how to use filehandle at MacOS 11？

why I can`t read the file in FileHandle? Mac OS 11 swift 5

Code Block swiftfile = try FileHandle(forReadingFrom: url)
        fileQueue = DispatchQueue(label: "model.source.opt.\(url.lastPathComponent)")
        var jsonData = Data()
        fileQueue.sync {
            if let lenthData = try? self.file.read(upToCount: 8) {
                var lenth = UInt64(lenthData[0])
                for i in 1 ..< lenthData.count {
                    lenth = lenth & (UInt64(lenthData[i] << (8 * i)))
                }
                print(lenth)/*print the 0*/
                self.file.waitForDataInBackgroundAndNotify()
                if let j = try? self.file.read(upToCount: Int(lenth)) {
                    jsonData = j
                }
                print(jsonData)/*print the 0 bytes*/
                self.firstFrameOffset = try! self.file.offset()
            }
        }