[newlib-cygwin] Cygwin: FIFO: don't read from pipes that are closing

[Ken Brown <kbrown@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=251624a3529c3d0d3d9cdb5fbaf4c3e9b079c894

commit 251624a3529c3d0d3d9cdb5fbaf4c3e9b079c894
Author: Ken Brown <kbrown@cornell.edu>
Date:   Mon Aug 3 09:35:00 2020 -0400

    Cygwin: FIFO: don't read from pipes that are closing
    
    Don't try to read from fifo_client_handlers that are in the fc_closing
    state.  Experiments have shown that this always yields
    STATUS_PIPE_BROKEN, so it just wastes a Windows system call.
    
    Re-order the values in enum fifo_client_connect_state to reflect the
    new status of fc_closing.

Diff:
---
 winsup/cygwin/fhandler.h       | 9 +--------
 winsup/cygwin/fhandler_fifo.cc | 6 +++---
 winsup/cygwin/select.cc        | 2 +-
 3 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index f64eabda4..40e201b0f 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -1276,20 +1276,13 @@ public:
 
 #define CYGWIN_FIFO_PIPE_NAME_LEN     47
 
-/* We view the fc_closing state as borderline between open and closed
-   for a writer at the other end of a fifo_client_handler.
-
-   We still attempt to read from the writer when the handler is in
-   this state, and we don't declare a reader to be at EOF if there's a
-   handler in this state.  But the existence of a handler in this
-   state is not sufficient to unblock a reader trying to open. */
 enum fifo_client_connect_state
 {
   fc_unknown,
   fc_error,
   fc_disconnected,
-  fc_listening,
   fc_closing,
+  fc_listening,
   fc_connected,
   fc_input_avail,
 };
diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
index c816c692a..1e1140f53 100644
--- a/winsup/cygwin/fhandler_fifo.cc
+++ b/winsup/cygwin/fhandler_fifo.cc
@@ -365,7 +365,7 @@ fhandler_fifo::cleanup_handlers ()
 
   while (i < nhandlers)
     {
-      if (fc_handler[i].get_state () < fc_closing)
+      if (fc_handler[i].get_state () < fc_connected)
 	delete_client_handler (i);
       else
 	i++;
@@ -1280,7 +1280,7 @@ fhandler_fifo::raw_read (void *in_ptr, size_t& len)
       for (j = 0; j < nhandlers; j++)
 	if (fc_handler[j].last_read)
 	  break;
-      if (j < nhandlers && fc_handler[j].get_state () >= fc_closing)
+      if (j < nhandlers && fc_handler[j].get_state () >= fc_connected)
 	{
 	  NTSTATUS status;
 	  IO_STATUS_BLOCK io;
@@ -1315,7 +1315,7 @@ fhandler_fifo::raw_read (void *in_ptr, size_t& len)
 
       /* Second pass. */
       for (int i = 0; i < nhandlers; i++)
-	if (fc_handler[i].get_state () >= fc_closing)
+	if (fc_handler[i].get_state () >= fc_connected)
 	  {
 	    NTSTATUS status;
 	    IO_STATUS_BLOCK io;
diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index 0c94f6c45..9ee305f64 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -878,7 +878,7 @@ peek_fifo (select_record *s, bool from_select)
 	{
 	  fifo_client_handler &fc = fh->get_fc_handler (i);
 	  fc.query_and_set_state ();
-	  if (fc.get_state () >= fc_closing)
+	  if (fc.get_state () >= fc_connected)
 	    {
 	      nconnected++;
 	      if (fc.get_state () == fc_input_avail)