/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.util;

import org.junit.Test;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeoutException;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

public class AtomicDisposableReferenceCounterTest {

	@Test
	public void testSerialIncrementAndDecrement() {
		AtomicDisposableReferenceCounter counter = new AtomicDisposableReferenceCounter();

		assertTrue(counter.increment());

		assertTrue(counter.decrement());

		assertFalse(counter.increment());

		assertFalse(counter.decrement());
	}

	@Test
	public void testSerialIncrementAndDecrementWithCustomDisposeCount() {
		AtomicDisposableReferenceCounter counter = new AtomicDisposableReferenceCounter(-2);

		assertTrue(counter.increment());

		assertFalse(counter.decrement());

		assertFalse(counter.decrement());

		assertTrue(counter.decrement());
	}

	@Test
	public void testConcurrentIncrementAndDecrement() throws InterruptedException, ExecutionException, TimeoutException {
		final Random random = new Random();

		final ExecutorService executor = Executors.newFixedThreadPool(2);

		try {
			final MockIncrementer incrementer = new MockIncrementer();

			final MockDecrementer decrementer = new MockDecrementer();

			// Repeat this to provoke races
			for (int i = 0; i < 256; i++) {
				final AtomicDisposableReferenceCounter counter = new AtomicDisposableReferenceCounter();
				incrementer.setCounter(counter);
				decrementer.setCounter(counter);

				counter.increment();

				// Randomly decide which one should be first as the first task usually will win the race
				boolean incrementFirst = random.nextBoolean();

				Future<Boolean> success1 = executor.submit(incrementFirst ? incrementer : decrementer);
				Future<Boolean> success2 = executor.submit(incrementFirst ? decrementer : incrementer);

				// Only one of the two should win the race and return true
				assertTrue(success1.get() ^ success2.get());
			}
		}
		finally {
			executor.shutdownNow();
		}
	}

	private static class MockIncrementer implements Callable<Boolean> {

		private AtomicDisposableReferenceCounter counter;

		void setCounter(AtomicDisposableReferenceCounter counter) {
			this.counter = counter;
		}

		@Override
		public Boolean call() throws Exception {
			return counter.increment();
		}
	}

	private static class MockDecrementer implements Callable<Boolean> {

		private AtomicDisposableReferenceCounter counter;

		void setCounter(AtomicDisposableReferenceCounter counter) {
			this.counter = counter;
		}

		@Override
		public Boolean call() throws Exception {
			return counter.decrement();
		}
	}
}