/*
* The MIT License
*
* Copyright (c) 2012, CloudBees, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package hudson.scheduler;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;
/**
* Generates a pseudo-random sequence of integers in the specified range.
*
* <p>
* {@link CronTab} supports tokens like '@daily', which means "do it once a day".
* Exactly which time of the day this gets scheduled is randomized --- randomized
* in the sense that it's spread out when many jobs choose @daily, but it's at
* the same time stable so that every job sticks to a specific time of the day
* even after the configuration is updated.
*
* <p>
*
*
* @author Kohsuke Kawaguchi
* @since 1.448
*/
public abstract class Hash {
/*package*/ Hash() {}
/**
* Produces an integer in [0,n)
*/
public abstract int next(int n);
public static Hash from(String seed) {
try {
MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(seed.getBytes("UTF-8"));
byte[] digest = md5.digest();
for (int i=8; i<digest.length; i++)
digest[i%8] ^= digest[i];
long l = 0;
for (int i=0; i<8; i++)
l = (l<<8)+(digest[i]&0xFF);
final Random rnd = new Random(l);
return new Hash() {
@Override
public int next(int n) {
return rnd.nextInt(n);
}
};
} catch (NoSuchAlgorithmException e) {
throw new AssertionError(e); // MD5 is a part of JRE
} catch (UnsupportedEncodingException e) {
throw new AssertionError(e); // UTF-8 is mandatory
}
}
/**
* Creates a hash that always return 0.
*/
public static Hash zero() {
return ZERO;
}
private static final Hash ZERO = new Hash() {
@Override
public int next(int n) {
return 0;
}
};
}