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 *  Copyright (c) 2014-2019 Appsicle
 *  Copyright (c) 2019-2022 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,
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package io.questdb.mp;

import io.questdb.std.*;

import java.io.Closeable;

public class RingQueue implements Closeable {
    private final int mask;
    private final T[] buf;
    private final long memory;
    private long memorySize;
    private final int memoryTag;

    @SuppressWarnings("unchecked")
    public RingQueue(ObjectFactory factory, int cycle) {

        // zero queue is allowed for testing
        assert cycle == 0 || Numbers.isPow2(cycle);

        this.mask = cycle - 1;
        this.buf = (T[]) new Object[cycle];

        for (int i = 0; i < cycle; i++) {
            buf[i] = factory.newInstance();
        }

        // heap based queue
        this.memory = 0;
        this.memorySize = 0;
        this.memoryTag = 0;
    }

    @SuppressWarnings("unchecked")
    public RingQueue(DirectObjectFactory factory, long slotSize, int cycle, int memoryTag) {
        this.mask = cycle - 1;
        this.buf = (T[]) new Object[cycle];

        this.memorySize = slotSize * cycle;
        this.memoryTag = memoryTag;
        this.memory = Unsafe.calloc(memorySize, memoryTag);
        long p = memory;
        for (int i = 0; i < cycle; i++) {
            // intention is that whatever comes out of the factory it should work with the
            // memory allocated by the queue for this slot and should not reallocate ever
            buf[i] = factory.newInstance(p, slotSize);
            p += slotSize;
        }
    }

    @Override
    public void close() {
        for (int i = 0, n = buf.length; i < n; i++) {
            Misc.free(buf[i]);
        }
        if (memorySize > 0) {
            Unsafe.free(memory, memorySize, memoryTag);
            this.memorySize = 0;
        }
    }

    public T get(long cursor) {
        return buf[(int) (cursor & mask)];
    }

    public int getCycle() {
        return buf.length;
    }
}