From the msdn: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipc/base/se... """PIPE_NOWAIT 0x00000001 Nonblocking mode is enabled. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always return immediately. Note that nonblocking mode is supported for compatibility with Microsoft® LAN Manager version 2.0 and should not be used to achieve asynchronous input and output (I/O) with named pipes. """ P.S. I really can't believe that win32 support for asynchronous I/O works with named pipes but not with anonymous pipes... By the way, instead of using a polling, why not to use a separate thread that puts data into a DeferredQueue? P.S.2: From: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipc/base/an... """Anonymous pipes are implemented using a named pipe with a unique name. Therefore, you can often pass a handle to an anonymous pipe to a function that requires a handle to a named pipe. """ And from: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/bas... """A child process can inherit [...] * Open handles returned by the CreateFile function. This includes handles to files, console input buffers, console screen buffers, named pipes, serial communication devices, and mailslots. * Open handles to process, thread, mutex, event, semaphore, named-pipe, anonymous-pipe, and file-mapping objects. These are returned by the CreateProcess, CreateThread, CreateMutex, CreateEvent, CreateSemaphore, CreateNamedPipe, CreatePipe, and CreateFileMapping functions, respectively. """ So, why not to create a named pipe with an unique name, know to both the parent and the child process, as an example using an enviroment variable? I think that using named pipes can simplify the _dumbwin32proc. Moreover polling a named pipe is not an efficient operation (reading the author of "Windows System Programming"). Lastly, the parent process, after creating a named pipe instance, can wait for a client connection using ConnectNamedPipe. Regards Manlio Perillo