From: Ian Lance Taylor <iant@golang.org>
Date: Sat, 12 Mar 2011 02:01:28 +0000 (-0800)
Subject: net: don't loop to drain wakeup pipe.
X-Git-Tag: weekly.2011-03-15~29
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c01238a571769f12a9c2bb971d26fe27c4158530;p=gostls13.git

net: don't loop to drain wakeup pipe.

The loop always makes an extra system call.  It only makes a
difference if more than 100 goroutines started waiting for
something to happen on a network file descriptor since the
last time the pipe was drained, which is unlikely since we
will be woken up the first time a goroutine starts waiting.
If we don't drain the pipe this time, we'll be woken up again
right away and can drain again.

R=rsc
CC=golang-dev
https://golang.org/cl/4275042
---

diff --git a/src/pkg/net/fd.go b/src/pkg/net/fd.go
index 2ba9296f31..ad1a7c29a9 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -215,10 +215,10 @@ func (s *pollServer) Run() {
 			continue
 		}
 		if fd == s.pr.Fd() {
-			// Drain our wakeup pipe.
-			for nn, _ := s.pr.Read(scratch[0:]); nn > 0; {
-				nn, _ = s.pr.Read(scratch[0:])
-			}
+			// Drain our wakeup pipe (we could loop here,
+			// but it's unlikely that there are more than
+			// len(scratch) wakeup calls).
+			s.pr.Read(scratch[0:])
 			// Read from channels
 		Update:
 			for {