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Named Pipes and Completion Ports.

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.
1 Solution
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 ?
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.

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