/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Written by Doug Lea with assistance from members of JCP JSR-166

 * Expert Group and released to the public domain, as explained at

 * http://creativecommons.org/publicdomain/zero/1.0/

 */

/*

 * @test

 * @bug 4949279 6937857

 * @summary Independent instantiations of Random() have distinct seeds.

 */

import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Random;

public class DistinctSeeds {

    public static void main(String[] args) throws Exception {

        // Strictly speaking, it is possible for these to randomly fail,

        // but the probability should be small (approximately 2**-48).

        if (new Random().nextLong() == new Random().nextLong() ||

            new Random().nextLong() == new Random().nextLong())

            throw new RuntimeException("Random() seeds not unique.");

        // Now try generating seeds concurrently

        class RandomCollector implements Runnable {

            long[] randoms = new long[1<<17];

            public void run() {

                for (int i = 0; i < randoms.length; i++)

                    randoms[i] = new Random().nextLong();

            }

        }

        final int threadCount = 2;

        List<RandomCollector> collectors = new ArrayList<>();

        List<Thread> threads = new ArrayList<Thread>();

        for (int i = 0; i < threadCount; i++) {

            RandomCollector r = new RandomCollector();

            collectors.add(r);

            threads.add(new Thread(r));

        }

        for (Thread thread : threads)

            thread.start();

        for (Thread thread : threads)

            thread.join();

        int collisions = 0;

        HashSet<Long> s = new HashSet<Long>();

        for (RandomCollector r : collectors) {

            for (long x : r.randoms) {

                if (s.contains(x))

                    collisions++;

                s.add(x);

            }

        }

        System.out.printf("collisions=%d%n", collisions);

        if (collisions > 10)

            throw new Error("too many collisions");

    }

}