Java ReentrantLock getQueueLength() Method

by Online Tutorials Library July 22, 2022

Java Reentrant getQueueLength() Method

The getQueueLength() method of ReentrantLock Class returns the number of threads waiting to get the lock. The value is approximate because the number of threads can change dynamically while traversing internal data structures. It is used to monitor the state.

Syntax

Parameter

No parameter is passed.

Returns

the estimated number of threads waiting for this lock

Throws

No Exception is thrown.

Example 1

   import java.util.concurrent.locks.ReentrantLock;      public class ReentrantLockgetQueueLengthExample1  {       public static void main(String[] args) {                  ReentrantLock lock=new ReentrantLock();              MyRunnableClass90 myRnbl=new MyRunnableClass90(lock);              new Thread(myRnbl,”Thread-1″).start();                                 }   }         class MyRunnableClass90 implements Runnable{              ReentrantLock lock;       public MyRunnableClass90(ReentrantLock lock) {               this.lock=lock;       }              public void run(){              int i;              Thread t1 = new Thread();              Thread t2 = new Thread();              t1.holdsLock(t1);              t2.holdsLock(t2);       for(i=5;i<=10;i++) {       if(i==7)       {              System.out.println(” getQueueLength = “+lock.getQueueLength()+”  “);       }       if(i==5)             System.out.println(Thread.currentThread().getName()                           +” has released the lock.”);                                  }       }   }  

Test it Now

Output:

Thread-1 has released the lock.   getQueueLength = 0

Example 2

   import java.util.concurrent.locks.ReentrantLock;      public class ReentrantLockgetQueueLengthExample2 {       public static void main(String[] args) {                  ReentrantLock lock=new ReentrantLock();              MyRunnableClass10 myRnbl=new MyRunnableClass10(lock);              new Thread(myRnbl,”ThreadA”).start();              new Thread(myRnbl,”ThreadB”).start();              new Thread(myRnbl,”ThreadC”).start();                     }   }         class MyRunnableClass10 implements Runnable{              ReentrantLock lock;       public MyRunnableClass10(ReentrantLock lock) {               this.lock=lock;       }              public void run(){                                         lock.lock();                  System.out.println(Thread.currentThread().getName()                           +” has got the  lock.”);                                   try {  Thread.sleep(2000);  } catch (InterruptedException e) {  // TODO Auto-generated catch block  e.printStackTrace();  }                           System.out.println(“getQueueLength = “+lock.getQueueLength());                            lock.unlock();         }   }  

Test it Now

Output:

ThreadB has got the  lock.  getQueueLength = 2  ThreadA has got the  lock.  getQueueLength = 1  ThreadC has got the  lock.  getQueueLength = 0

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