/**
* 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.waveprotocol.box.webclient.search;
import com.google.common.annotations.VisibleForTesting;
import org.waveprotocol.wave.client.scheduler.Scheduler.IncrementalTask;
import org.waveprotocol.wave.client.scheduler.SchedulerInstance;
import org.waveprotocol.wave.client.scheduler.TimerService;
import org.waveprotocol.wave.model.util.CollectionUtils;
import java.util.Queue;
/**
* An item pool that attempts to ensure that its free pool always has a minimum
* number of items.
*
* @author hearnden@google.com (David Hearnden)
*/
public final class ToppingUpPool<T> implements Pool<T>, IncrementalTask {
/**
* Item factory.
*/
public interface Factory<T> {
T create();
}
/** Timer for running the top-up task. */
private final TimerService timer;
/** Desired number of items to be ready in the free pool. */
private final int minimumFreeCount;
/** Store of freed items. */
private final Queue<T> free = CollectionUtils.createQueue();
/** Object factory. */
private final Factory<? extends T> factory;
/** Number of items created. */
private int created;
@VisibleForTesting
ToppingUpPool(TimerService timer, Factory<? extends T> factory, int minimumFreeCount) {
this.timer = timer;
this.factory = factory;
this.minimumFreeCount = minimumFreeCount;
warmUpLater();
}
/**
* Creates a pool.
*
* @param factory factory for creating items
* @param minSize number of items to keep free in the pool
*/
public static <T> ToppingUpPool<T> create(Factory<? extends T> factory, int minSize) {
return new ToppingUpPool<T>(SchedulerInstance.getLowPriorityTimer(), factory, minSize);
}
/**
* @return a fresh, new, item.
*/
private T summon() {
created++;
return factory.create();
}
@Override
public T get() {
T item;
if (free.isEmpty()) {
item = summon();
} else {
item = free.poll();
// If the free pool just became empty, schedule top-up.
if (free.isEmpty()) {
warmUpLater();
}
}
return item;
}
@Override
public void recycle(T itemUi) {
free.add(itemUi);
}
/**
* @return the number of items produced by this pool that are still in use
* (i.e., have not been recycled).
*/
public int getWildCount() {
return created - free.size();
}
//
// Task that, when triggered, ensures the free pool has a minimum size.
//
/**
* Warms up the item pool at some time in the future.
*/
private void warmUpLater() {
if (!timer.isScheduled(this)) {
timer.schedule(this);
}
}
@Override
public boolean execute() {
if (free.size() < minimumFreeCount) {
free.add(summon());
}
// Keep running while still more items to create
return free.size() < minimumFreeCount;
}
}