/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.test;

import java.util.concurrent.CountDownLatch;

/**
 * Controls two threads that would otherwise race and produce non-deterministic outcome.
 * (ascii-art looks odd in source but lines up in fixed-size generated javadoc).
 * <pre>
 *          {@link Control#await() T1 await()}                   {@link Control#release() T1 release()}
 *               |                              |
 * -T1/T2--------|-T2-----------|-T1------------|-T1/T2------------------>
 *                              |
 *                        {@link #reached() T2 reached()}
 * </pre>
 */
public interface Barrier {
    void reached();

    class Control implements Barrier {
        private final CountDownLatch reached = new CountDownLatch(1);
        private final CountDownLatch released = new CountDownLatch(1);

        @Override
        public void reached() {
            try {
                reached.countDown();
                released.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }

        public void await() throws InterruptedException {
            reached.await();
        }

        public void awaitUninterruptibly() {
            boolean interrupted = false;
            try {
                while (true) {
                    try {
                        await();
                        return;
                    } catch (InterruptedException e) {
                        interrupted = true;
                    }
                }
            } finally {
                if (interrupted) {
                    Thread.currentThread().interrupt();
                }
            }
        }

        public void release() {
            released.countDown();
        }
    }
}
