBlockingQueue<ObjectList>

The only way I found around this problem was the code you saw in my
first post, which simply inheritted from LinkedBlockingQueue. Since I
need an array of queues (one producer can send to many consumers), the
standard approaches I've seen on the net don't work (that is, where
there is one producer and one consumer). Eckel's TIJ4 code was the only
example that worked with arrays.

Take a look at this, and see if it helps:

import java.util.concurrent.LinkedBlockingQueue;

public class ArrayTest {

   public static void main(String[] args) {
     MyQueue[] quarray = new MyQueue[5];
     quarray[2] = new MyQueue();
     for(int i=0; i<7; i++){
       System.out.println(quarray[2].offer("Element "+i));
     }
   }

   static class MyQueue extends LinkedBlockingQueue<String>{
     MyQueue(){
       super(5);
     }
   }

}

Obviously, you can use any number you like instead of "5".

Patricia