Question

I have a thread that constantly looks for new data and if the data is not already in the serial buffer, ReadFile and GetOverlappedResult seem to tell me there’s data, and that it read it, but not transfer it into my buffer…

func read()
{
    if(state == 0)
    {
        memset(bytes, '\0', sizeof(amount_to_read));

        readreturn = ReadFile(h, bytes, amount_to_read,NULL, osReader);
        if(readreturn <= 0)
        {
            errorcode = GetLastError();
            if(errorcode != ERROR_IO_PENDING)
            {
                SetEAIError(ERROR_INTERNALERROR);
                return -1;
            }
        }
    }

    if (GetOverlappedResult(h, osReader, &dwRead, FALSE) == false)
    {
        errorcode = GetLastError();

        if (errorcode == ERROR_IO_INCOMPLETE || errorcode == 0)
        {
            if(dwRead > 0)
            {
                return 1;
            }
            //timeout
            SetEAIError(ERROR_EAITIMEOUT);
            return -1;
        }
        else
        {
            //other error 
            SetEAIError(ERROR_WIN_ERROR);
            return -1;
        }
    }
    else
    {
        //read succeded, check if we read the amount required
        if(dwRead != amount_to_read)
        {
            if(dwRead == 0)
            {
                //nothing read, treat as timeout
                SetEAIError(ERROR_EAINOREAD);
                return -1;
            }
            else
            {
                //memcpy_s(bytes, sizeof(bytes), readbuf, dwRead);
                SetEAIError(ERROR_PARTIALREAD);
                *_bytesRead = dwRead;
                return -1;
            }
        }
        else
        {
            if(strlen((char*)bytes) == 0)
            {
                //nothing read, treat as timeout
                SetEAIError(ERROR_EAINOREAD);
                return -1;
            }
            //memcpy_s(bytes, sizeof(bytes), readbuf, dwRead);
            *_bytesRead = dwRead;
            return 0;
        }
    }
}

This is what the error codes mean:

• ERROR_TIMEOUT – switches the state to 1 so that it does not read again, which calls GetOverlappedResult again

• INTERNALERROR,ERROR_EAINOREAD – it resets state to 0

• ERROR_PARTIALREAD – starts a new read with new amount of bytes to read

If I swtich GetOverlappedResult to blocking (pass TRUE) it works every time.
If I switch my thread to only read when I know there is data there it works every time.

But if there is not data there, when there is data there it seems to “lose” the data, it my read amount parameter dwRead shows the correct number of bytes read (can see it read with a port monitor) but the bytes are not stored in my char*.

I constantly get ERROR_EAINOREAD

What am I doing wrong?

I do not want to use flags, I want to just use ReadFile and GetOverlappedResult, I should be able to accomplish this with the code I have……. I assume

Answer 1

The problem was exactly what was stated the data was getting lost… the REASON it was getting lost is because the bytes parameter passed into the readfile is a local variable in the parents thread. being local it gets re initialized each cycle so after I come into the read again, skip the readfile and go to the overlappedresults, I am now potentially working with a different area of memory