From 6b8a8294966316f6e044e78f76579a18a3e9c173 Mon Sep 17 00:00:00 2001
From: Ken Brown <kbrown@cornell.edu>
Date: Sat, 11 Jul 2020 14:52:55 -0400
Subject: [PATCH] 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.
---
 winsup/cygwin/fhandler_fifo.cc | 48 ++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 23 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
@@ -462,26 +462,10 @@ fhandler_fifo::fifo_reader_thread_func ()
 	take_ownership = true;
       else if (cur_owner != me)
 	idle = true;
-      if (take_ownership)
-	{
-	  if (!shared_fc_handler_updated ())
-	    {
-	      owner_unlock ();
-	      yield ();
-	      continue;
-	    }
-	  else
-	    {
-	      set_owner (me);
-	      set_pending_owner (null_fr_id);
-	      if (update_my_handlers () < 0)
-		api_fatal ("Can't update my handlers, %E");
-	      owner_found ();
-	      owner_unlock ();
-	      continue;
-	    }
-	}
-      else if (idle)
+      else
+	/* I'm the owner. */
+	goto owner_listen;
+      if (idle)
 	{
 	  owner_unlock ();
 	  HANDLE w[2] = { owner_needed_evt, cancel_evt };
@@ -495,9 +479,28 @@ fhandler_fifo::fifo_reader_thread_func ()
 	      api_fatal ("WFMO failed, %E");
 	    }
 	}
-      else
+      else if (take_ownership)
 	{
-	  /* I'm the owner */
+	  if (!shared_fc_handler_updated ())
+	    {
+	      owner_unlock ();
+	      if (IsEventSignalled (cancel_evt))
+		goto canceled;
+	      continue;
+	    }
+	  else
+	    {
+	      set_owner (me);
+	      set_pending_owner (null_fr_id);
+	      if (update_my_handlers () < 0)
+		api_fatal ("Can't update my handlers, %E");
+	      owner_found ();
+	      owner_unlock ();
+	      /* Fall through to owner_listen. */
+	    }
+	}
+
+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)