1 files changed, 115 insertions, 0 deletions
diff --git a/common/ringbuffer.h b/common/ringbuffer.h
new file mode 100644
index 00000000..2a3797b0
--- /dev/null
+++ b/common/ringbuffer.h
@@ -0,0 +1,115 @@
+#ifndef RINGBUFFER_H
+#define RINGBUFFER_H
+
+#include <atomic>
+#include <memory>
+#include <stddef.h>
+#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 RingBuffer {
+private:
+    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;
+
+public:
+    struct Data {
+        al::byte *buf;
+        size_t len;
+    };
+    using DataPair = std::pair<Data,Data>;
+
+
+    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.
+     */
+    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.
+     */
+    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.
+     */
+    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
+    { 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.
+     */
+    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.
+     */
+    size_t write(const void *src, size_t cnt) noexcept;
+    /** Advance the write pointer `cnt' places. */
+    void writeAdvance(size_t cnt) noexcept
+    { mWritePtr.fetch_add(cnt, std::memory_order_acq_rel); }
+
+    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(size_t sz, size_t elem_sz, int limit_writes);
+
+    DEF_FAM_NEWDEL(RingBuffer, mBuffer)
+};
+using RingBufferPtr = std::unique_ptr<RingBuffer>;
+
+#endif /* RINGBUFFER_H */