al_SingleRWRingBuffer.hpp

#ifndef INCLUDE_AL_SINGLE_READER_WRITER_RING_BUFFER_HPP
#define INCLUDE_AL_SINGLE_READER_WRITER_RING_BUFFER_HPP
 
/*  Allocore --
        Multimedia / virtual environment application class library
 
        Copyright (C) 2009. AlloSphere Research Group, Media Arts & Technology,
   UCSB. Copyright (C) 2012. The Regents of the University of California. All
   rights reserved.
 
        Redistribution and use in source and binary forms, with or without
        modification, are permitted provided that the following conditions are
   met:
 
                Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
 
                Redistributions in binary form must reproduce the above
   copyright notice, this list of conditions and the following disclaimer in the
                documentation and/or other materials provided with the
   distribution.
 
                Neither the name of the University of California nor the names
   of its contributors may be used to endorse or promote products derived from
                this software without specific prior written permission.
 
        THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
   OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
   OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
        File description:
        Passing data between a pair of threads without locking
 
        File author(s):
        Graham Wakefield, 2010, grrrwaaa@gmail.com
*/
 
#include <inttypes.h>
#include <cstring>
 
//#include "allocore/system/pstdint.h"
 
namespace al {
 
class SingleRWRingBuffer {
 public:
  SingleRWRingBuffer(size_t sz = 256);
 
  ~SingleRWRingBuffer();
 
  size_t writeSpace() const;
 
  size_t readSpace() const;
 
  size_t write(const char* src, size_t sz);
 
  size_t read(char* dst, size_t sz);
 
  size_t peek(char* dst, size_t sz);
 
  void clear() { mRead = mWrite; }
 
 protected:
  size_t mSize, mWrap;
  size_t mRead, mWrite;
  char* mData;
};
 
inline uint32_t next_power_of_two(uint32_t v) {
  --v;
  v |= v >> 1;
  v |= v >> 2;
  v |= v >> 4;
  v |= v >> 8;
  v |= v >> 16;
  return v + 1;
}
 
inline SingleRWRingBuffer ::SingleRWRingBuffer(size_t sz)
    : mSize(size_t(next_power_of_two(uint32_t(sz)))),
      mWrap(mSize - 1),
      mRead(0),
      mWrite(0) {
  mData = new char[mSize];
}
 
inline SingleRWRingBuffer ::~SingleRWRingBuffer() { delete[] mData; }
 
inline size_t SingleRWRingBuffer ::writeSpace() const {
  const size_t r = mRead;
  const size_t w = mWrite;
  if (r == w) return mWrap;
  return ((mSize + (r - w)) & mWrap) - 1;
}
 
inline size_t SingleRWRingBuffer ::readSpace() const {
  const size_t r = mRead;
  const size_t w = mWrite;
  return (mSize + (w - r)) & mWrap;
}
 
inline size_t SingleRWRingBuffer ::write(const char* src, size_t sz) {
  size_t space = writeSpace();
  sz = sz > space ? space : sz;
  if (sz == 0) return 0;
 
  size_t w = mWrite;
  size_t end = w + sz;
 
  if (end < mSize) {
    memcpy(mData + w, src, sz);
  } else {
    size_t split = mSize - w;
    end &= mWrap;
    memcpy(mData + w, src, split);
    memcpy(mData, src + split, end);
  }
 
  mWrite = end;
  return sz;
}
 
inline size_t SingleRWRingBuffer ::read(char* dst, size_t sz) {
  size_t space = readSpace();
  sz = sz > space ? space : sz;
  if (sz == 0) return 0;
 
  size_t r = mRead;
  size_t end = r + sz;
 
  if (end < mSize) {
    memcpy(dst, mData + r, sz);
  } else {
    size_t split = mSize - r;
    end &= mWrap;
    memcpy(dst, mData + r, split);
    memcpy(dst + split, mData, end);
  }
 
  mRead = end;
  return sz;
}
 
inline size_t SingleRWRingBuffer ::peek(char* dst, size_t sz) {
  size_t space = readSpace();
  sz = sz > space ? space : sz;
  if (sz == 0) return 0;
 
  size_t r = mRead;
  size_t end = r + sz;
 
  if (end < mSize) {
    memcpy(dst, mData + r, sz);
  } else {
    size_t split = mSize - r;
    end &= mWrap;
    memcpy(dst, mData + r, split);
    memcpy(dst + split, mData, end);
  }
  return sz;
}
 
}  // namespace al
 
#endif /* include guard */