Lock Free Single Producer Single Consumer Ring Buffer

ringbuffer.c

// Copyright (C) 2015 by Benjamin 'BeRo' Rosseaux
// licensed under CC0 1.0 Universal (CC0 1.0) Public Domain Dedication ( http://creativecommons.org/publicdomain/zero/1.0/ )

// Warning: Untested, written from scratch directly as a GitHubGist. It should only show the base idea behind it.

#define RingBufferInt int
#define RingBufferAtomicInt int

typedef int TRingBufferItem;

typedef TRingBufferItem *PRingBufferItem;

typedef struct {
  RingBufferInt Size;
#ifndef WithOutFilled
  RingBufferAtomicInt Filled;
#endif
  RingBufferAtomicInt ReadPos;
  RingBufferAtomicInt WritePos;
  PRingBufferItem Data;  
} TRingBuffer;

typedef TRingBuffer *PRingBuffer;

void RingBufferCreate(PRingBuffer RingBuffer, RingBufferInt Size){
  memset(RingBuffer, 0, sizeof(TRingBuffer));
  RingBuffer->Size = Size;
  RingBuffer->Data = malloc(Size * sizeof(TRingBufferItem));
  memset(RingBuffer->Data, 0, Size * sizeof(TRingBufferItem));
}

void RingBufferDestroy(PRingBuffer RingBuffer){
  free(RingBuffer->Data);
  memset(RingBuffer, 0, sizeof(TRingBuffer));
}

inline RingBufferInt RingBufferUsed(PRingBuffer RingBuffer){
#ifdef WithOutFilled
  RingBufferInt LocalReadPos = atomic_load(&RingBuffer->ReadPos);
  RingBufferInt LocalWritePos = atomic_load(&RingBuffer->WritePos);
  return (LocalWritePos >= LocalReadPos) ? (LocalWritePos - LocalReadPos) : ((RingBuffer->Size - LocalReadPos) + LocalWritePos);
#else
  return atomic_load(&RingBuffer->Filled);
#endif
}

inline RingBufferInt RingBufferFree(PRingBuffer RingBuffer){
#ifdef WithOutFilled
  RingBufferAtomicInt LocalReadPos = atomic_load(&RingBuffer->ReadPos);
  RingBufferAtomicInt LocalWritePos = atomic_load(&RingBuffer->WritePos);
  return RingBuffer->Size - ((LocalWritePos >= LocalReadPos) ? (LocalWritePos - LocalReadPos) : ((RingBuffer->Size - LocalReadPos) + LocalWritePos));
#else
  return RingBuffer->Size - atomic_load(&RingBuffer->Filled);
#endif
}

RingBufferInt RingBufferRead(PRingBuffer RingBuffer, PRingBufferItem Buffer, RingBufferInt Count){
  RingBufferInt Size = RingBuffer->Size, Total, LocalReadPos = atomic_load(&RingBuffer->ReadPos), ToRead, Len;
#ifdef WithOutFilled
  RingBufferInt LocalWritePos = atomic_load(&RingBuffer->WritePos);
  Total = Size - ((LocalWritePos >= LocalReadPos) ? (LocalWritePos - LocalReadPos) : ((RingBuffer->Size - LocalReadPos) + LocalWritePos));
#else
  Total = RingBuffer->Filled;
#endif
  Len = Count;
  if(Len > Total){
    Len = Total
  }else{
    Total = Len;
  }
  while(Len > 0){
    if((LocalReadPos + Len) > Size){
      ToRead = Size - LocalReadPos;
      memcpy(Buffer, &RingBuffer->Data[LocalReadPos], ToRead * sizeof(TRingBufferItem));
      Buffer += ToRead;
      Len -= ToRead;
      LocalReadPos = 0;
    }else{
      memcpy(Buffer, &RingBuffer->Data[LocalReadPos], Len * sizeof(TRingBufferItem));
      LocalReadPos += Len;
      break;
    }
  }
  while(LocalReadPos >= Size){
    LocalReadPos -= Size;
  } 
  atomic_store(&RingBuffer->ReadPos, LocalReadPos);
#ifndef WithOutFilled
  atomic_fetch_sub(&RingBuffer->Filled, Bytes);        
#endif
  return Total;
}

RingBufferInt RingBufferWrite(PRingBuffer RingBuffer, PRingBufferItem Buffer, RingBufferInt Count){
  RingBufferInt Size = RingBuffer->Size, Total, LocalWritePos, ToWrite, Len;
#ifdef WithOutFilled
  RingBufferInt LocalReadPos = atomic_load(&RingBuffer->ReadPos);
  LocalWritePos = atomic_load(&RingBuffer->WritePos);
  Total = Size - ((LocalWritePos >= LocalReadPos) ? (LocalWritePos - LocalReadPos) : ((RingBuffer->Size - LocalReadPos) + LocalWritePos));
#else
  Total = Size - RingBuffer->Filled;
#endif
  Len = Count;
  if(Total >= Len){
    if(Len > Total){
      Len = Total;
    }
#ifndef WithOutFilled
    LocalWritePos = atomic_load(&RingBuffer->WritePos);
#endif
    while(Len > 0){
      if((LocalWritePos + Len) > Size){
        ToWrite = Size - LocalWritePos;
        memcpy(&RingBuffer->Data[LocalWritePos], Buffer, ToWrite * sizeof(TRingBufferItem));
        Buffer += ToWrite;
        Len -= ToWrite;
        LocalWritePos = 0;
      }else{
        memcpy(&RingBuffer->Data[LocalWritePos], Buffer, Len * sizeof(TRingBufferItem));
        LocalWritePos += Len;
        break;
      } 
    }
    while(LocalWritePos >= Size){
      LocalWritePos -= Size;
    }
    atomic_store(&RingBuffer->WritePos, LocalWritePos);
#ifndef WithOutFilled
    atomic_fetch_add(&RingBuffer->Filled, Bytes);        
#endif
    return Total;
  }else{
    return 0;
  }
}