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     std::atomic<size_t> mWritePtr{0u};
  29     std::atomic<size_t> mReadPtr{0u};
  30     size_t mWriteSize{0u};
  31     size_t mSizeMask{0u};
  32     size_t mElemSize{0u};
  33
  34     al::FlexArray<al::byte, 16> mBuffer;
  35
  36     RingBuffer(const size_t count) : mBuffer{count} { }
  37
  38     /** Reset the read and write pointers to zero. This is not thread safe. */
  39     void reset() noexcept;
  40
  41     /**
  42      * The non-copying data reader. Returns two ringbuffer data pointers that
  43      * hold the current readable data. If the readable data is in one segment
  44      * the second segment has zero length.
  45      */
  46     ll_ringbuffer_data_pair getReadVector() const noexcept;
  47     /**
  48      * The non-copying data writer. Returns two ringbuffer data pointers that
  49      * hold the current writeable data. If the writeable data is in one segment
  50      * the second segment has zero length.
  51      */
  52     ll_ringbuffer_data_pair getWriteVector() const noexcept;
  53
  54     /**
  55      * Return the number of elements available for reading. This is the number
  56      * of elements in front of the read pointer and behind the write pointer.
  57      */
  58     size_t readSpace() const noexcept;
  59     /**
  60      * The copying data reader. Copy at most `cnt' elements into `dest'.
  61      * Returns the actual number of elements copied.
  62      */
  63     size_t read(void *dest, size_t cnt) noexcept;
  64     /**
  65      * The copying data reader w/o read pointer advance. Copy at most `cnt'
  66      * elements into `dest'. Returns the actual number of elements copied.
  67      */
  68     size_t peek(void *dest, size_t cnt) const noexcept;
  69     /** Advance the read pointer `cnt' places. */
  70     void readAdvance(size_t cnt) noexcept;
  71
  72     /**
  73      * Return the number of elements available for writing. This is the number
  74      * of elements in front of the write pointer and behind the read pointer.
  75      */
  76     size_t writeSpace() const noexcept;
  77     /**
  78      * The copying data writer. Copy at most `cnt' elements from `src'. Returns
  79      * the actual number of elements copied.
  80      */
  81     size_t write(const void *src, size_t cnt) noexcept;
  82     /** Advance the write pointer `cnt' places. */
  83     void writeAdvance(size_t cnt) noexcept;
  84
  85     DEF_FAM_NEWDEL(RingBuffer, mBuffer)
  86 };
  87 using RingBufferPtr = std::unique_ptr<RingBuffer>;
  88
  89
  90 /**
  91  * Create a new ringbuffer to hold at least `sz' elements of `elem_sz' bytes.
  92  * The number of elements is rounded up to the next power of two (even if it is
  93  * already a power of two, to ensure the requested amount can be written).
  94  */
  95 RingBufferPtr CreateRingBuffer(size_t sz, size_t elem_sz, int limit_writes);
  96
  97 #endif /* RINGBUFFER_H */