com.gs.fw.common.mithra.util.MithraCompositeListQueue Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of reladomo Show documentation

Reladomo is an object-relational mapping framework.

There is a newer version: 18.1.0

/*
 Copyright 2016 Goldman Sachs.
 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.gs.fw.common.mithra.util;


import com.gs.collections.impl.list.mutable.FastList;

import java.util.List;
import java.util.concurrent.atomic.AtomicIntegerArray;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

public class MithraCompositeListQueue extends ListBasedQueue
{
    private static final AtomicIntegerFieldUpdater currentIndexUpdater = AtomicIntegerFieldUpdater.newUpdater(MithraCompositeListQueue.class, "current");

    private final FastList lists;
    private final AtomicIntegerArray countArray;
    private final int chunkSize;
    private volatile int current = 0;

    public MithraCompositeListQueue(MithraCompositeList compositeList, int chunkSize)
    {
        this.lists = compositeList.getLists();
        this.countArray = new AtomicIntegerArray(lists.size());
        this.chunkSize = chunkSize;
    }

    public List borrow(List existing)
    {
        ResettableSubList existingSubList = (ResettableSubList) existing;
        if (existingSubList == null)
        {
            existingSubList = new ResettableSubList();
        }
        while(true)
        {
            int cur = current;
            if (cur < countArray.length()) // due to the concurrency on "current", this if statement can't be pulled out into the while clause
            {
                List target = lists.get(cur);
                int end = countArray.addAndGet(cur, chunkSize);
                int start = end - chunkSize;
                int targetSize = target.size();
                if (start < targetSize)
                {
                    if (end > targetSize)
                    {
                        end = targetSize;
                    }
                    existingSubList.reset(target, start, end - start);
                    return existingSubList;
                }
                currentIndexUpdater.compareAndSet(this, cur, cur + 1);
            }
            else break;
        }
        return null;
    }



}