ConcurrentInitializeTest.java

package aQute.lib.concurrentinit;

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

import org.junit.Assert;
import org.junit.Test;

public class ConcurrentInitializeTest extends Assert {
	final static Executor executor = Executors.newCachedThreadPool();

	@Test
	public void testSimple() throws Exception {
		ConcurrentInitialize<String> ci = new ConcurrentInitialize<String>() {

			@Override
			public String create() throws Exception {
				return "foo";
			}
		};
		assertEquals("foo", ci.get());
	}

	@Test
	public void testConcurrent() throws InterruptedException {
		final Semaphore result = new Semaphore(0);
		final Semaphore onCreate = new Semaphore(0);
		final ConcurrentInitialize<String> ci = new ConcurrentInitialize<String>() {

			@Override
			public String create() throws Exception {
				onCreate.acquire();
				return "foo";
			}
		};
		final Thread threads [] = new Thread[10];

		for (int i = 0; i < 10; i++) {
			final int j = i;
			executor.execute(new Runnable() {
				@Override
				public void run() {
					threads[j] = Thread.currentThread();

					try {
						ci.get();
						result.release();
					} catch (Exception e) {
						// cant happen
					}
				}
			});
		}
		// First wait so that we can verify that nobody can
		// continue until we allow it
		Thread.sleep(100);
		assertEquals(0, result.availablePermits());

		// allow the creator to pass
		onCreate.release(1); // only 1 can create

		// Check the results
		result.acquire(10);
	}

	@Test(expected = Exception.class)
	public void testExceptionForFirstCall() throws Exception {
		ConcurrentInitialize<String> ci = new ConcurrentInitialize<String>() {

			@Override
			public String create() throws Exception {
				throw new Exception();
			}
		};
		ci.get();
	}

	@Test(expected = Exception.class)
	public void testExceptionForFurtherCalls() throws Exception {
		ConcurrentInitialize<String> ci = new ConcurrentInitialize<String>() {

			@Override
			public String create() throws Exception {
				throw new Exception();
			}
		};
		try {
			ci.get();
		} catch (Exception e) {
			// ignore
		}
		ci.get();
	}

}