[newlib-cygwin] Cygwin: FIFO: fix the error checking in raw_read

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=513f050cbf1b9e1ac40e08d258e496272bde920f

commit 513f050cbf1b9e1ac40e08d258e496272bde920f
Author: Ken Brown <kbr...@cornell.edu>
Date:   Sun Apr 14 19:15:58 2019 +0000

    Cygwin: FIFO: fix the error checking in raw_read
    
    If the pipe is empty, we can get either ERROR_NO_DATA or
    ERROR_PIPE_LISTENING.

Diff:
---
 winsup/cygwin/fhandler_fifo.cc | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
index 764420f..2da579b 100644
--- a/winsup/cygwin/fhandler_fifo.cc
+++ b/winsup/cygwin/fhandler_fifo.cc
@@ -749,19 +749,16 @@ fhandler_fifo::raw_read (void *in_ptr, size_t& len)
                fifo_client_unlock ();
                return;
              }
-           /* In the duplex case with no data, we seem to get nread
-              == -1 with ERROR_PIPE_LISTENING on the first attempt to
-              read from the duplex pipe (fc_handler[0]), and nread == 0
-              on subsequent attempts. */
+           /* If the pipe is empty, we usually get nread == -1 with
+              ERROR_NO_DATA or ERROR_PIPE_LISTENING.  An exception is
+              that in the duplex case we may get nread == 0 when we
+              attempt to read from the duplex pipe (fc_handler[0]). */
            else if (nread < 0)
              switch (GetLastError ())
                {
                case ERROR_NO_DATA:
-                 break;
                case ERROR_PIPE_LISTENING:
-                 if (_duplexer && i == 0)
-                   break;
-                 /* Fall through. */
+                 break;
                default:
                  fifo_client_unlock ();
                  goto errout;