/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jackrabbit.core.id;
import java.security.SecureRandom;
import java.util.Random;
/**
* Automatically seeded singleton secure random number generator.
*
* @see <a href="https://issues.apache.org/jira/browse/JCR-1206">JCR-1206</a>:
* UUID generation: SecureRandom should be used by default
*/
class SeededSecureRandom extends SecureRandom implements Runnable {
/**
* Maximum number of milliseconds to wait for the seeding.
*/
private static final int MAX_SEED_TIME = 1000;
/**
* Singleton instance of this class. Initialized when first accessed.
*/
private static volatile Random instance = null;
/**
* Returns the singleton instance of this class. The instance is
* created and seeded when this method is first called.
*
* @return seeded secure random number generator
*/
public static Random getInstance() {
if (instance == null) {
synchronized (SeededSecureRandom.class) {
if (instance == null) {
instance = new SeededSecureRandom();
}
}
}
return instance;
}
/**
* Flag to indicate whether seeding is complete.
*/
private volatile boolean seeded = false;
/**
* Creates and seeds a secure random number generator.
*/
private SeededSecureRandom() {
// Can not do that in a static initializer block, because
// threads are not started after the initializer block exits
Thread thread = new Thread(this, "SeededSecureRandom");
thread.setDaemon(true);
thread.start();
try {
thread.join(MAX_SEED_TIME);
} catch (InterruptedException e) {
// ignore
}
if (!seeded) {
// Alternative seed algorithm if the default is very slow
setSeed(System.currentTimeMillis());
setSeed(System.nanoTime());
setSeed(new Object().hashCode());
Runtime runtime = Runtime.getRuntime();
setSeed(runtime.freeMemory());
setSeed(runtime.maxMemory());
setSeed(runtime.totalMemory());
setSeed(System.getProperties().toString().hashCode());
// Thread timing (a second thread is already running)
for (int j = 0; j < 16; j++) {
int i = 0;
long start = System.currentTimeMillis();
while (start == System.currentTimeMillis()) {
i++;
}
// Supplement the existing seed
setSeed(i);
}
}
}
/**
* Seeds this random number generator with 32 bytes of random data.
* Run in an initializer thread as this may be slow on some systems, see
* http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6202721.
*/
public void run() {
setSeed(generateSeed(32));
seeded = true;
}
}