BlockingAtomicReference.java

package org.jstage.shop.commons.utils;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicReference;

public class BlockingAtomicReference<V> extends AtomicReference<V> {

	private final CountDownLatch initialized = new CountDownLatch(1);

	/**
	 * Initializes this reference with a value.
	 * <p/>
	 * If there where calls to {@link #blockingGet()} from other threads, these calls will return.
	 *
	 * @param value the initial value
	 */
	public void initialize(V value) {
		set(value);
		initialized.countDown();
	}

	/**
	 * Gets the current value, waiting until this reference got initialized via the {@link #initialize} method.
	 * <p/>
	 * After {@link #initialize} was called, this method behaves just like {@link #get}
	 *
	 * @return the current value
	 */
	public V blockingGet() throws InterruptedException {
		initialized.await();
		return get();
	}
}

BlockingAtomicReferenceTest.java

package org.jstage.shop.commons.utils;

import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class BlockingAtomicReferenceTest {

	@Test
	public void testBlockingGet() throws Exception {
		final BlockingAtomicReference<Boolean> ref = new BlockingAtomicReference<>();
		new Thread(() -> ref.initialize(true)).start();
		assertTrue(ref.blockingGet());
	}
}