Try to avoid database locks

eduserver/cache/cache.go

@@ -115,9 +115,9 @@ func (t *EDUCache) AddTypingUser(
 func (t *EDUCache) AddSendToDeviceMessage() int64 {
 	t.Lock()
 	defer t.Unlock()
-
+	r := t.latestSyncPosition
 	t.latestSyncPosition++
-	return t.latestSyncPosition - 1
+	return r
 }
 
 // addUser with mutex lock & replace the previous timer.

internal/sql.go

@@ -19,6 +19,8 @@ import (
 	"fmt"
 	"runtime"
 	"time"
+
+	"go.uber.org/atomic"
 )
 
 // A Transaction is something that can be committed or rolledback.
@@ -107,3 +109,44 @@ type DbProperties interface {
 	MaxOpenConns() int
 	ConnMaxLifetime() time.Duration
 }
+
+type TransactionWriter struct {
+	running atomic.Bool
+	todo    chan transactionWriterTask
+}
+
+type transactionWriterTask struct {
+	db   *sql.DB
+	f    func(txn *sql.Tx)
+	wait chan struct{}
+}
+
+func (w *TransactionWriter) Do(db *sql.DB, f func(txn *sql.Tx)) {
+	if w.todo == nil {
+		w.todo = make(chan transactionWriterTask)
+	}
+	if !w.running.Load() {
+		go w.run()
+	}
+	task := transactionWriterTask{
+		db:   db,
+		f:    f,
+		wait: make(chan struct{}),
+	}
+	w.todo <- task
+	<-task.wait
+}
+
+func (w *TransactionWriter) run() {
+	if !w.running.CAS(false, true) {
+		return
+	}
+	defer w.running.Store(false)
+	for task := range w.todo {
+		_ = WithTransaction(task.db, func(txn *sql.Tx) error {
+			task.f(txn)
+			return nil
+		})
+		close(task.wait)
+	}
+}

syncapi/consumers/eduserver_sendtodevice.go

@@ -25,6 +25,7 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/sync"
 	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	log "github.com/sirupsen/logrus"
 )
@@ -33,6 +34,7 @@ import (
 type OutputSendToDeviceEventConsumer struct {
 	sendToDeviceConsumer *internal.ContinualConsumer
 	db                   storage.Database
+	serverName           gomatrixserverlib.ServerName // our server name
 	notifier             *sync.Notifier
 }
 
@@ -54,6 +56,7 @@ func NewOutputSendToDeviceEventConsumer(
 	s := &OutputSendToDeviceEventConsumer{
 		sendToDeviceConsumer: &consumer,
 		db:                   store,
+		serverName:           cfg.Matrix.ServerName,
 		notifier:             n,
 	}
 
@@ -75,6 +78,14 @@ func (s *OutputSendToDeviceEventConsumer) onMessage(msg *sarama.ConsumerMessage)
 		return err
 	}
 
+	_, domain, err := gomatrixserverlib.SplitID('@', output.UserID)
+	if err != nil {
+		return err
+	}
+	if domain != s.serverName {
+		return nil
+	}
+
 	util.GetLogger(context.TODO()).WithFields(log.Fields{
 		"sender":     output.Sender,
 		"user_id":    output.UserID,

syncapi/storage/shared/syncserver.go

@@ -28,6 +28,7 @@ type Database struct {
 	CurrentRoomState    tables.CurrentRoomState
 	BackwardExtremities tables.BackwardsExtremities
 	SendToDevice        tables.SendToDevice
+	SendToDeviceWriter  internal.TransactionWriter
 	EDUCache            *cache.EDUCache
 }
 
@@ -1045,9 +1046,13 @@ func (d *Database) StoreNewSendForDeviceMessage(
 	if err != nil {
 		return 0, err
 	}
+	// Delegate the database write task to the SendToDeviceWriter. It'll guarantee
+	// that we don't lock the table for writes in more than one place.
+	d.SendToDeviceWriter.Do(d.DB, func(txn *sql.Tx) {
 		err = d.AddSendToDeviceEvent(
-		ctx, nil, userID, deviceID, string(j),
+			ctx, txn, userID, deviceID, string(j),
 		)
+	})
 	if err != nil {
 		return 0, err
 	}
@@ -1059,11 +1064,10 @@ func (d *Database) SendToDeviceUpdatesForSync(
 	userID, deviceID string,
 	token types.StreamingToken,
 ) (events []types.SendToDeviceEvent, err error) {
-	err = internal.WithTransaction(d.DB, func(txn *sql.Tx) error {
 	// First of all, get our send-to-device updates for this user.
-		events, err = d.SendToDevice.SelectSendToDeviceMessages(ctx, txn, userID, deviceID)
+	events, err = d.SendToDevice.SelectSendToDeviceMessages(ctx, nil, userID, deviceID)
 	if err != nil {
-			return fmt.Errorf("d.SendToDevice.SelectSendToDeviceMessages: %w", err)
+		return nil, fmt.Errorf("d.SendToDevice.SelectSendToDeviceMessages: %w", err)
 	}
 
 	// Start by cleaning up any send-to-device messages that have older sent-by-tokens.
@@ -1083,18 +1087,25 @@ func (d *Database) SendToDeviceUpdatesForSync(
 		}
 	}
 
+	// If we need to write to the database then we'll ask the SendToDeviceWriter to
+	// do that for us. It'll guarantee that we don't lock the table for writes in
+	// more than one place.
+	if len(toUpdate) > 0 || len(toDelete) > 0 {
+		d.SendToDeviceWriter.Do(d.DB, func(txn *sql.Tx) {
 			// Delete any send-to-device messages marked for deletion.
-		if err := d.SendToDevice.DeleteSendToDeviceMessages(ctx, txn, toDelete); err != nil {
+			if e := d.SendToDevice.DeleteSendToDeviceMessages(ctx, txn, toDelete); e != nil {
-			return fmt.Errorf("d.SendToDevice.DeleteSendToDeviceMessages: %w", err)
+				err = fmt.Errorf("d.SendToDevice.DeleteSendToDeviceMessages: %w", e)
+				return
 			}
 
 			// Now update any outstanding send-to-device messages with the new sync token.
-		if err := d.SendToDevice.UpdateSentSendToDeviceMessages(ctx, txn, token.String(), toUpdate); err != nil {
+			if e := d.SendToDevice.UpdateSentSendToDeviceMessages(ctx, txn, token.String(), toUpdate); e != nil {
-			return fmt.Errorf("d.SendToDevice.UpdateSentSendToDeviceMessages: %w", err)
+				err = fmt.Errorf("d.SendToDevice.UpdateSentSendToDeviceMessages: %w", err)
+				return
+			}
+		})
 	}
 
-		return nil
-	})
 	return
 }
 

sytest-whitelist

@@ -289,3 +289,9 @@ Existing members see new members' join events
 Inbound federation can receive events
 Inbound federation can receive redacted events
 Can logout current device
+Can send a message directly to a device using PUT /sendToDevice
+Can recv a device message using /sync
+Can send a to-device message to two users which both receive it using /sync
+Can recv device messages until they are acknowledged
+Device messages wake up /sync
+Device messages over federation wake up /sync