Component-wide TransactionWriters (#1290)

* Offset updates take place using TransactionWriter

* Refactor TransactionWriter in current state server

* Refactor TransactionWriter in federation sender

* Refactor TransactionWriter in key server

* Refactor TransactionWriter in media API

* Refactor TransactionWriter in server key API

* Refactor TransactionWriter in sync API

* Refactor TransactionWriter in user API

* Fix deadlocking Sync API tests

* Un-deadlock device database

* Fix appservice API

* Rename TransactionWriters to Writers

* Move writers up a layer in sync API

* Document sqlutil.Writer interface

* Add note to Writer documentation

4 files changed, 34 insertions, 21 deletions

diff --git a/mediaapi/storage/sqlite3/media_repository_table.go b/mediaapi/storage/sqlite3/media_repository_table.go
index ff6ddf3d..dcc1b41e 100644
--- a/mediaapi/storage/sqlite3/media_repository_table.go
+++ b/mediaapi/storage/sqlite3/media_repository_table.go
@@ -62,14 +62,14 @@ SELECT content_type, file_size_bytes, creation_ts, upload_name, base64hash, user
 
 type mediaStatements struct {
 	db              *sql.DB
-	writer          sqlutil.TransactionWriter
+	writer          sqlutil.Writer
 	insertMediaStmt *sql.Stmt
 	selectMediaStmt *sql.Stmt
 }
 
-func (s *mediaStatements) prepare(db *sql.DB) (err error) {
+func (s *mediaStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 
 	_, err = db.Exec(mediaSchema)
 	if err != nil {
diff --git a/mediaapi/storage/sqlite3/sql.go b/mediaapi/storage/sqlite3/sql.go
index 9cd78b8e..245bd40c 100644
--- a/mediaapi/storage/sqlite3/sql.go
+++ b/mediaapi/storage/sqlite3/sql.go
@@ -17,6 +17,8 @@ package sqlite3
 
 import (
 	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 )
 
 type statements struct {
@@ -24,11 +26,11 @@ type statements struct {
 	thumbnail thumbnailStatements
 }
 
-func (s *statements) prepare(db *sql.DB) (err error) {
-	if err = s.media.prepare(db); err != nil {
+func (s *statements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
+	if err = s.media.prepare(db, writer); err != nil {
 		return
 	}
-	if err = s.thumbnail.prepare(db); err != nil {
+	if err = s.thumbnail.prepare(db, writer); err != nil {
 		return
 	}
 
diff --git a/mediaapi/storage/sqlite3/storage.go b/mediaapi/storage/sqlite3/storage.go
index a1e7fec7..d5c3031e 100644
--- a/mediaapi/storage/sqlite3/storage.go
+++ b/mediaapi/storage/sqlite3/storage.go
@@ -31,16 +31,19 @@ import (
 type Database struct {
 	statements statements
 	db         *sql.DB
+	writer     sqlutil.Writer
 }
 
 // Open opens a postgres database.
 func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
-	var d Database
+	d := Database{
+		writer: sqlutil.NewExclusiveWriter(),
+	}
 	var err error
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	if err = d.statements.prepare(d.db); err != nil {
+	if err = d.statements.prepare(d.db, d.writer); err != nil {
 		return nil, err
 	}
 	return &d, nil
diff --git a/mediaapi/storage/sqlite3/thumbnail_table.go b/mediaapi/storage/sqlite3/thumbnail_table.go
index 432a1590..06b056b6 100644
--- a/mediaapi/storage/sqlite3/thumbnail_table.go
+++ b/mediaapi/storage/sqlite3/thumbnail_table.go
@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/mediaapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -57,16 +58,20 @@ SELECT content_type, file_size_bytes, creation_ts, width, height, resize_method
 `
 
 type thumbnailStatements struct {
+	db                   *sql.DB
+	writer               sqlutil.Writer
 	insertThumbnailStmt  *sql.Stmt
 	selectThumbnailStmt  *sql.Stmt
 	selectThumbnailsStmt *sql.Stmt
 }
 
-func (s *thumbnailStatements) prepare(db *sql.DB) (err error) {
+func (s *thumbnailStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	_, err = db.Exec(thumbnailSchema)
 	if err != nil {
 		return
 	}
+	s.db = db
+	s.writer = writer
 
 	return statementList{
 		{&s.insertThumbnailStmt, insertThumbnailSQL},
@@ -79,18 +84,21 @@ func (s *thumbnailStatements) insertThumbnail(
 	ctx context.Context, thumbnailMetadata *types.ThumbnailMetadata,
 ) error {
 	thumbnailMetadata.MediaMetadata.CreationTimestamp = types.UnixMs(time.Now().UnixNano() / 1000000)
-	_, err := s.insertThumbnailStmt.ExecContext(
-		ctx,
-		thumbnailMetadata.MediaMetadata.MediaID,
-		thumbnailMetadata.MediaMetadata.Origin,
-		thumbnailMetadata.MediaMetadata.ContentType,
-		thumbnailMetadata.MediaMetadata.FileSizeBytes,
-		thumbnailMetadata.MediaMetadata.CreationTimestamp,
-		thumbnailMetadata.ThumbnailSize.Width,
-		thumbnailMetadata.ThumbnailSize.Height,
-		thumbnailMetadata.ThumbnailSize.ResizeMethod,
-	)
-	return err
+	return s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.insertThumbnailStmt)
+		_, err := stmt.ExecContext(
+			ctx,
+			thumbnailMetadata.MediaMetadata.MediaID,
+			thumbnailMetadata.MediaMetadata.Origin,
+			thumbnailMetadata.MediaMetadata.ContentType,
+			thumbnailMetadata.MediaMetadata.FileSizeBytes,
+			thumbnailMetadata.MediaMetadata.CreationTimestamp,
+			thumbnailMetadata.ThumbnailSize.Width,
+			thumbnailMetadata.ThumbnailSize.Height,
+			thumbnailMetadata.ThumbnailSize.ResizeMethod,
+		)
+		return err
+	})
 }
 
 func (s *thumbnailStatements) selectThumbnail(