[newlib-cygwin] Cygwin: FIFO: improve taking ownership in fifo_reader_thread

[Ken Brown <kbrown@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=6b8a8294966316f6e044e78f76579a18a3e9c173

commit 6b8a8294966316f6e044e78f76579a18a3e9c173
Author: Ken Brown <kbrown@cornell.edu>
Date:   Sat Jul 11 14:52:55 2020 -0400

    Cygwin: FIFO: improve taking ownership in fifo_reader_thread
    
    When a reader takes ownership in fifo_reader_thread, it now goes
    directly to the part of the main loop that listens for a connection.
    Previously it went back to the beginning of the loop.
    
    Also, if the reader has to delay taking ownership because the previous
    owner has not finished updating the shared fifo_client handlers, it
    now checks to see if cancel_evt has been set.  Previously it might
    have had to spin its wheels unnecessarily only to eventually find that
    its thread had been canceled.

Diff:
---
 winsup/cygwin/fhandler_fifo.cc | 44 ++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
index afe21a468..1fb319fcf 100644
--- a/winsup/cygwin/fhandler_fifo.cc
+++ b/winsup/cygwin/fhandler_fifo.cc
@@ -462,12 +462,30 @@ fhandler_fifo::fifo_reader_thread_func ()
 	take_ownership = true;
       else if (cur_owner != me)
 	idle = true;
-      if (take_ownership)
+      else
+	/* I'm the owner. */
+	goto owner_listen;
+      if (idle)
+	{
+	  owner_unlock ();
+	  HANDLE w[2] = { owner_needed_evt, cancel_evt };
+	  switch (WaitForMultipleObjects (2, w, false, INFINITE))
+	    {
+	    case WAIT_OBJECT_0:
+	      continue;
+	    case WAIT_OBJECT_0 + 1:
+	      goto canceled;
+	    default:
+	      api_fatal ("WFMO failed, %E");
+	    }
+	}
+      else if (take_ownership)
 	{
 	  if (!shared_fc_handler_updated ())
 	    {
 	      owner_unlock ();
-	      yield ();
+	      if (IsEventSignalled (cancel_evt))
+		goto canceled;
 	      continue;
 	    }
 	  else
@@ -478,26 +496,11 @@ fhandler_fifo::fifo_reader_thread_func ()
 		api_fatal ("Can't update my handlers, %E");
 	      owner_found ();
 	      owner_unlock ();
-	      continue;
+	      /* Fall through to owner_listen. */
 	    }
 	}
-      else if (idle)
-	{
-	  owner_unlock ();
-	  HANDLE w[2] = { owner_needed_evt, cancel_evt };
-	  switch (WaitForMultipleObjects (2, w, false, INFINITE))
-	    {
-	    case WAIT_OBJECT_0:
-	      continue;
-	    case WAIT_OBJECT_0 + 1:
-	      goto canceled;
-	    default:
-	      api_fatal ("WFMO failed, %E");
-	    }
-	}
-      else
-	{
-	  /* I'm the owner */
+
+owner_listen:
 	  fifo_client_lock ();
 	  cleanup_handlers ();
 	  if (add_client_handler () < 0)
@@ -590,7 +593,6 @@ fhandler_fifo::fifo_reader_thread_func ()
 	  fifo_client_unlock ();
 	  if (cancel)
 	    goto canceled;
-	}
     }
 canceled:
   if (conn_evt)