Java ReentrantLock tryLock() Method

The tryLock() method of ReentrantLock class holds the lock only when any other thread does not hold it at the time of invocation. If the current thread already holds this lock, then the hold count is incremented by one, and the method returns true. Otherwise false.

Syntax

public boolean tryLock()

public boolean tryLock(long timeout, TimeUnit unit)
                throws InterruptedException

Parameter

timeout - the time to wait for the lock

unit - the time unit of the timeout argument

Returns

true if the lock was free and was acquired by the current thread. Otherwise false.

Throws

InterruptedException - if the current thread is interrupted

NullPointerException - if the time unit is null

Example 1

 import java.text.SimpleDateFormat; 
 import java.util.Date; 
 import java.util.concurrent.ExecutorService; 
 import java.util.concurrent.Executors; 
 import java.util.concurrent.locks.ReentrantLock; 
   
 class tryLockClass implements Runnable 
 { 
   String nm; 
   ReentrantLock relc; 
   public tryLockClass(ReentrantLock rl, String n) 
   { 
     relc = rl; 
     nm = n; 
   } 
   public void run() 
   { 
     boolean dn = false; 
     while (!dn) 
     { 
       try {
    	   int c=0;
       if(relc.tryLock()) 
       { 
			int i;
			Thread t1=new Thread();
			for( i =5 ; i <= 10 ; i++)
				System.out.println(t1.getName());
				 t1.checkAccess();
			t1.countStackFrames();
			c=c+1;
			if(i>7)
			{
		System.out.println(t1.getName());
			break;
				
      }
		
      
      }
      } 
		     finally
		     { 
		       //Outer lock release 
		       System.out.println("task name - " + nm + 
		                  " releasing lock(outer lock)"); 
  
		       relc.unlock(); 
		       System.out.println("Lock Hold Count - " + 
		                    relc.getHoldCount()); 
		     } 
		   } 
		   
    } 
  } 

public class ReentrantLocktryLockExample1
 { 
   static final int MAX_Time = 2; 
   public static void main(String[] args) 
   { 
     ReentrantLock rel = new ReentrantLock(); 
     ExecutorService pool = Executors.newFixedThreadPool(MAX_Time); 
     Runnable wrk1 = new tryLockClass(rel, "Job1"); 
     pool.execute(wrk1); 
     pool.shutdown(); 
   } 
 }

Test it Now

Output:

Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
task name - Job1 releasing lock(outer lock)
Lock Hold Count - 0

Example 2

//import statements

 import java.text.SimpleDateFormat; 
 import java.util.Date; 
 import java.util.concurrent.ExecutorService; 
 import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock; 
   
 class Worker9 implements Runnable 
 { 
   String nm; 
   ReentrantLock relc; 
   public Worker9(ReentrantLock rl, String n) 
   { 
     relc = rl; 
     nm = n; 
   } 
   public void run() 
   { 
     boolean dn = false; 
     while (!dn) 
     { 
    	 TimeUnit unit = TimeUnit.valueOf("DAYS"); 
        
       try {
    	   int c=0;
		if(relc.tryLock(78653, unit)) 
		   { 
			int i;
			Thread t1=new Thread();
			for( i =5 ; i <= 10 ; i++)
				System.out.println(t1.getName());
				 t1.checkAccess();
			t1.countStackFrames();
			c=c+1;
			if(i>7)
			{
		System.out.println(t1.getName());
			break;
				
       }
		
       
       }
       }
		     catch(InterruptedException e) 
		     { 
		       e.printStackTrace(); 
		     } 
		     finally
		     { 
		       //Outer lock release 
		       System.out.println("task name - " + nm + 
		                  " releasing lock(outer lock)"); 
   
		       relc.unlock(); 
		       System.out.println("Lock Hold Count - " + 
		                    relc.getHoldCount()); 
		     } 
		   } 
		   
     } 
   } 
 
   
 public class  ReentrantLocktryLockExample2
 { 
   static final int MAX_Time = 2; 
   public static void main(String[] args) 
   { 
     ReentrantLock rel = new ReentrantLock(); 
     ExecutorService pool = Executors.newFixedThreadPool(MAX_Time); 
     Runnable wrk1 = new Worker9(rel, "Job1"); 
     Runnable wrk2 = new Worker9(rel, "Job2"); 
     pool.execute(wrk1); 
     pool.execute(wrk2); 
     pool.shutdown(); 
   } 
 }

Test it Now

Output:

Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
Thread-0
task name - Job1 releasing lock(outer lock)
Lock Hold Count - 0
Thread-1
Thread-1
Thread-1
Thread-1
Thread-1
Thread-1
Thread-1
task name - Job2 releasing lock(outer lock)
Lock Hold Count - 0

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