kis_lock_free_lod_counter.h

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/*
 *  SPDX-FileCopyrightText: 2014 Dmitry Kazakov <dimula73@gmail.com>
 *
 *  SPDX-License-Identifier: GPL-2.0-or-later
 */
 
#ifndef __KIS_LOCK_FREE_LOD_COUNTER_H
#define __KIS_LOCK_FREE_LOD_COUNTER_H
 
#include <QAtomicInt>
 
 
class KisLockFreeLodCounter
{
public:
    void addLod(int newLod) {
        int oldValue = 0;
        int newValue = 0;
 
        do {
            oldValue = m_num;
 
            int counter;
            int lod;
            unpackLod(oldValue, &counter, &lod);
 
            if (!counter) {
                lod = newLod;
            } else {
                Q_ASSERT(lod == newLod);
            }
 
            counter++;
            newValue = packLod(counter, lod);
        } while(!m_num.testAndSetOrdered(oldValue, newValue));
    }
 
    void removeLod() {
        int oldValue = 0;
        int newValue = 0;
 
        do {
            oldValue = m_num;
 
            int counter;
            int lod;
            unpackLod(oldValue, &counter, &lod);
 
            Q_ASSERT(counter > 0);
 
            counter--;
            newValue = packLod(counter, lod);
        } while(!m_num.testAndSetOrdered(oldValue, newValue));
    }
 
    int readLod() const {
        int value = m_num;
 
        int counter;
        int lod;
        unpackLod(value, &counter, &lod);
 
        return counter ? lod : -1;
    }
 
    void testingClear() {
        m_num = 0;
    }
 
private:
    static inline int packLod(int counter, int lod) {
        return (counter << 8) | (lod & 0xFF);
    }
 
    static inline void unpackLod(int value, int *counter, int *lod) {
        *lod = value & 0xFF;
        *counter = value >> 8;
    }
 
private:
    QAtomicInt m_num;
};
 
#endif /* __KIS_LOCK_FREE_LOD_COUNTER_H */