runtime: refine code reducing indents in netpollBreak()

Change-Id: I2d1528910cb3660344c7a664d6f32306defe75d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/419321
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>

1 files changed, 15 insertions, 12 deletions

diff --git a/src/runtime/netpoll_kqueue.go b/src/runtime/netpoll_kqueue.go
index 1694753b6f..78d1663ad9 100644
--- a/src/runtime/netpoll_kqueue.go
+++ b/src/runtime/netpoll_kqueue.go
@@ -83,19 +83,22 @@ func netpollarm(pd *pollDesc, mode int) {
 
 // netpollBreak interrupts a kevent.
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		for {
-			var b byte
-			n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
-			if n == 1 || n == -_EAGAIN {
-				break
-			}
-			if n == -_EINTR {
-				continue
-			}
-			println("runtime: netpollBreak write failed with", -n)
-			throw("runtime: netpollBreak write failed")
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
+	}
+
+	for {
+		var b byte
+		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
+		if n == 1 || n == -_EAGAIN {
+			break
+		}
+		if n == -_EINTR {
+			continue
 		}
+		println("runtime: netpollBreak write failed with", -n)
+		throw("runtime: netpollBreak write failed")
 	}
 }