Monday, 11 April 2016

LinkedBlockingDeque in Java

LinkedBlockingDeque is an implementation of the BlockingDeque interface and it was added in Java 6.

LinkedBlockingDeque is an optionally bounded deque and it stores its elements as linked nodes. Since it is optionally bounded so it has constructor which takes initial capacity as parameter. In case capacity is not specified it is equal to Integer.MAX_VALUE.

LinkedBlockingDeque constructors

LinkedBlockingDeque has three constructors -

  • LinkedBlockingDeque() - Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE.
  • LinkedBlockingDeque(Collection<? extends E> c) - Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.
  • LinkedBlockingDeque(int capacity) - Creates a LinkedBlockingDeque with the given (fixed) capacity.

Here note that Linked nodes are dynamically created upon each insertion unless this would bring the deque above capacity. In case initial capacity is defined then the blocking method like put(E e) will wait if necessary for space to become available.

Since elements are stored as linked nodes so most of the operation like add(), addFirst(), put(), putFirst() run in constant time (ignoring time spent blocking). Exceptions include remove(object o), removeFirstOccurrence, removeLastOccurrence, contains, iterator.remove(), and the bulk operations, all of which run in linear time.

Example code

Let's create a produce consumer bounded buffer using LinkedBlockingDeque which is an implmentation of BlockingDeque.

Values will be inserted in the LinkedBlockingDeque using put() method, which will block if the space is full.

Values will be retrieved from the LinkedBlockingDeque using take() method, which retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Here in the Produce class some delay is induced using sleep() method. You can see that in Consumer class, where it is taking elements out of the deque, no excpetion will be thrown but it will block. If you are using eclipse you can see that delay in the console when it is printing.

import java.util.concurrent.BlockingDeque;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingDeque;

public class LinkedBlockingDQDemo {
    public static void main(String[] args) {
        SharedClass buffer = new SharedClass();
        // Starting two threads
        ExecutorService executor = Executors.newFixedThreadPool(2);
        executor.execute(new Producer(buffer));
        executor.execute(new Consumer(buffer));
        executor.shutdown();

    }
}


/**
 * 
 * 
 *
 */
class Producer implements Runnable{
    SharedClass buffer;
    Producer(SharedClass buffer){
        this.buffer = buffer;
    }
    @Override
    public void run() {
        for(int i = 0; i < 10; i++){
            buffer.put(i);
            if(i == 4){
                try {
                    // introducing some delay using sleep
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

/**
 * 
 * 
 *
 */
class Consumer implements Runnable{
    SharedClass buffer;
    Consumer(SharedClass buffer){
        this.buffer = buffer;
    }
    @Override
    public void run() {
        for(int i = 0; i < 10; i++){
            buffer.get();;
        }
    }    
}

//Shared class used by threads
class SharedClass{
    int i;
    // Bounded LinkedBlockingDeque of size 10
    BlockingDeque<Integer> linkedBlockingDeque = new LinkedBlockingDeque<Integer>(10);
    
    public void get(){
       try {
            // take method to get from blockingdeque
           System.out.println("Consumer recd - " + linkedBlockingDeque.take());
       } catch (InterruptedException e) {
            // TODO Auto-generated catch block
           e.printStackTrace();
       }
    }
    
    public void put(int i){
       this.i = i;
       try {
            // putting in blocking deque
            linkedBlockingDeque.put(i);
            System.out.println("Putting - " + i);
       }
       catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
       } 
    }
}

Output

Putting - 0
Putting - 1
Putting - 2
Putting - 3
Putting - 4
Consumer recd - 0
Consumer recd - 1
Consumer recd - 2
Consumer recd - 3
Consumer recd - 4
Putting - 5
Consumer recd - 5
Putting - 6
Consumer recd - 6
Putting - 7
Consumer recd - 7
Putting - 8
Consumer recd - 8
Putting - 9
Consumer recd - 9

That's all for this topic LinkedBlockingDeque in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!


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