com.netflix.zeno.fastblob.state.FreeOrdinalTracker Maven / Gradle / Ivy

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/*
 *
 *  Copyright 2013 Netflix, Inc.
 *
 *     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.netflix.zeno.fastblob.state;

import com.netflix.zeno.fastblob.record.VarInt;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;

/**
 * A stack of unused ordinals.
 *
 * This helps fill the "holes" generated by removing unused ordinals during server processing.
 *
 * @author dkoszewnik
 *
 */
public class FreeOrdinalTracker {

    private int freeOrdinals[];
    private int size;
    private int nextEmptyOrdinal;

    public FreeOrdinalTracker() {
        this(0);
    }

    private FreeOrdinalTracker(int nextEmptyOrdinal) {
        this.freeOrdinals = new int[64];
        this.nextEmptyOrdinal = nextEmptyOrdinal;
        this.size = 0;
    }

    /**
     * @return either an ordinal which was previously deallocated, or the next empty, previously unallocated ordinal in the sequence 0-n
     */
    public int getFreeOrdinal() {
        if(size == 0)
            return nextEmptyOrdinal++;

        return freeOrdinals[--size];
    }

    /**
     * Return an ordinal to the pool after the object to which it was assigned is discarded.
     *
     * @param ordinal
     */
    public void returnOrdinalToPool(int ordinal) {
        if(size == freeOrdinals.length) {
            freeOrdinals = Arrays.copyOf(freeOrdinals, freeOrdinals.length * 3 / 2);
        }

        freeOrdinals[size] = ordinal;
        size++;
    }


    public void serializeTo(OutputStream os) throws IOException {
        VarInt.writeVInt(os, nextEmptyOrdinal);
        VarInt.writeVInt(os, size);

        for(int i=0;i