Named Pipes and Completion Ports.

Posted on 2003-11-08
Medium Priority
Last Modified: 2013-11-20
Running a simple client that opens a pipe and sends a block of data to the server I have written produces the following output on the server.
Thread: 2308 - Async Read :000007F4
Thread: 3840 - Async Read :000007F4
Thread: 3872 - Async Read :000007F4
connecting pipe
Thread: 2876 - Async Read :000007F4
Thread: 3816 - Async Read :000007F4
Thread: 3440 - Async Read :000007F4
pipe connected
connecting pipe

What I am trying to figure out is why my threads GetQueuedCompletionStatus never ever returns for any of the threads. They do not get woken up. Please don't check the code for memory leaks and other nonsense, I am just trying to get the port to work, so I have tried a few things, and its a little messy, but you should get the idea.

I am doing something in the wrong order or something.

Here is the code.
// Server.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include "winexception.h"

static const PIPE_BUFFER_SIZE      = 0x2000; // 8k
static const PIPE_TIMEOUT            = 0x0400; // 1k milliseconds
static const PIPE_KEY                  = 0x00ff; // recognisable key value.
static const PIPE_THREADS            = 0x0006; // number of wekas.

      char m_achQueueName[512];
       int m_iQueueId;
                       int iQueueId) : m_iQueueId(iQueueId)
            lstrcpyn(m_achQueueName, lpszQueueName, sizeof(m_achQueueName));
      WORKFLOWDATA() : m_iQueueId(0)
            memset(m_achQueueName, 0, sizeof(m_achQueueName));

      HANDLE m_hCp;
      HANDLE m_hPipe;

      ASYNC_CONTEXT(HANDLE hCompletionPort,
                          HANDLE hPipe) : m_hCp(hCompletionPort),
                                                    m_hPipe(hPipe) {};

      HANDLE GetCompletionHandle() { return m_hCp; }
      HANDLE GetPipeHandle() { return m_hPipe; }

DWORD WINAPI AsyncCompletionPortThreadProcessor(LPVOID lpParam)

      DWORD dwTransferred = 0L;
      DWORD dwBytesRead = 0L;
      ULONG ulCompletionKey = 0L;
      OVERLAPPED ovl = {0};
       LPOVERLAPPED lpOverlapped = &ovl;
      ASYNC_CONTEXT* pParameters = (ASYNC_CONTEXT*) lpParam;

      while(1) {
            std::cout << "Thread: " << GetCurrentThreadId() << " - Async Read :" << pParameters->GetCompletionHandle() << std::endl;
            BOOL bStatus = GetQueuedCompletionStatus(pParameters->GetCompletionHandle(),
            if (!bStatus || !lpOverlapped) {
                  // FIXME:Craig some logging before continue.      
                  std::cout << "Error and continue" << std::endl;

            std::cout << "reading..." << std::endl;
            //std::cout << GetCurrentThreadId() << ":" << wfd.m_iQueueId << wfd.m_achQueueName << std::endl;
      return 0;

void StartService()
      HANDLE hPipe = ::CreateNamedPipe("\\\\.\\pipe\\workflow",
                                                    PIPE_ACCESS_DUPLEX | FILE_FLAG_OVERLAPPED,
                                               PIPE_WAIT                         // Wait on messages.
                                                       | PIPE_READMODE_MESSAGE           // Specify byte pipe.
                                                       | PIPE_TYPE_MESSAGE,
      assert(INVALID_HANDLE_VALUE != hPipe);
      HANDLE hCp = ::CreateIoCompletionPort(INVALID_HANDLE_VALUE,
      assert(INVALID_HANDLE_VALUE != hCp);
      HANDLE hEvent = ::CreateEvent(0,
      assert(0 != hEvent);
      std::cout << hCp << std::endl;
      ASYNC_CONTEXT* pParameters = new ASYNC_CONTEXT(hCp, hPipe);
      for (int i = 0; i < PIPE_THREADS; i++) {
            HANDLE hThread = ::CreateThread(
            ::SetThreadPriority(hThread, THREAD_PRIORITY_BELOW_NORMAL);            
            ::CloseHandle(hThread); // We don't need these any more, the threads will run.


      HANDLE hPipeCP = ::CreateIoCompletionPort(hPipe,
      assert(0 != hPipeCP);

      //OVERLAPPED ov = {0};
      DWORD dwBytesRead = 0;
      while(1) {

            OVERLAPPED* ov = new OVERLAPPED;
            std::cout << "connecting pipe" << std::endl;
            memset(ov, 0, sizeof(OVERLAPPED));
            ov->hEvent = ((HANDLE)((DWORD)hEvent|0x1));
            BOOL bConnected = ::ConnectNamedPipe(hPipe, ov);
            WaitForSingleObject(hEvent,      INFINITE);

            BOOL bRead = ReadFile(
                  new char[8196],//&wfd,
            if (bRead == FALSE) {
                  assert(GetLastError() == ERROR_IO_PENDING) ;
                        std::cout << "Pending...." << std::endl;

            std::cout << "pipe connected" << std::endl;
      std::cout << "pipe connected" << std::endl;

int _tmain(int argc, _TCHAR* argv[])
      return 0;
}// Server.cpp : Defines the entry point for the console application.
Question by:cmain
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
LVL 16

Expert Comment

ID: 9707462
I have no experience with completion ports, but I've felt surprised with the lowest-bit setting in the hEvent field in the OVERLAPPED structure, and found this in the MSDN docs :

Even if you have passed the function a file handle associated with a completion port and a valid OVERLAPPED structure, an application can prevent completion port notification. This is done by specifying a valid event handle for the hEvent member of the OVERLAPPED structure, and setting its low-order bit. A valid event handle whose low-order bit is set keeps I/O completion from being queued to the completion port.

If you're preventing it to happen, it's about normal that it doesn't, what do you think ?
LVL 48

Accepted Solution

AlexFM earned 750 total points
ID: 9707773
ConnectNamedPipe should be handled using completion port, exactly as ReadFile. ReadFile should be issued after ConnectNamedPipe is completed (and also after previous ReadFile is completed). To differentiate these two cases (GetQueuedCompletionStatus is waked up by ConnectNamedPipe or ReadFile), you need to pass additional information with lpOverlapped parameter. You can see how this is done in the following sample:


See OVERLAPPEDPLUS structure which is passed to GetQueuedCompletionStatus and contains additional field defining type of I/O operation.

However, before making these changes, try to wake up GetQueuedCompletionStatus with ConnectNamedPipe call. If this succeded, you are in the right way.

Featured Post

On Demand Webinar: Networking for the Cloud Era

Ready to improve network connectivity? Watch this webinar to learn how SD-WANs and a one-click instant connect tool can boost provisions, deployment, and management of your cloud connection.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This is to be the first in a series of articles demonstrating the development of a complete windows based application using the MFC classes.  I’ll try to keep each article focused on one (or a couple) of the tasks that one may meet.   Introductio…
Have you tried to learn about Unicode, UTF-8, and multibyte text encoding and all the articles are just too "academic" or too technical? This article aims to make the whole topic easy for just about anyone to understand.
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
Michael from AdRem Software explains how to view the most utilized and worst performing nodes in your network, by accessing the Top Charts view in NetCrunch network monitor (https://www.adremsoft.com/). Top Charts is a view in which you can set seve…
Suggested Courses

770 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question