satchboost has asked for the wisdom of the Perl Monks concerning the following question:

I've got a PERL app running on Unix and one of the things it does is select() on STDIN. A friend of mine mentioned that this is impossible to do in Windows. Is this true?

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(tye)Re: Selecting on STDIN in Win32
by tye (Sage) on Mar 29, 2001 at 02:21 UTC

    Yes, Win32's select only works on TCP sockets. Worse, I haven't found a reasonable way to poll STDIN under Windows whether STDIN is a "console" or not (that is, no way to see if characters are pending from STDIN, set a timeout on a read from STDIN, or just make STDIN nonblocking). Someone please prove me wrong!

    One alternative is to rework the script to use a TCP socket connected to localhost so you can use select(), though the odds of that working for your problem seem small.

            - tye (but my friends call me "Tye")
      I haven't found a reasonable way to poll STDIN under Windows whether STDIN is a "console" or not (that is, no way to see if characters are pending from STDIN, set a timeout on a read from STDIN, or just make STDIN nonblocking). Someone please prove me wrong!
      If STDIN is indeed the input stream for a console (not redirected), then WaitForSingleObject et.al. with a timeout of zero will do just that—check the state without blocking.

      On the CONIN$ device, a handle is signaled when input is waiting to be read. Other file handles don't do that.

      In a more general case, the way to emulate it is with a helper thread that does a blocking read, buffers what it did read, and signals the main program that it got something. Or, more nativly, issue an asyncronous read and get signaled when that particular request is fulfilled.

      In that last case, in general, instead of using select to watch for input and then read it, you issue async read requests for all the inputs, then wait for (any) to complete.

      —John

Re: Selecting on STDIN in Win32
by satchboost (Scribe) on Mar 29, 2001 at 02:30 UTC
    tye -

    Thanx for the confirmation. So, given that, I created a listening socket for servers. Unfortunately, my select() call keeps returning -1, even though I've got a timeout of 30sec on it. I even check the timeleft and it is still 30sec. This stupid Win32 port is getting more annoying every day. :(

      As always, post a minimal example (using cut'n'paste, not retyping) along with exactly how it fails. (:

              - tye (but my friends call me "Tye")