alc/ringbuffer.h

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