88 lines
3.2 KiB
Java
88 lines
3.2 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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/*
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* @test
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* @bug 4949279 6937857
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* @summary Independent instantiations of Random() have distinct seeds.
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* @key randomness
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*/
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Random;
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public class DistinctSeeds {
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public static void main(String[] args) throws Exception {
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// Strictly speaking, it is possible for these to randomly fail,
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// but the probability should be small (approximately 2**-48).
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if (new Random().nextLong() == new Random().nextLong() ||
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new Random().nextLong() == new Random().nextLong())
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throw new RuntimeException("Random() seeds not unique.");
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// Now try generating seeds concurrently
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class RandomCollector implements Runnable {
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long[] randoms = new long[1<<17];
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public void run() {
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for (int i = 0; i < randoms.length; i++)
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randoms[i] = new Random().nextLong();
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}
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}
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final int threadCount = 2;
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List<RandomCollector> collectors = new ArrayList<>();
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List<Thread> threads = new ArrayList<>();
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for (int i = 0; i < threadCount; i++) {
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RandomCollector r = new RandomCollector();
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collectors.add(r);
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threads.add(new Thread(r));
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}
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for (Thread thread : threads)
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thread.start();
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for (Thread thread : threads)
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thread.join();
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int collisions = 0;
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HashSet<Long> s = new HashSet<>();
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for (RandomCollector r : collectors) {
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for (long x : r.randoms) {
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if (s.contains(x))
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collisions++;
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s.add(x);
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}
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}
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System.out.printf("collisions=%d%n", collisions);
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if (collisions > 10)
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throw new Error("too many collisions");
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}
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}
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