Serial Port is not disposed correctly during a flutter hot restart

[bryceremick]

Anytime I do a hot restart on my flutter app after the port has been initialized, I get this error:

Unhandled Exception: SerialPortError: Device or resource busy, errno = 16

Basically my app runs through this initialization process during every hot restart:

1. Close/Dispose the port if it already exists
2. Create new SerialPort instance
3. OpenReadWrite
4. Set Baud Rate
5. Create new SerialPortReader instance
6. Listen to data

I get this error at step 3 after a hot restart.

My guess is that the port is not disposed correctly and when a new port gets opened for read/write the OS throws this error because the old port still exists in memory.

This is on Android 7.1 btw.

Any suggestions on how to solve this?

Thanks

[saguado69]

Same for me, sorry @bryceremick how do you run the package under Android? It does not work for me, I always have an issue related to permissions.

Thanks for any help.

[hareendranmg]

Hi @bryceremick, do you find any solution? I also getting this error in ubuntu.

[bryceremick]

@hareendranmg I have not found any solution for this yet, unfortunately. Hot reload is working for me, but not hot restart.

[evanwsu]

I believe the reason for this issue is that Flutter performs a hot restart, which restarts the entire application, causing the SerialPort instance to be garbage-collected, but the SerialPort object associated with the native object is not properly disposed. I attempted to call serialPort.dispose() in relevant lifecycle methods, but it seems that hot restart does not trigger these lifecycle methods.

[NickNevzorov]

Same for windows. After hot restart serialPort.dispose() is not called and no way to reopen port

[shingohu]

I have solved this problem. You can save the address of the last opened serial port. When hot restart occurs, check for any serial port addresses that have not been properly closed in the main function. If they exist, create a SerialPort by constructing the SerialPort. freeAddress method, then close and dispose of them

[vigorox]

I have solved this problem. You can save the address of the last opened serial port. When hot restart occurs, check for any serial port addresses that have not been properly closed in the main function. If they exist, create a SerialPort by constructing the SerialPort. freeAddress method, then close and dispose of them

@shingohu
Got the same issue in Windows. Can you please share your code?

[shingohu]

I have solved this problem. You can save the address of the last opened serial port. When hot restart occurs, check for any serial port addresses that have not been properly closed in the main function. If they exist, create a SerialPort by constructing the SerialPort. freeAddress method, then close and dispose of them

@shingohu Got the same issue in Windows. Can you please share your code?

 Future<void> hotRestart(int ptr) async {
    SerialPort port = SerialPort.fromAddress(ptr);
    if (port.isOpen) {
      port.close();
      port.dispose();
    }
  }