From b907cf21790b8ff5d2675f2859bcbdbf51ca5ec1 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Tue, 3 Dec 2019 14:05:08 +0200
Subject: [PATCH] sync/waitgroup: force sleeping for 1ms

fixes issues #2874 and #2961
---
 examples/news_fetcher.v | 2 +-
 vlib/sync/waitgroup.v   | 9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/examples/news_fetcher.v b/examples/news_fetcher.v
index dce80a2487..5b390a62ff 100644
--- a/examples/news_fetcher.v
+++ b/examples/news_fetcher.v
@@ -67,7 +67,7 @@ fn main() {
 	
 	wg := sync.new_waitgroup()
 	mtx := sync.new_mutex()
-	mut fetcher := &Fetcher{ids: ids}
+	mut fetcher := &Fetcher{ids: ids mu: 0 wg: 0}
 	fetcher.mu = &mtx
 	fetcher.wg = &wg
 	fetcher.wg.add(ids.len)
diff --git a/vlib/sync/waitgroup.v b/vlib/sync/waitgroup.v
index 307192e824..35a8f358a6 100644
--- a/vlib/sync/waitgroup.v
+++ b/vlib/sync/waitgroup.v
@@ -32,7 +32,12 @@ pub fn (wg mut WaitGroup) done() {
 
 pub fn (wg mut WaitGroup) wait() {
 	for wg.active > 0 {
-		// waiting
+		// Do not remove this, busy empty loops are optimized
+		// with -prod by some compilers, see issue #2874
+		$if windows {
+			C.Sleep(1)
+		} $else {
+			C.usleep(1000)
+		}
 	}
 }
-