From 0c5963626c45b2971fce766781adcbaf7e9e83ae Mon Sep 17 00:00:00 2001
From: kenwschen <ken00535@gmail.com>
Date: Mon, 7 Jun 2021 23:35:31 +0800
Subject: [PATCH] fix(event_bus): panic if multiple goroutine call publish and
 then wait

because of wg's counter can't be a negative number, if call Wait() and then call Add(1) before
Wait() complete, it will throw panic "WaitGroup is reused before previous Wait has returned". so add
a mutex to prevent this issue. for more detail, see:
https://stackoverflow.com/questions/48351816/waitgroup-is-reused-before-previous-wait-unknown-reason
---
 event_bus.go      |  2 ++
 event_bus_test.go | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/event_bus.go b/event_bus.go
index dedc7fd..bec4eb9 100644
--- a/event_bus.go
+++ b/event_bus.go
@@ -211,5 +211,7 @@ func (bus *EventBus) setUpPublish(callback *eventHandler, args ...interface{}) [
 
 // WaitAsync waits for all async callbacks to complete
 func (bus *EventBus) WaitAsync() {
+	bus.lock.Lock()
+	defer bus.lock.Unlock()
 	bus.wg.Wait()
 }
diff --git a/event_bus_test.go b/event_bus_test.go
index 0cdb579..55f4050 100644
--- a/event_bus_test.go
+++ b/event_bus_test.go
@@ -188,3 +188,18 @@ func TestSubscribeAsync(t *testing.T) {
 	//	t.Fail()
 	//}
 }
+
+func TestSubscribeAsyncWithMultipleGoroutine(t *testing.T) {
+	for i := 0; i < 100; i++ {
+		bus := New()
+		bus.SubscribeAsync("topic", func() {
+			time.Sleep(time.Millisecond)
+		}, false)
+		bus.Publish("topic")
+		go func() {
+			time.Sleep(time.Millisecond)
+			bus.Publish("topic")
+		}()
+		bus.WaitAsync()
+	}
+}