New subject: [polyml] playing with Posix fork/exec/dup2 etc

18 Mar 2016


      Under 5.5.1, and after compiling with polyc, the code below gives an assertion violation and core dump:
...
$ ./a.out
In parent - reading
Assertion failed: (save_vec_addr < save_vec+1000), function push, file save_vec.cpp, line 70.
Abort trap: 6
(That's the OSX wording.  I get something very similar under Linux.)
I may well be making a hash of my POSIX programming, but I'd still hope for an exception rather than a core dump.
Michael
- - - -
fun mkTIO_instream fd =
  let
    open Posix.IO
    val (flags,_) = getfl fd
    val rdr = mkTextReader { fd = fd, name = "",
                             initBlkMode = O.anySet (flags, O.nonblock) }
  in
    TextIO.mkInstream (TextIO.StreamIO.mkInstream (rdr, ""))
  end
fun main() =
  let
    open Posix.Process Posix.IO
    val {infd,outfd} = pipe()
  in
    case fork () of
        NONE =>
        let
          val () = dup2{old = outfd, new = Posix.FileSys.stdout}
          val () = List.app close [infd, outfd]
        in
          exec("/bin/ls", ["ls", "."])
        end
      | SOME pid =>
        let
          val _ = print "In parent - reading\n"
          val strm = mkTIO_instream infd
          fun recurse () =
            case TextIO.inputLine strm of
                NONE => ()
              | SOME s => (print ("Child: " ^ s); recurse())
        in
          recurse();
          wait();
          print "Seen child's exit\n"
        end
end
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