Question

Is it possible to use overlapped I/O with an anonymous pipe? CreatePipe() does not have any way of specifying FILE_FLAG_OVERLAPPED, so I assume ReadFile() will block, even if I supply an OVERLAPPED-structure.

Answer 1

Here is an implementation for an anonymous pipe function with the possibility to specify FILE_FLAG_OVERLAPPED:

/******************************************************************************\ *       This is a part of the Microsoft Source Code Samples.  *       Copyright 1995 - 1997 Microsoft Corporation. *       All rights reserved.  *       This source code is only intended as a supplement to  *       Microsoft Development Tools and/or WinHelp documentation. *       See these sources for detailed information regarding the  *       Microsoft samples programs. \******************************************************************************/  /*++ Copyright (c) 1997  Microsoft Corporation Module Name:     pipeex.c Abstract:     CreatePipe-like function that lets one or both handles be overlapped Author:     Dave Hart  Summer 1997 Revision History: --*/  #include <windows.h> #include <stdio.h>  static volatile long PipeSerialNumber;  BOOL APIENTRY MyCreatePipeEx(     OUT LPHANDLE lpReadPipe,     OUT LPHANDLE lpWritePipe,     IN LPSECURITY_ATTRIBUTES lpPipeAttributes,     IN DWORD nSize,     DWORD dwReadMode,     DWORD dwWriteMode     )  /*++ Routine Description:     The CreatePipeEx API is used to create an anonymous pipe I/O device.     Unlike CreatePipe FILE_FLAG_OVERLAPPED may be specified for one or     both handles.     Two handles to the device are created.  One handle is opened for     reading and the other is opened for writing.  These handles may be     used in subsequent calls to ReadFile and WriteFile to transmit data     through the pipe. Arguments:     lpReadPipe - Returns a handle to the read side of the pipe.  Data         may be read from the pipe by specifying this handle value in a         subsequent call to ReadFile.     lpWritePipe - Returns a handle to the write side of the pipe.  Data         may be written to the pipe by specifying this handle value in a         subsequent call to WriteFile.     lpPipeAttributes - An optional parameter that may be used to specify         the attributes of the new pipe.  If the parameter is not         specified, then the pipe is created without a security         descriptor, and the resulting handles are not inherited on         process creation.  Otherwise, the optional security attributes         are used on the pipe, and the inherit handles flag effects both         pipe handles.     nSize - Supplies the requested buffer size for the pipe.  This is         only a suggestion and is used by the operating system to         calculate an appropriate buffering mechanism.  A value of zero         indicates that the system is to choose the default buffering         scheme. Return Value:     TRUE - The operation was successful.     FALSE/NULL - The operation failed. Extended error status is available         using GetLastError. --*/  {   HANDLE ReadPipeHandle, WritePipeHandle;   DWORD dwError;   UCHAR PipeNameBuffer[ MAX_PATH ];    //   // Only one valid OpenMode flag - FILE_FLAG_OVERLAPPED   //    if ((dwReadMode | dwWriteMode) & (~FILE_FLAG_OVERLAPPED)) {     SetLastError(ERROR_INVALID_PARAMETER);     return FALSE;   }    //   //  Set the default timeout to 120 seconds   //    if (nSize == 0) {     nSize = 4096;   }    sprintf( PipeNameBuffer,            '\\\\.\\Pipe\\RemoteExeAnon.%08x.%08x',            GetCurrentProcessId(),            InterlockedIncrement(&PipeSerialNumber)          );    ReadPipeHandle = CreateNamedPipeA(                        PipeNameBuffer,                        PIPE_ACCESS_INBOUND | dwReadMode,                        PIPE_TYPE_BYTE | PIPE_WAIT,                        1,             // Number of pipes                        nSize,         // Out buffer size                        nSize,         // In buffer size                        120 * 1000,    // Timeout in ms                        lpPipeAttributes                        );    if (! ReadPipeHandle) {     return FALSE;   }    WritePipeHandle = CreateFileA(                       PipeNameBuffer,                       GENERIC_WRITE,                       0,                         // No sharing                       lpPipeAttributes,                       OPEN_EXISTING,                       FILE_ATTRIBUTE_NORMAL | dwWriteMode,                       NULL                       // Template file                     );    if (INVALID_HANDLE_VALUE == WritePipeHandle) {     dwError = GetLastError();     CloseHandle( ReadPipeHandle );     SetLastError(dwError);     return FALSE;   }    *lpReadPipe = ReadPipeHandle;   *lpWritePipe = WritePipeHandle;   return( TRUE ); }