LinkedTransferQueue hasWaitingConsumer() method in Java

Last Updated : 03 Jan, 2019

The Java.util.concurrent.LinkedTransferQueue.hasWaitingConsumer() method always returns true if there is at least one consumer in the queue waiting to receive an element via BlockingQueue.take() or timed poll. The returned value represents a momentary state of affairs.

Syntax

public boolean hasWaitingConsumer()

Parameters: It does not take in any parameter.

Return Value: This method returns a boolean value which is true if at least one consumer is present in the queue.

Below are a few examples to illustrate the LinkedTransferQueue.hasWaitingConsumer() method:

Example 1:

// Java code to demonstrate 
// hasWaitingConsumer() method 
  
import java.util.concurrent.LinkedTransferQueue; 
  
class GFG { 
    public static void main(String args[]) 
    { 
        LinkedTransferQueue<String> LTQ 
            = new LinkedTransferQueue<String>(); 
  
        LTQ.add("Geeks"); 
        LTQ.add("For"); 
        LTQ.add("Geeks"); 
        LTQ.add("GeeksForGeeks"); 
  
        System.out.println(LTQ.hasWaitingConsumer()); 
    } 
} 

Output:

false

Example 2:

// Java code to demonstrate 
// hasWaitingConsumer() method 
  
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.LinkedTransferQueue; 
  
public class GFG { 
  
    LinkedTransferQueue<Integer> LTQ 
        = new LinkedTransferQueue<>(); 
  
    class LTQProducer implements Runnable { 
  
        @Override
        public void run() 
        { 
            for (int i = 0; i < 3; i++) { 
                try { 
                    System.out.println("Producer is"
                                       + " waiting to transfer"); 
                    LTQ.transfer(i); 
                    System.out.println("Producer transferred"
                                       + " element: "
                                       + i); 
                    System.out.println("Is there any consumer"
                                       + " still waiting to"
                                       + " receive an element"
                                       + " after transfer -> "
                                       + LTQ.hasWaitingConsumer()); 
                } 
                catch (InterruptedException e) { 
                    e.printStackTrace(); 
                } 
            } 
        } 
    } 
  
    class LTQConsumer implements Runnable { 
        int id; 
        LTQConsumer(int id) 
        { 
            this.id = id; 
        } 
  
        @Override
        public void run() 
        { 
            try { 
                System.out.println("Consumer "
                                   + id 
                                   + " is waiting to "
                                   + "take an element."); 
                System.out.println("Is there any consumer"
                                   + " still waiting to"
                                   + " receive an element"
                                   + " after transfer -> "
                                   + LTQ.hasWaitingConsumer()); 
                Integer s = LTQ.take(); 
                System.out.println("Consumer "
                                   + id 
                                   + " received Element: "
                                   + s); 
            } 
            catch (InterruptedException e) { 
                System.out.println(e); 
            } 
        } 
    } 
  
    // Driver code 
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        GFG ob = new GFG(); 
  
        ExecutorService exService 
            = Executors.newFixedThreadPool(3); 
  
        LTQProducer p = ob.new LTQProducer(); 
        LTQConsumer c1 = ob.new LTQConsumer(0); 
        LTQConsumer c2 = ob.new LTQConsumer(1); 
  
        exService.execute(p); 
        exService.execute(c1); 
        exService.execute(c2); 
  
        exService.shutdown(); 
    } 
} 

Output:

Producer is waiting to transfer
Consumer 0 is waiting to take an element.
Is there any consumer waiting to take an element -> false
Consumer 1 is waiting to take an element.
Is there any consumer waiting to take an element -> false
Consumer 0 received Element: 0
Producer transferred element: 0
Is there any consumer still waiting to receive an element after transfer -> true
Producer is waiting to transfer
Producer transferred element: 1
Consumer 1 received Element: 1
Is there any consumer still waiting to receive an element after transfer -> false
Producer is waiting to transfer

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