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#ifndef RINGBUFFER_H
#define RINGBUFFER_H
#include <atomic>
#include <cstddef>
#include <memory>
#include <utility>
#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 RingBuffer {
private:
std::atomic<std::size_t> mWritePtr{0u};
std::atomic<std::size_t> mReadPtr{0u};
std::size_t mWriteSize{0u};
std::size_t mSizeMask{0u};
std::size_t mElemSize{0u};
al::FlexArray<std::byte, 16> mBuffer;
public:
struct Data {
std::byte *buf;
std::size_t len;
};
using DataPair = std::pair<Data,Data>;
RingBuffer(const std::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.
*/
DataPair 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.
*/
DataPair 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.
*/
std::size_t readSpace() const noexcept
{
const size_t w{mWritePtr.load(std::memory_order_acquire)};
const size_t r{mReadPtr.load(std::memory_order_acquire)};
return (w-r) & mSizeMask;
}
/**
* The copying data reader. Copy at most `cnt' elements into `dest'.
* Returns the actual number of elements copied.
*/
std::size_t read(void *dest, std::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.
*/
std::size_t peek(void *dest, std::size_t cnt) const noexcept;
/** Advance the read pointer `cnt' places. */
void readAdvance(std::size_t cnt) noexcept
{ mReadPtr.fetch_add(cnt, std::memory_order_acq_rel); }
/**
* 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.
*/
std::size_t writeSpace() const noexcept
{
const size_t w{mWritePtr.load(std::memory_order_acquire)};
const size_t r{mReadPtr.load(std::memory_order_acquire) + mWriteSize - mSizeMask};
return (r-w-1) & mSizeMask;
}
/**
* The copying data writer. Copy at most `cnt' elements from `src'. Returns
* the actual number of elements copied.
*/
std::size_t write(const void *src, std::size_t cnt) noexcept;
/** Advance the write pointer `cnt' places. */
void writeAdvance(std::size_t cnt) noexcept
{ mWritePtr.fetch_add(cnt, std::memory_order_acq_rel); }
std::size_t getElemSize() const noexcept { return mElemSize; }
/**
* 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).
*/
static std::unique_ptr<RingBuffer> Create(std::size_t sz, std::size_t elem_sz, int limit_writes);
DEF_FAM_NEWDEL(RingBuffer, mBuffer)
};
using RingBufferPtr = std::unique_ptr<RingBuffer>;
#endif /* RINGBUFFER_H */
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