com.hazelcast.flakeidgen.impl.AutoBatcher Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2018, Hazelcast, Inc. All Rights Reserved.
*
* Licensed 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 com.hazelcast.flakeidgen.impl;
import com.hazelcast.util.Clock;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
/**
* A utility to serve IDs from IdBatch one by one, watching for validity.
* It's a separate class due to testability.
*/
public class AutoBatcher {
private final int batchSize;
private final long validity;
private volatile Block block = new Block(new IdBatch(0, 0, 0), 0);
private final IdBatchSupplier batchIdSupplier;
public AutoBatcher(int batchSize, long validity, IdBatchSupplier idGenerator) {
this.batchSize = batchSize;
this.validity = validity;
this.batchIdSupplier = idGenerator;
}
/**
* Return next ID from current batch or get new batch from supplier if
* current batch is spent or expired.
*/
public long newId() {
for (; ; ) {
Block block = this.block;
long res = block.next();
if (res != Long.MIN_VALUE) {
return res;
}
synchronized (this) {
if (block != this.block) {
// new block was assigned in the meantime
continue;
}
this.block = new Block(batchIdSupplier.newIdBatch(batchSize), validity);
}
}
}
private static final class Block {
private static final AtomicIntegerFieldUpdater NUM_RETURNED = AtomicIntegerFieldUpdater
.newUpdater(Block.class, "numReturned");
private final IdBatch idBatch;
private final long invalidSince;
private volatile int numReturned;
private Block(IdBatch idBatch, long validity) {
this.idBatch = idBatch;
this.invalidSince = validity > 0 ? Clock.currentTimeMillis() + validity : Long.MAX_VALUE;
}
/**
* Returns next ID or Long.MIN_VALUE, if there is none.
*/
long next() {
if (invalidSince <= Clock.currentTimeMillis()) {
return Long.MIN_VALUE;
}
int index;
do {
index = numReturned;
if (index == idBatch.batchSize()) {
return Long.MIN_VALUE;
}
} while (!NUM_RETURNED.compareAndSet(this, index, index + 1));
return idBatch.base() + index * idBatch.increment();
}
}
public interface IdBatchSupplier {
IdBatch newIdBatch(int batchSize);
}
}