| /* |
| * 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/licenses/publicdomain |
| */ |
| |
| /* |
| * @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<RandomCollector>(); |
| 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"); |
| } |
| } |