Java Reentrantlock getQueuedThreads()Method

The getQueuedThreads() returns a collection containing threads that may be waiting to acquire this lock. Because the actual threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate.

Syntax

Parameter

No parameter is passed.

Returns

the collection of threads

Throws

No Exception is thrown.

Example 1

package com.app.Rentrant;
 
  import java.util.concurrent.locks.ReentrantLock;
  
  public class ReentrantLockgetQueuedThreadExample1 {
      public static void main(String[] args) {
   
             ReentrantLock lock=new ReentrantLock();
             MyRunnableClass myRnbl=new MyRunnableClass(lock);
             new Thread(myRnbl,"Thread-1").start();
                         
      }
  }
     
  class MyRunnableClass implements Runnable{
      
      ReentrantLock lock;
      public MyRunnableClass(ReentrantLock lock) { 
             this.lock=lock;
      }
      
      public void run(){
             
             System.out.println(Thread.currentThread().getName()
                          +" is Waiting to get the lock");
             
             lock.lock();
   
             System.out.println(Thread.currentThread().getName()
                          +" has got the  lock.");
             
             try {
                    Thread.sleep(2000);
             } catch (InterruptedException e) {
                    e.printStackTrace();
             }
   
   
             System.out.println(" getQueueLength = "+lock.getQueueLength()+"  ");
             
             System.out.println(Thread.currentThread().getName()
                          +" has released the lock.");
             
             lock.unlock();    
      }
  }

Test it Now

Output:

Thread-1 is Waiting to get the lock
Thread-1 has got the lock.
 getQueueLength = 0  
Thread-1 has released the lock.

Example 2

package com.app.Rentrant;
 
  import java.util.concurrent.locks.ReentrantLock;
  
  public class ReentrantLockgetQueuedThreadExample2 {
      public static void main(String[] args) {
   
             ReentrantLock lock=new ReentrantLock();
             MyRunnableClass1 myRnbl=new MyRunnableClass1(lock);
             new Thread(myRnbl,"Thread-1").start();
             new Thread(myRnbl,"Thread-2").start();
             new Thread(myRnbl,"Thread-3").start();
             
      }
  }
    
   class MyRunnableClass1 implements Runnable{
      
      ReentrantLock lock;
      public MyRunnableClass1(ReentrantLock lock) { 
             this.lock=lock;
      }
      
      public void run(){
             
             System.out.println(Thread.currentThread().getName()
                          +" is Waiting to get the lock");
             
             lock.lock();
   
             System.out.println(Thread.currentThread().getName()
                          +" has got the  lock.");
             
             try {
                    Thread.sleep(2000);
             } catch (InterruptedException e) {
                    e.printStackTrace();
             }
   
   
             System.out.println("getQueueLength = "+lock.getQueueLength());
             
             System.out.println(Thread.currentThread().getName()
                          +" has released  the lock.");
             
             lock.unlock();    //read explanation for 5sec
      }
  }

Test it Now

Output:

Thread-1 is Waiting to get the lock
Thread-3 is Waiting to get the lock
Thread-1 has got the lock.
Thread-2 is Waiting to get the lock
getQueueLength = 2
Thread-1 has released the lock.
Thread-3 has got the lock.
getQueueLength = 1
Thread-3 has released the lock.
Thread-2 has got the lock.
getQueueLength = 0
Thread-2 has released the lock.

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