openal-soft/alc/ringbuffer.h

#ifndef RINGBUFFER_H
#define RINGBUFFER_H

#include <stddef.h>

#include <atomic>
#include <memory>
#include <utility>

#include "albyte.h"
#include "almalloc.h"


/* NOTE: This lockless ringbuffer implementation is copied from JACK, extended
 * to include an element size. Consequently, parameters and return values for a
 * size or count is in 'elements', not bytes. Additionally, it only supports
 * single-consumer/single-provider operation.
 */

struct ll_ringbuffer_data {
    al::byte *buf;
    size_t len;
};
using ll_ringbuffer_data_pair = std::pair<ll_ringbuffer_data,ll_ringbuffer_data>;


struct RingBuffer {
    std::atomic<size_t> mWritePtr{0u};
    std::atomic<size_t> mReadPtr{0u};
    size_t mWriteSize{0u};
    size_t mSizeMask{0u};
    size_t mElemSize{0u};

    al::FlexArray<al::byte, 16> mBuffer;

    RingBuffer(const size_t count) : mBuffer{count} { }

    /** Reset the read and write pointers to zero. This is not thread safe. */
    void reset() noexcept;

    /**
     * The non-copying data reader. Returns two ringbuffer data pointers that
     * hold the current readable data. If the readable data is in one segment
     * the second segment has zero length.
     */
    ll_ringbuffer_data_pair getReadVector() const noexcept;
    /**
     * The non-copying data writer. Returns two ringbuffer data pointers that
     * hold the current writeable data. If the writeable data is in one segment
     * the second segment has zero length.
     */
    ll_ringbuffer_data_pair getWriteVector() const noexcept;

    /**
     * Return the number of elements available for reading. This is the number
     * of elements in front of the read pointer and behind the write pointer.
     */
    size_t readSpace() const noexcept;
    /**
     * The copying data reader. Copy at most `cnt' elements into `dest'.
     * Returns the actual number of elements copied.
     */
    size_t read(void *dest, size_t cnt) noexcept;
    /**
     * The copying data reader w/o read pointer advance. Copy at most `cnt'
     * elements into `dest'. Returns the actual number of elements copied.
     */
    size_t peek(void *dest, size_t cnt) const noexcept;
    /** Advance the read pointer `cnt' places. */
    void readAdvance(size_t cnt) noexcept;

    /**
     * Return the number of elements available for writing. This is the number
     * of elements in front of the write pointer and behind the read pointer.
     */
    size_t writeSpace() const noexcept;
    /**
     * The copying data writer. Copy at most `cnt' elements from `src'. Returns
     * the actual number of elements copied.
     */
    size_t write(const void *src, size_t cnt) noexcept;
    /** Advance the write pointer `cnt' places. */
    void writeAdvance(size_t cnt) noexcept;

    DEF_FAM_NEWDEL(RingBuffer, mBuffer)
};
using RingBufferPtr = std::unique_ptr<RingBuffer>;


/**
 * Create a new ringbuffer to hold at least `sz' elements of `elem_sz' bytes.
 * The number of elements is rounded up to the next power of two (even if it is
 * already a power of two, to ensure the requested amount can be written).
 */
RingBufferPtr CreateRingBuffer(size_t sz, size_t elem_sz, int limit_writes);

#endif /* RINGBUFFER_H */