The buffer clearing function isn't working on my device.

[JingKun-Jiang]

When I call flush() there still seems to be data in the buffer.
当我调用了flush()之后缓冲区中貌似仍有数据。

QQ2025104-20246.mp4

In the video, I send a variable q0 to the device through the serial port, which automatically increases by 1 every second. When I close the program with CTRL+C and wait for a while before reopening it, I can still see the variable value during the period when the program was closed (increasing at a speed of about half a second until it catches up with the actual value sent by the serial port at this time and then returns to increasing by one second).
在视频中我通过串口向设备发送每秒自动＋1的变量q0，在我使用CTRL+C关闭程序并等待一段时间后再打开程序，仍能看到关闭程序期间的变量值（以半秒左右的速度递增直到追赶上此时串口发送的实际值后恢复到一秒递增）。