cgosqlite: add more string interns, and optimize

cgosqlite/cgosqlite.go

@@ -253,11 +253,11 @@ func (stmt *Stmt) StartTimer() {
 }
 
 func (stmt *Stmt) ColumnDatabaseName(col int) string {
-	return C.GoString((*C.char)(unsafe.Pointer(C.sqlite3_column_database_name(stmt.stmt.ptr(), C.int(col)))))
+	return internStringFromCString(C.sqlite3_column_database_name(stmt.stmt.ptr(), C.int(col)))
 }
 
 func (stmt *Stmt) ColumnTableName(col int) string {
-	return C.GoString((*C.char)(unsafe.Pointer(C.sqlite3_column_table_name(stmt.stmt.ptr(), C.int(col)))))
+	return internStringFromCString(C.sqlite3_column_table_name(stmt.stmt.ptr(), C.int(col)))
 }
 
 func (stmt *Stmt) Step(colType []sqliteh.ColumnType) (row bool, err error) {
@@ -330,11 +330,7 @@ func (stmt *Stmt) BindParameterCount() int {
 }
 
 func (stmt *Stmt) BindParameterName(col int) string {
-	cstr := C.sqlite3_bind_parameter_name(stmt.stmt.ptr(), C.int(col))
-	if cstr == nil {
-		return ""
-	}
-	return C.GoString(cstr)
+	return internStringFromCString(C.sqlite3_bind_parameter_name(stmt.stmt.ptr(), C.int(col)))
 }
 
 func (stmt *Stmt) BindParameterIndex(name string) int {
@@ -357,7 +353,7 @@ func (stmt *Stmt) ColumnCount() int {
 }
 
 func (stmt *Stmt) ColumnName(col int) string {
-	return C.GoString(C.sqlite3_column_name(stmt.stmt.ptr(), C.int(col)))
+	return internStringFromCString(C.sqlite3_column_name(stmt.stmt.ptr(), C.int(col)))
 }
 
 func (stmt *Stmt) ColumnText(col int) string {
@@ -395,15 +391,15 @@ func (stmt *Stmt) ColumnDeclType(col int) string {
 	if cstr == nil {
 		return ""
 	}
-	clen := C.strlen(cstr)
-	b := (*[1 << 30]byte)(unsafe.Pointer(cstr))[0:clen]
+	bstr := (*byte)(unsafe.Pointer(cstr))
+	clen := findnull(bstr)
 	if stmt.db.declTypes == nil {
 		stmt.db.declTypes = make(map[string]string)
 	}
-	if res, found := stmt.db.declTypes[string(b)]; found {
+	if res, found := stmt.db.declTypes[unsafe.String(bstr, clen)]; found {
 		return res
 	}
-	res := string(b)
+	res := C.GoStringN(cstr, C.int(clen))
 	stmt.db.declTypes[res] = res
 	return res
 }
@@ -415,18 +411,29 @@ func errCode(code C.int) error { return sqliteh.CodeAsError(sqliteh.Code(code))
 // internCache contains interned strings.
 var internCache sync.Map // string => string (key == value)
 
-// stringFromBytes returns string(b), interned into a map forever. It's meant
+// internStringFromBytes returns string(b), interned into a map forever. It's meant
 // for use on hot, small strings from closed set (like database or table or
 // column names) where it doesn't matter if it leaks forever.
-func stringFromBytes(b []byte) string {
+func internStringFromBytes(b []byte) string {
 	if len(b) == 0 {
 		return ""
 	}
-	v, _ := internCache.Load(unsafe.String(&b[0], len(b)))
+	return internStringFromPtr((*C.char)(unsafe.Pointer(&b[0])), C.int(len(b)))
+}
+
+func internStringFromPtr(p *C.char, n C.int) string {
+	if n == 0 {
+		return ""
+	}
+	v, _ := internCache.Load(unsafe.String((*byte)(unsafe.Pointer(p)), int(n)))
 	if s, ok := v.(string); ok {
 		return s
 	}
-	s := string(b)
+	s := C.GoStringN(p, n)
 	internCache.Store(s, s)
 	return s
 }
+
+func internStringFromCString(p *C.char) string {
+	return internStringFromPtr(p, C.int(findnull((*byte)(unsafe.Pointer(p)))))
+}

cgosqlite/stubs.go

@@ -0,0 +1,10 @@
+package cgosqlite
+
+import _ "unsafe"
+
+// findnull exposes the runtime.findnull function to the cgosqlite package, this
+// is a wide instruction optimized page by page null byte search aka fast
+// strlen.
+//
+//go:linkname findnull runtime.findnull
+func findnull(*byte) int

cgosqlite/walcallback.go

@@ -20,7 +20,7 @@ func walCallbackGo(db *C.sqlite3, dbNameC *C.char, dbNameLen C.int, pages C.int)
 	}
 
 	dbNameB := unsafe.Slice((*byte)(unsafe.Pointer(dbNameC)), dbNameLen)
-	dbName := stringFromBytes(dbNameB)
+	dbName := internStringFromBytes(dbNameB)
 	hook(dbName, int(pages))
 	return C.int(0) // result's kinda useless
 }