Touring Additional Utility APIs - Beginning Java 7 - page 557

servedword)istheirabilitytobackoutofanattempttoacquirealock.Forexample,
the tryLock() methodbacksoutwhenthelockisnotavailableimmediatelyorwhen
a timeout expires (if specified). Also, the lockInterruptibly() method backs
out when another thread sends an interrupt before the lock is acquired.

ReentrantLock implements Lock ,describingareentrantmutualexclusion Lock
implementationwiththesamebasicbehaviorandsemanticsastheimplicitmonitorlock
accessed via synchronized , but with extended capabilities.
Listing 6-4 demonstrates Lock and ReentrantLock in a version of Listing 6-3
thatensuresthattheoutputisnevershowninincorrectorder(aconsumedmessageap-
pearing before a produced message).

Listing 6-4. Achieving synchronization in terms of locks

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class PC
{

public static void main(String[] args)
{

final Lock lock = new ReentrantLock();
final BlockingQueue<Character> bq;
bq = new ArrayBlockingQueue<Character>(26);
final ExecutorService executor = Execut-

ors.newFixedThreadPool(2);
Runnable producer;
producer = new Runnable()
{

public void run()
{

for (char ch = 'a'; ch <= 'z'; ch++)