From 4380fa6d99284c03e471bafcb1be2db83b225af4 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Mon, 24 Dec 2012 21:06:57 +0400
Subject: [PATCH] runtime: diagnose double wakeup on Note Double wakeup is
 prohibited by the Note interface and checked in lock_sema.c.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6976054
---
 src/pkg/runtime/lock_futex.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/pkg/runtime/lock_futex.c b/src/pkg/runtime/lock_futex.c
index b4465bff18d..9b1f5f6db43 100644
--- a/src/pkg/runtime/lock_futex.c
+++ b/src/pkg/runtime/lock_futex.c
@@ -111,7 +111,8 @@ runtime·noteclear(Note *n)
 void
 runtime·notewakeup(Note *n)
 {
-	runtime·xchg(&n->key, 1);
+	if(runtime·xchg(&n->key, 1))
+		runtime·throw("notewakeup - double wakeup");
 	runtime·futexwakeup(&n->key, 1);
 }