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//: concurrency/AttemptLocking.java

// Locks in the concurrent library allow you

// to give up on trying to acquire a lock.

import java.util.concurrent.*;

import java.util.concurrent.locks.*;

public class AttemptLocking {

private ReentrantLock lock = new ReentrantLock();

public void untimed() {

boolean captured = lock.tryLock();

try {

System.out.println("tryLock(): " + captured);

} finally {

if(captured)

lock.unlock();

}

}

public void timed() {

boolean captured = false;

try {

captured = lock.tryLock(2, TimeUnit.SECONDS);

} catch(InterruptedException e) {

throw new RuntimeException(e);

}

try {

System.out.println("tryLock(2, TimeUnit.SECONDS): " +

captured);

} finally {

if(captured)

lock.unlock();

}

}

public static void main(String[] args) {

final AttemptLocking al = new AttemptLocking();

al.untimed(); // True -- lock is available

al.timed(); // True -- lock is available

// Now create a separate task to grab the lock:

new Thread() {

{ setDaemon(true); }

public void run() {

al.lock.lock();

System.out.println("acquired");

}

}.start();

Thread.yield(); // Give the 2nd task a chance

al.untimed(); // False -- lock grabbed by task

al.timed(); // False -- lock grabbed by task

}

} /* Output:

tryLock(): true

tryLock(2, TimeUnit.SECONDS): true

acquired

tryLock(): false

tryLock(2, TimeUnit.SECONDS): false

*///:~