LocklessRingBuffer.h

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/*
 * LocklessRingBuffer.h - LMMS wrapper for a lockless ringbuffer library
 *
 * Copyright (c) 2019 Martin Pavelek <he29/dot/HS/at/gmail/dot/com>
 *
 * This file is part of LMMS - https://lmms.io
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program (see COPYING); if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301 USA.
 *
 */
 
#ifndef LMMS_LOCKLESS_RING_BUFFER_H
#define LMMS_LOCKLESS_RING_BUFFER_H
 
#include <QMutex>
#include <QWaitCondition>
 
#include <ringbuffer/ringbuffer.h>
 
#include "LmmsTypes.h"
 
namespace lmms
{

template <class T>
class LocklessRingBuffer
{
    template<class _T>
    friend class LocklessRingBufferReader;
public:
    LocklessRingBuffer(std::size_t sz) : m_buffer(sz)
    {
        m_buffer.touch();   // reserve storage space before realtime operation starts
    }
    ~LocklessRingBuffer() = default;
 
    std::size_t capacity() const {return m_buffer.maximum_eventual_write_space();}
    std::size_t free() const {return m_buffer.write_space();}
    void wakeAll() {m_notifier.wakeAll();}
    std::size_t write(const T *src, std::size_t cnt, bool notify = false)
    {
        std::size_t written = LocklessRingBuffer<T>::m_buffer.write(src, cnt);
        // Let all waiting readers know new data are available.
        if (notify) {LocklessRingBuffer<T>::m_notifier.wakeAll();}
        return written;
    }
    void mlock() { m_buffer.mlock(); }
 
protected:
    ringbuffer_t<T> m_buffer;
    QWaitCondition m_notifier;
};
 

template <class T>
class LocklessRingBufferReader : public ringbuffer_reader_t<T>
{
public:
    LocklessRingBufferReader(LocklessRingBuffer<T> &rb) :
        ringbuffer_reader_t<T>(rb.m_buffer),
        m_notifier(&rb.m_notifier) {};
 
    bool empty() const {return !this->read_space();}
    void waitForData()
    {
        QMutex useless_lock;
        useless_lock.lock();
        m_notifier->wait(&useless_lock);
        useless_lock.unlock();
    }
private:
    QWaitCondition *m_notifier;
};
 
 
} // namespace lmms
 
#endif // LMMS_LOCKLESS_RING_BUFFER_H