From 55d412efa7f5a734d2f926e0c7c948f0ab4def21 Mon Sep 17 00:00:00 2001
From: gammazero <gammazero@users.noreply.github.com>
Date: Mon, 14 Jun 2021 14:03:52 -0700
Subject: [PATCH] Make close concurrent safe

---
 subscription.go | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/subscription.go b/subscription.go
index cf13622..0745f8d 100644
--- a/subscription.go
+++ b/subscription.go
@@ -2,6 +2,7 @@ package pubsub
 
 import (
 	"context"
+	"sync"
 )
 
 // Subscription handles the details of a particular Topic subscription.
@@ -10,9 +11,9 @@ type Subscription struct {
 	topic    string
 	ch       chan *Message
 	cancelCh chan<- *Subscription
-	closed   bool
 	ctx      context.Context
 	err      error
+	once     sync.Once
 }
 
 // Topic returns the topic string associated with the Subscription
@@ -44,8 +45,7 @@ func (sub *Subscription) Cancel() {
 }
 
 func (sub *Subscription) close() {
-	if !sub.closed {
+	sub.once.Do(func() {
 		close(sub.ch)
-		sub.closed = true
-	}
+	})
 }