remove superfluous use of runtime.SetFinalizer on SQLiteRows

sqlite3.go

@@ -381,7 +381,7 @@ type SQLiteStmt struct {
 	s      *C.sqlite3_stmt
 	t      string
 	closed bool
-	cls    bool
+	cls    bool // True if the statement was created by SQLiteConn.Query
 }
 
 // SQLiteResult implements sql.Result.
@@ -393,12 +393,12 @@ type SQLiteResult struct {
 // SQLiteRows implements driver.Rows.
 type SQLiteRows struct {
 	s        *SQLiteStmt
-	nc       int
+	nc       int32 // Number of columns
+	cls      bool  // True if we need to close the parent statement in Close
 	cols     []string
 	decltype []string
-	cls      bool
-	closed   bool
 	ctx      context.Context // no better alternative to pass context into Next() method
+	closemu  sync.Mutex
 }
 
 type functionInfo struct {
@@ -2008,14 +2008,12 @@ func (s *SQLiteStmt) query(ctx context.Context, args []driver.NamedValue) (drive
 
 	rows := &SQLiteRows{
 		s:        s,
-		nc:       int(C.sqlite3_column_count(s.s)),
+		nc:       int32(C.sqlite3_column_count(s.s)),
+		cls:      s.cls,
 		cols:     nil,
 		decltype: nil,
-		cls:      s.cls,
-		closed:   false,
 		ctx:      ctx,
 	}
-	runtime.SetFinalizer(rows, (*SQLiteRows).Close)
 
 	return rows, nil
 }
@@ -2112,34 +2110,38 @@ func (s *SQLiteStmt) Readonly() bool {
 
 // Close the rows.
 func (rc *SQLiteRows) Close() error {
-	rc.s.mu.Lock()
-	if rc.s.closed || rc.closed {
-		rc.s.mu.Unlock()
+	rc.closemu.Lock()
+	defer rc.closemu.Unlock()
+	s := rc.s
+	if s == nil {
+		return nil
+	}
+	rc.s = nil // remove reference to SQLiteStmt
+	s.mu.Lock()
+	if s.closed {
+		s.mu.Unlock()
 		return nil
 	}
-	rc.closed = true
 	if rc.cls {
-		rc.s.mu.Unlock()
-		return rc.s.Close()
+		s.mu.Unlock()
+		return s.Close()
 	}
-	rv := C.sqlite3_reset(rc.s.s)
+	rv := C.sqlite3_reset(s.s)
 	if rv != C.SQLITE_OK {
-		rc.s.mu.Unlock()
-		return rc.s.c.lastError()
+		s.mu.Unlock()
+		return s.c.lastError()
 	}
-	rc.s.mu.Unlock()
-	rc.s = nil
-	runtime.SetFinalizer(rc, nil)
+	s.mu.Unlock()
 	return nil
 }
 
 // Columns return column names.
 func (rc *SQLiteRows) Columns() []string {
 	rc.s.mu.Lock()
 	defer rc.s.mu.Unlock()
-	if rc.s.s != nil && rc.nc != len(rc.cols) {
+	if rc.s.s != nil && int(rc.nc) != len(rc.cols) {
 		rc.cols = make([]string, rc.nc)
-		for i := 0; i < rc.nc; i++ {
+		for i := 0; i < int(rc.nc); i++ {
 			rc.cols[i] = C.GoString(C.sqlite3_column_name(rc.s.s, C.int(i)))
 		}
 	}
@@ -2149,7 +2151,7 @@ func (rc *SQLiteRows) Columns() []string {
 func (rc *SQLiteRows) declTypes() []string {
 	if rc.s.s != nil && rc.decltype == nil {
 		rc.decltype = make([]string, rc.nc)
-		for i := 0; i < rc.nc; i++ {
+		for i := 0; i < int(rc.nc); i++ {
 			rc.decltype[i] = strings.ToLower(C.GoString(C.sqlite3_column_decltype(rc.s.s, C.int(i))))
 		}
 	}

sqlite3_test.go

@@ -2111,6 +2111,7 @@ var benchmarks = []testing.InternalBenchmark{
 	{Name: "BenchmarkStmt", F: benchmarkStmt},
 	{Name: "BenchmarkRows", F: benchmarkRows},
 	{Name: "BenchmarkStmtRows", F: benchmarkStmtRows},
+	{Name: "BenchmarkQueryParallel", F: benchmarkQueryParallel},
 }
 
 func (db *TestDB) mustExec(sql string, args ...any) sql.Result {
@@ -2568,3 +2569,20 @@ func benchmarkStmtRows(b *testing.B) {
 		}
 	}
 }
+
+func benchmarkQueryParallel(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		db, err := sql.Open("sqlite3", ":memory:")
+		if err != nil {
+			panic(err)
+		}
+		db.SetMaxOpenConns(runtime.NumCPU())
+		defer db.Close()
+		var i int64
+		for pb.Next() {
+			if err := db.QueryRow("SELECT 1, 2, 3, 4").Scan(&i, &i, &i, &i); err != nil {
+				panic(err)
+			}
+		}
+	})
+}