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 2ba9296..ad1a7c2 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -215,10 +215,10 @@
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 {
