C++ Atomic Compare Exchange

gistfile1.txt

struct BufferPos{
    uint8_t write;
    uint8_t read;
};

std::atomic<BufferPos> bufferPos;

--

Thread 1
BufferPos currPos = bufferPos.load(std::memory_order_relaxed);

BufferPos oldBufferPos = bufferPos.load(std::memory_order_relaxed);
BufferPos newBufferPos;
do{
    newBufferPos.write = (oldBufferPos.write + 1) % ARRAYSIZE;
    if(newBufferPos.write == oldBufferPos.read){
        newBufferPos.write = (oldBufferPos.read + 1) % ARRAYSIZE;
    }
    newBufferPos.read = oldBufferPos.read;
}
while(!bufferPos.compare_exchange_weak(oldBufferPos, newBufferPos));
--
Thread 2
uint8_t counter = 0;
while(counter != 128){
    BufferPos oldBufferPos = bufferPos.load(std::memory_order_relaxed);
    BufferPos newBufferPos;
    do{
        newBufferPos.read = (oldBufferPos.read - 1) % ARRAYSIZE;
        if(newBufferPos.read == oldBufferPos.write){
            newBufferPos.read = (oldBufferPos.write - 1) % ARRAYSIZE;
        }
        newBufferPos.write = oldBufferPos.write;
    }
    while(!bufferPos.compare_exchange_weak(oldBufferPos, newBufferPos));

    BufferPos currPos = bufferPos.load(std::memory_order_relaxed);
    if(bufferPosToSeqNum[currPos.read] == seqNum){
        std::memcpy(&destBuffer, &bufferArray[currPos.read*BUFFERSIZE], messageSize[currPos.read]);
        return messageSize[currPos.read];
    }
    counter++;
}