From b540ef70b6c03cc0b6f76815a8bda05a04b97e9c Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Thu, 20 Aug 2020 15:57:04 +0100
Subject: [PATCH] Limit per-room mutexes to Postgres

---
 roomserver/internal/input.go          | 6 +++++-
 roomserver/storage/interface.go       | 2 ++
 roomserver/storage/shared/storage.go  | 4 ++++
 roomserver/storage/sqlite3/storage.go | 8 ++++++++
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/roomserver/internal/input.go b/roomserver/internal/input.go
index cbb61dfc1..567d8042f 100644
--- a/roomserver/internal/input.go
+++ b/roomserver/internal/input.go
@@ -73,7 +73,11 @@ func (r *RoomserverInternalAPI) InputRoomEvents(
 	response *api.InputRoomEventsResponse,
 ) (err error) {
 	for i, e := range request.InputRoomEvents {
-		mutex, _ := r.mutexes.LoadOrStore(e.Event.RoomID(), &sync.Mutex{})
+		roomID := e.Event.RoomID()
+		if !r.DB.SupportsConcurrentRoomInputs() {
+			roomID = "global"
+		}
+		mutex, _ := r.mutexes.LoadOrStore(roomID, &sync.Mutex{})
 		mutex.(*sync.Mutex).Lock()
 		if response.EventID, err = r.processRoomEvent(ctx, request.InputRoomEvents[i]); err != nil {
 			mutex.(*sync.Mutex).Unlock()
diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 988fc908d..545885f78 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -24,6 +24,8 @@ import (
 )
 
 type Database interface {
+	// Do we support processing input events for more than one room at a time?
+	SupportsConcurrentRoomInputs() bool
 	// Store the room state at an event in the database
 	AddState(
 		ctx context.Context,
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index aee3873a5..56c2b029d 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -44,6 +44,10 @@ type Database struct {
 	RedactionsTable     tables.Redactions
 }
 
+func (d *Database) SupportsConcurrentRoomInputs() bool {
+	return true
+}
+
 func (d *Database) EventTypeNIDs(
 	ctx context.Context, eventTypes []string,
 ) (map[string]types.EventTypeNID, error) {
diff --git a/roomserver/storage/sqlite3/storage.go b/roomserver/storage/sqlite3/storage.go
index 8e3af6b7a..874bbbc70 100644
--- a/roomserver/storage/sqlite3/storage.go
+++ b/roomserver/storage/sqlite3/storage.go
@@ -139,6 +139,14 @@ func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
 	return &d, nil
 }
 
+func (d *Database) SupportsConcurrentRoomInputs() bool {
+	// This isn't supported in SQLite mode yet because of issues with
+	// database locks.
+	// TODO: Look at this again - the problem is probably to do with
+	// the membership updaters and latest events updaters.
+	return false
+}
+
 func (d *Database) GetLatestEventsForUpdate(
 	ctx context.Context, roomNID types.RoomNID,
 ) (*shared.LatestEventsUpdater, error) {