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 *
 *  Copyright (c) 2014-2019 Appsicle
 *  Copyright (c) 2019-2020 QuestDB
 *
 *  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.
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package io.questdb.std;

import io.questdb.log.Log;
import io.questdb.log.LogFactory;
import org.jetbrains.annotations.NotNull;

/**
 * Single threaded object pool based on ObjList. The goal is to optimise intermediate allocation of intermediate objects.
 */
public class ObjectPool implements Mutable {

    private final static Log LOG = LogFactory.getLog(ObjectPool.class);
    private final ObjList list;
    private final ObjectFactory factory;
    private int pos = 0;
    private int size;

    public ObjectPool(@NotNull ObjectFactory factory, int size) {
        this.list = new ObjList<>(size);
        this.factory = factory;
        this.size = size;
        fill();
    }

    @Override
    public void clear() {
        pos = 0;
    }

    public T next() {
        if (pos == size) {
            expand();
        }

        T o = list.getQuick(pos++);
        o.clear();
        return o;
    }

    private void expand() {
        fill();
        size <<= 1;
        LOG.info().$("pool resize [class=").$(factory.getClass().getName()).$(", size=").$(size).$(']').$();
    }

    private void fill() {
        for (int i = 0; i < size; i++) {
            list.add(factory.newInstance());
        }
    }
}