common/ringbuffer.h

   1 #ifndef RINGBUFFER_H
   2 #define RINGBUFFER_H
   3
   4 #include <atomic>
   5 #include <memory>
   6 #include <stddef.h>
   7 #include <utility>
   8
   9 #include "albyte.h"
  10 #include "almalloc.h"
  11
  12
  13 /* NOTE: This lockless ringbuffer implementation is copied from JACK, extended
  14  * to include an element size. Consequently, parameters and return values for a
  15  * size or count is in 'elements', not bytes. Additionally, it only supports
  16  * single-consumer/single-provider operation.
  17  */
  18
  19 struct RingBuffer {
  20 private:
  21     std::atomic<size_t> mWritePtr{0u};
  22     std::atomic<size_t> mReadPtr{0u};
  23     size_t mWriteSize{0u};
  24     size_t mSizeMask{0u};
  25     size_t mElemSize{0u};
  26
  27     al::FlexArray<al::byte, 16> mBuffer;
  28
  29 public:
  30     struct Data {
  31         al::byte *buf;
  32         size_t len;
  33     };
  34     using DataPair = std::pair<Data,Data>;
  35
  36
  37     RingBuffer(const size_t count) : mBuffer{count} { }
  38
  39     /** Reset the read and write pointers to zero. This is not thread safe. */
  40     void reset() noexcept;
  41
  42     /**
  43      * The non-copying data reader. Returns two ringbuffer data pointers that
  44      * hold the current readable data. If the readable data is in one segment
  45      * the second segment has zero length.
  46      */
  47     DataPair getReadVector() const noexcept;
  48     /**
  49      * The non-copying data writer. Returns two ringbuffer data pointers that
  50      * hold the current writeable data. If the writeable data is in one segment
  51      * the second segment has zero length.
  52      */
  53     DataPair getWriteVector() const noexcept;
  54
  55     /**
  56      * Return the number of elements available for reading. This is the number
  57      * of elements in front of the read pointer and behind the write pointer.
  58      */
  59     size_t readSpace() const noexcept
  60     {
  61         const size_t w{mWritePtr.load(std::memory_order_acquire)};
  62         const size_t r{mReadPtr.load(std::memory_order_acquire)};
  63         return (w-r) & mSizeMask;
  64     }
  65
  66     /**
  67      * The copying data reader. Copy at most `cnt' elements into `dest'.
  68      * Returns the actual number of elements copied.
  69      */
  70     size_t read(void *dest, size_t cnt) noexcept;
  71     /**
  72      * The copying data reader w/o read pointer advance. Copy at most `cnt'
  73      * elements into `dest'. Returns the actual number of elements copied.
  74      */
  75     size_t peek(void *dest, size_t cnt) const noexcept;
  76     /** Advance the read pointer `cnt' places. */
  77     void readAdvance(size_t cnt) noexcept
  78     { mReadPtr.fetch_add(cnt, std::memory_order_acq_rel); }
  79
  80
  81     /**
  82      * Return the number of elements available for writing. This is the number
  83      * of elements in front of the write pointer and behind the read pointer.
  84      */
  85     size_t writeSpace() const noexcept
  86     {
  87         const size_t w{mWritePtr.load(std::memory_order_acquire)};
  88         const size_t r{mReadPtr.load(std::memory_order_acquire) + mWriteSize - mSizeMask};
  89         return (r-w-1) & mSizeMask;
  90     }
  91
  92     /**
  93      * The copying data writer. Copy at most `cnt' elements from `src'. Returns
  94      * the actual number of elements copied.
  95      */
  96     size_t write(const void *src, size_t cnt) noexcept;
  97     /** Advance the write pointer `cnt' places. */
  98     void writeAdvance(size_t cnt) noexcept
  99     { mWritePtr.fetch_add(cnt, std::memory_order_acq_rel); }
 100
 101     size_t getElemSize() const noexcept { return mElemSize; }
 102
 103     /**
 104      * Create a new ringbuffer to hold at least `sz' elements of `elem_sz'
 105      * bytes. The number of elements is rounded up to the next power of two
 106      * (even if it is already a power of two, to ensure the requested amount
 107      * can be written).
 108      */
 109     static std::unique_ptr<RingBuffer> Create(size_t sz, size_t elem_sz, int limit_writes);
 110
 111     DEF_FAM_NEWDEL(RingBuffer, mBuffer)
 112 };
 113 using RingBufferPtr = std::unique_ptr<RingBuffer>;
 114
 115 #endif /* RINGBUFFER_H */