Writer exclusivity for SQLite

internal/storage/sqlite3/sqlite3.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	_ "github.com/mattn/go-sqlite3"
+	"go.uber.org/atomic"
 )
 
 type SQLite3Storage struct {
@@ -12,6 +13,7 @@ type SQLite3Storage struct {
 	*TableMailboxes
 	*TableMails
 	*TableQueue
+	writer *Writer
 }
 
 func NewSQLite3StorageStorage(filename string) (*SQLite3Storage, error) {
@@ -19,22 +21,81 @@ func NewSQLite3StorageStorage(filename string) (*SQLite3Storage, error) {
 	if err != nil {
 		return nil, fmt.Errorf("sql.Open: %w", err)
 	}
-	s := &SQLite3Storage{}
-	s.TableConfig, err = NewTableConfig(db)
+	s := &SQLite3Storage{
+		writer: &Writer{
+			todo: make(chan writerTask),
+		},
+	}
+	s.TableConfig, err = NewTableConfig(db, s.writer)
 	if err != nil {
 		return nil, fmt.Errorf("NewTableConfig: %w", err)
 	}
-	s.TableMailboxes, err = NewTableMailboxes(db)
+	s.TableMailboxes, err = NewTableMailboxes(db, s.writer)
 	if err != nil {
 		return nil, fmt.Errorf("NewTableMailboxes: %w", err)
 	}
-	s.TableMails, err = NewTableMails(db)
+	s.TableMails, err = NewTableMails(db, s.writer)
 	if err != nil {
 		return nil, fmt.Errorf("NewTableMails: %w", err)
 	}
-	s.TableQueue, err = NewTableQueue(db)
+	s.TableQueue, err = NewTableQueue(db, s.writer)
 	if err != nil {
 		return nil, fmt.Errorf("NewTableQueue: %w", err)
 	}
 	return s, nil
 }
+
+type Writer struct {
+	running atomic.Bool
+	todo    chan writerTask
+}
+
+type writerTask struct {
+	db   *sql.DB
+	txn  *sql.Tx
+	f    func(txn *sql.Tx) error
+	wait chan error
+}
+
+func (w *Writer) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error {
+	if !w.running.Load() {
+		go w.run()
+	}
+	task := writerTask{
+		db:   db,
+		txn:  txn,
+		f:    f,
+		wait: make(chan error, 1),
+	}
+	w.todo <- task
+	return <-task.wait
+}
+
+func (w *Writer) run() {
+	if !w.running.CAS(false, true) {
+		return
+	}
+	defer w.running.Store(false)
+	for task := range w.todo {
+		if task.db != nil && task.txn != nil {
+			task.wait <- task.f(task.txn)
+		} else if task.db != nil && task.txn == nil {
+			func() {
+				txn, err := task.db.Begin()
+				if err != nil {
+					return
+				}
+				err = task.f(txn)
+				task.wait <- err
+				if err == nil {
+					_ = txn.Commit()
+				} else {
+					_ = txn.Rollback()
+				}
+			}()
+		} else {
+			task.wait <- task.f(nil)
+		}
+		close(task.wait)
+	}
+}