From f1da2daf8325e437c66e2e0741ff6ce705382886 Mon Sep 17 00:00:00 2001
From: lilinzhe <reg@scsc.me>
Date: Wed, 5 Apr 2017 21:43:10 +0800
Subject: [PATCH] fix: channel race condition of ephemeral channel destroy &
 recreate

@see https://github.com/nsqio/go-nsq/issues/206
---
 nsqd/topic.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/nsqd/topic.go b/nsqd/topic.go
index 4c3ee2560..28cae7dfb 100644
--- a/nsqd/topic.go
+++ b/nsqd/topic.go
@@ -100,13 +100,23 @@ func (t *Topic) GetChannel(channelName string) *Channel {
 
 // this expects the caller to handle locking
 func (t *Topic) getOrCreateChannel(channelName string) (*Channel, bool) {
+	// block read when delete channel
+	t.RLock()
 	channel, ok := t.channelMap[channelName]
+	t.RUnlock()
 	if !ok {
 		deleteCallback := func(c *Channel) {
 			t.DeleteExistingChannel(c.name)
 		}
 		channel = NewChannel(t.name, channelName, t.ctx, deleteCallback)
+		t.Lock()
+		// avoid re-create channel
+		if oldchannel, ok := t.channelMap[channelName]; ok {
+			t.Unlock()
+			return oldchannel, false
+		}
 		t.channelMap[channelName] = channel
+		t.Unlock()
 		t.ctx.nsqd.logf("TOPIC(%s): new channel(%s)", t.name, channel.name)
 		return channel, true
 	}