problem using ReadFile/WriteFile in overlapped I/O   

I am sorry if this is in the wrong group. I am making a C program that 
accesses the COM port for reading & writing AT commands to my mobile phone. 
my problem is that I want the reading & writing to take place independently 
and I want it to be completely event driven. I am currently using ReadFile 
with an infinite timeout so that I don't do anything until I receive 
something in the buffer. But I am unable to understand how to issue a 
WriteFile command while I am still waiting for the read to take place. I am 
using the following code:

                DCB dcb;
	HANDLE hCom;
	BOOL fSuccess;
	OVERLAPPED o;
	COMMTIMEOUTS timeouts;
	DWORD dwEvtMask;
	char *pcCommPort = "COM4";  //specify the port to be opened

	hCom = CreateFile( pcCommPort,
                     GENERIC_READ | GENERIC_WRITE, //read & write
                     0,    // comm devices must be opened w/exclusive-access
                     NULL, // no security attributes
                     OPEN_EXISTING, // comm devices must use OPEN_EXISTING
					 FILE_FLAG_OVERLAPPED, //Overlapped I/O enabled
                     NULL  // hTemplate must be NULL for comm devices
                     );

	if (hCom == INVALID_HANDLE_VALUE)
	{
      // Handle the error.
      printf ("CreateFile failed with error %d.\n", GetLastError());
      return (1);
	}

    fSuccess = GetCommState(hCom, &dcb);

 	if (!fSuccess)
 	{
      // Handle the error.
       printf ("GetCommState failed with error %d.\n", GetLastError());
       return (2);
     }

 	// Fill in the DCB: baud=9600 bps, 8 data bits, no parity, and 1 stop bit.

 	dcb.BaudRate = CBR_9600;     // set the baud rate
 	dcb.ByteSize = 8;             // data size, xmit, and rcv
 	dcb.Parity = NOPARITY;        // no parity bit
 	dcb.StopBits = ONESTOPBIT;    // one stop bit

 	fSuccess = SetCommState(hCom, &dcb);

 	if (!fSuccess)
 	{
 		// Handle the error.
 		printf ("SetCommState failed with error %d.\n", GetLastError());
 		return (3);
     }

 	printf ("Serial port %s is successfully reconfigured.\n", pcCommPort);

    //Set port timeout values
    timeouts.ReadIntervalTimeout         = MAXDWORD; //These values ensure 
that the read operation
    timeouts.ReadTotalTimeoutMultiplier  = 0;        //returns immediately 
with the characters that have
    timeouts.ReadTotalTimeoutConstant    = 0;        //already been 
received, even if none are received
    timeouts.WriteTotalTimeoutMultiplier = 0;        //Time-outs not used
    timeouts.WriteTotalTimeoutConstant   = 0;        //for write operation


    if (!SetCommTimeouts(hCom, &timeouts))
    {
        //assert(0);
        printf("Error setting time-outs. %d\n",GetLastError());
        return (1);
    }

    // Set the event mask.

    fSuccess = SetCommMask(hCom, EV_RXCHAR | EV_TXEMPTY);

    if (!fSuccess)
    {
        // Handle the error.
        printf("SetCommMask failed with error %d.\n", GetLastError());
        return(5);
    }

BOOL WriteBuffer(HANDLE hComm,char * lpBuf)
{
   OVERLAPPED osWrite = {0};
   DWORD dwWritten;
   DWORD dwToWrite=strlen(lpBuf);
   BOOL fRes;

   // Create OVERLAPPED structure hEvent.
   osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
   if (osWrite.hEvent == NULL)
      // Error creating overlapped event handle.
      return FALSE;

   // Issue write.
   if (!WriteFile(hComm, lpBuf, dwToWrite, &dwWritten, &osWrite))
   {
      if (GetLastError() != ERROR_IO_PENDING)
      {
         // WriteFile failed, but it isn't delayed. Report error and abort.
         printf("\nWriteFile failed with error %d.\n",GetLastError());
         fRes = FALSE;
      }
      else
      {
         // Write is pending.
         if (!GetOverlappedResult(hComm, &osWrite, &dwWritten, TRUE))
            fRes = FALSE;
         else
         {   // Write operation completed successfully.
            printf("\nWrite operation completed successfully.\n");
            //printf("Bytes written=%d\n",dwWritten);
            fRes = TRUE;
         }
      }
   }
   else
   {
      // WriteFile completed immediately.
      printf("\nWriteFile completed immediately.\n");
      fRes = TRUE;
   }

   CloseHandle(osWrite.hEvent);
   return fRes;
}

int ReadBuffer(HANDLE HCom)
{
    OVERLAPPED osRead = {0};
    DWORD dwRead;
    BOOL fRead;

    // Create OVERLAPPED structure hEvent.
    osRead.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
    if (osRead.hEvent == NULL)
      // Error creating overlapped event handle.
      return (1);

    DWORD dwCommEvent;

    for ( ; ; )
    {
        WaitCommEvent(HCom, &dwCommEvent, &osRead);
        if ( WaitForSingleObject(osRead.hEvent,INFINITE) == WAIT_OBJECT_0)
        {
            char szBuf[100];
            do
            {
                memset(szBuf,0,sizeof(szBuf));
                ReadFile( HCom,szBuf,sizeof(szBuf),&dwRead,&osRead);    
                if(dwRead!=0)
                {
                    printf("%s\n",szBuf);
                }
            }while (dwRead > 0 );
        }
        else
        {
            printf("Waiting for single object failed with error no 
%d\n",GetLastError());
            CloseHandle(osRead.hEvent);
            return (2);
        }
    }
    CloseHandle(osRead.hEvent);
}

date: Mon, 16 Jun 2008 22:12:00 -0700   author:   nk28

Re: problem using ReadFile/WriteFile in overlapped I/O   

"nk28"  schrieb
>I am sorry if this is in the wrong group.

Yep, it is. :) It's about 
http://msdn.microsoft.com/en-us/library/bb318658%28VS.85%29.aspx


Armin

date: Tue, 17 Jun 2008 14:13:56 +0200   author:   Armin Zingler