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non-blocking reads of stdin in native child of cygwin process

I can do a non-blocking read from standard input in a native C program run in a cmd window. It involves WaitForSingleObject on the return value from GetStdHandle(STD_INPUT_HANDLE). I could use some sample code for doing the equivalent thing when run from mintty/bash or cygwin.bat/bash. The story of what I've tried so far follows.

When running a native C program from mintty/bash or cygwin.bat/bash GetStdHandle returns a pipe, not a console handle so WaitForMultipleObjects doesn't work...or at least not the same way. The docs don't say it works on named pipes and for me it returns WAIT_OBJECT_0 whether there's something to read or not.

I've got my hands on the name of the pipe via GetNamedPipeInfo and GetFileInformationByHandleEx -- something like \\pipe\.\cygwin-dcb128a9c32912c6-pty1-from-master. This matches what I see in usr/src/cygwin-1.7.15/winsup/cygwin/ (tty::not_allocated) and (fhandler_pipe::create).

I'm running with an elevated token but I still get access denied trying to use that handle in CreateFileW. I'm not sure this is the right call to make but it works for me in other scenarios for non-blocking IO on named pipes (when followed by ReadFile w/ an OVERLAPPED structure, ERROR_IO_PENDING, WaitForMultipleObjects, GetOverlappedResult, etc.).

In case it's relevant, GetNamedPipe info reports 0x05 (PIPE_SERVER_END | PIPE_TYPE_MESSAGE) for the return value of GetStdHandle(STD_INPUT_HANDLE) whether the CYGWIN environment variable contains pipe_byte or not.

As well, GetNamedPipeHandleState reports a state of 0x00 (also independent of CYGWIN=pipe_byte as far as I can tell) which I interpret as a blocking, byte-mode pipe. This matches my reading of the CreateNamedPipe call in So even if I wasn't getting access denied from CreateFileW I still do think I could use my standard input handle in a call to ReadFile that specifies an OVERLAPPED structure, etc. SetNamedPipeHandleState is tempting, but the docs there ( for PIPE_NOWAIT say:

"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."

I see that fhandler_pty_master::setup in does this so maybe the docs are warning against something that actually works.

Any chance someone out there has come up with a way to do this? I imagine this isn't (very high) on the priority list for cygwin but with any luck I haven't crossed the line by trying to get help here.

Thanks much for your time.


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