DistinctSeeds.java revision 3984
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0N/A * under the terms of the GNU General Public License version 2 only, as
0N/A * published by the Free Software Foundation.
0N/A *
0N/A * This code is distributed in the hope that it will be useful, but WITHOUT
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0N/A * version 2 for more details (a copy is included in the LICENSE file that
0N/A * accompanied this code).
0N/A *
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0N/A
0N/A/*
0N/A * This file is available under and governed by the GNU General Public
0N/A * License version 2 only, as published by the Free Software Foundation.
0N/A * However, the following notice accompanied the original version of this
0N/A * file:
0N/A *
0N/A * Written by Doug Lea with assistance from members of JCP JSR-166
0N/A * Expert Group and released to the public domain, as explained at
0N/A * http://creativecommons.org/publicdomain/zero/1.0/
0N/A */
0N/A
0N/A/*
0N/A * @test
0N/A * @bug 4949279 6937857
0N/A * @summary Independent instantiations of Random() have distinct seeds.
0N/A */
0N/A
0N/Aimport java.util.ArrayList;
0N/Aimport java.util.HashSet;
0N/Aimport java.util.List;
0N/Aimport java.util.Random;
0N/A
0N/Apublic class DistinctSeeds {
0N/A public static void main(String[] args) throws Exception {
0N/A // Strictly speaking, it is possible for these to randomly fail,
0N/A // but the probability should be small (approximately 2**-48).
0N/A if (new Random().nextLong() == new Random().nextLong() ||
0N/A new Random().nextLong() == new Random().nextLong())
0N/A throw new RuntimeException("Random() seeds not unique.");
0N/A
0N/A // Now try generating seeds concurrently
0N/A class RandomCollector implements Runnable {
0N/A long[] randoms = new long[1<<17];
0N/A public void run() {
0N/A for (int i = 0; i < randoms.length; i++)
0N/A randoms[i] = new Random().nextLong();
0N/A }
0N/A }
0N/A final int threadCount = 2;
0N/A List<RandomCollector> collectors = new ArrayList<>();
0N/A List<Thread> threads = new ArrayList<Thread>();
0N/A for (int i = 0; i < threadCount; i++) {
0N/A RandomCollector r = new RandomCollector();
0N/A collectors.add(r);
0N/A threads.add(new Thread(r));
0N/A }
0N/A for (Thread thread : threads)
0N/A thread.start();
0N/A for (Thread thread : threads)
0N/A thread.join();
0N/A int collisions = 0;
0N/A HashSet<Long> s = new HashSet<Long>();
0N/A for (RandomCollector r : collectors) {
0N/A for (long x : r.randoms) {
0N/A if (s.contains(x))
0N/A collisions++;
0N/A s.add(x);
0N/A }
0N/A }
0N/A System.out.printf("collisions=%d%n", collisions);
0N/A if (collisions > 10)
0N/A throw new Error("too many collisions");
0N/A }
0N/A}
0N/A