From 78e3bb748b195a8a1902938101ea2c74bec4d120 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kr=C3=BCger?=
 <45282134+UweKrueger@users.noreply.github.com>
Date: Fri, 9 Apr 2021 09:57:41 +0200
Subject: [PATCH] sync: close channels atomically only once (#9645)

---
 vlib/sync/channels.v | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/vlib/sync/channels.v b/vlib/sync/channels.v
index cfabbb820d..bae6526fcd 100644
--- a/vlib/sync/channels.v
+++ b/vlib/sync/channels.v
@@ -138,7 +138,10 @@ fn new_channel_st(n u32, st u32) &Channel {
 }
 
 pub fn (mut ch Channel) close() {
-	C.atomic_store_u16(&ch.closed, 1)
+	open_val := u16(0)
+	if !C.atomic_compare_exchange_strong_u16(&ch.closed, &open_val, 1) {
+		return
+	}
 	mut nulladr := voidptr(0)
 	for !C.atomic_compare_exchange_weak_ptr(&ch.adr_written, &nulladr, voidptr(-1)) {
 		nulladr = voidptr(0)