From e3340d61ec8d07a33f6391414367563265f9296f Mon Sep 17 00:00:00 2001
From: Joonas Myhrberg <joonas@myhrberg.email>
Date: Wed, 2 Aug 2023 21:57:54 +0300
Subject: [PATCH] Add global backfill lock

Ensures only a single channel is backfilled at once.
---
 backfill.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/backfill.go b/backfill.go
index 6e0f0a1..12025fc 100644
--- a/backfill.go
+++ b/backfill.go
@@ -6,6 +6,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"sort"
+	"sync"
 
 	"github.com/bwmarrin/discordgo"
 	"github.com/rs/zerolog"
@@ -16,6 +17,8 @@ import (
 	"go.mau.fi/mautrix-discord/database"
 )
 
+var globalBackfillLock sync.Mutex
+
 func (portal *Portal) forwardBackfillInitial(source *User, thread *Thread) {
 	log := portal.log
 	defer func() {
@@ -27,6 +30,9 @@ func (portal *Portal) forwardBackfillInitial(source *User, thread *Thread) {
 		panic("forwardBackfillInitial() called without locking forwardBackfillLock")
 	}
 
+	globalBackfillLock.Lock()
+	defer globalBackfillLock.Unlock()
+
 	limit := portal.bridge.Config.Bridge.Backfill.Limits.Initial.Channel
 	if portal.GuildID == "" {
 		limit = portal.bridge.Config.Bridge.Backfill.Limits.Initial.DM
@@ -78,6 +84,9 @@ func (portal *Portal) ForwardBackfillMissed(source *User, serverLastMessageID st
 	portal.forwardBackfillLock.Lock()
 	defer portal.forwardBackfillLock.Unlock()
 
+	globalBackfillLock.Lock()
+	defer globalBackfillLock.Unlock()
+
 	var lastMessage *database.Message
 	if thread != nil {
 		lastMessage = portal.bridge.DB.Message.GetLastInThread(portal.Key, thread.ID)