/*
*
* Copyright (c) 2013 - 2017 Lijun Liao
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License version 3
* as published by the Free Software Foundation with the addition of the
* following permission added to Section 15 as permitted in Section 7(a):
*
* FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
* THE AUTHOR LIJUN LIAO. LIJUN LIAO DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
* OF THIRD PARTY RIGHTS.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* The interactive user interfaces in modified source and object code versions
* of this program must display Appropriate Legal Notices, as required under
* Section 5 of the GNU Affero General Public License.
*
* You can be released from the requirements of the license by purchasing
* a commercial license. Buying such a license is mandatory as soon as you
* develop commercial activities involving the XiPKI software without
* disclosing the source code of your own applications.
*
* For more information, please contact Lijun Liao at this
* address: lijun.liao@gmail.com
*/
package org.xipki.pki.ca.server.impl;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.IntBinaryOperator;
import org.xipki.commons.common.util.ParamUtil;
/**
* Idea: http://instagram-engineering.tumblr.com/post/10853187575/sharding-ids-at-instagram
* <br/>
* id consists of
* <ol>
* <li>highest bit is set to 0 to assure positive long.
* <li>epoch in ms: 46 bits for 1312 years after the epoch</li>
* <li>offset: 10 bits
* <li>shard_id: 7 bits
* </ol>
*
* @author Lijun Liao
* @since 2.0.0
*
*/
public class UniqueIdGenerator {
private static class OffsetIncrement implements IntBinaryOperator {
@Override
public int applyAsInt(int left, int right) {
return (left >= right) ? 0 : left + 1;
}
}
// maximal 10 bits
private static final int MAX_OFFSET = 0x3FF;
private final long epoch; // in milliseconds
private final int shardId; // 7 bits
private final AtomicInteger offset = new AtomicInteger(0);
private final IntBinaryOperator accumulatorFunction;
public UniqueIdGenerator(final long epoch, final int shardId) {
this.epoch = ParamUtil.requireMin("epoch", epoch, 0);
this.shardId = ParamUtil.requireRange("shardId", shardId, 0, 127);
this.accumulatorFunction = new OffsetIncrement();
}
public long nextId() {
long now = System.currentTimeMillis();
long ret = now - epoch;
ret <<= 10;
ret += offset.getAndAccumulate(MAX_OFFSET, accumulatorFunction);
ret <<= 7;
ret += shardId;
return ret;
}
}