From ab0e82d656921bb22a8ec7667ac721084061c0a2 Mon Sep 17 00:00:00 2001
From: Kyriakos Z <3829551+koox00@users.noreply.github.com>
Date: Thu, 19 Aug 2021 22:20:26 +0300
Subject: [PATCH] Fixes race condition in notification.go (#18226)

* Fixes race condition in notification.go

Appending is not thread safe, this commit makes followers a map
so we can add new followers from autofollow, and then adds those again
to followers.

* Fixes race condition
---
 app/notification.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/app/notification.go b/app/notification.go
index 9c8188555c..2bbb206e41 100644
--- a/app/notification.go
+++ b/app/notification.go
@@ -255,12 +255,12 @@ func (a *App) SendNotifications(post *model.Post, team *model.Team, channel *mod
 					return
 				}
 
+				followersMutex.Lock()
 				// add new followers to existing followers
 				if threadMembership.Following && !followers.Contains(userID) {
-					followersMutex.Lock()
 					followers = append(followers, userID)
-					followersMutex.Unlock()
 				}
+				followersMutex.Unlock()
 
 				membershipsMutex.Lock()
 				participantMemberships[userID] = threadMembership