If leave and return to arduino exten. get Native Library already loaded error

[brandesNW]

This is a regression from 6.2.2 caused by the deprecation of the Object method finalize as of Java 9.
This was not caught by the compiler because the finalize method is obtained by reflection.

One way to reproduce:

1. Open Models Library Arduino Example
2. Click setup [Do not need to have an arduino board attached, just click OK in the dialog that says "No available arduino ports were found."]
3. Re-Open Arduino Example

Error message will appear

java.lang.UnsatisfiedLinkError: Native Library /Users/aab1638/.jssc/mac_os_x/libjSSC-2.6_x86_64.jnilib already loaded in another classloader
at java.base/jdk.internal.loader.NativeLibraries.loadLibrary(Unknown Source)
at java.base/jdk.internal.loader.NativeLibraries.loadLibrary(Unknown Source)
at java.base/java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.base/java.lang.Runtime.load0(Unknown Source)
at java.base/java.lang.System.load(Unknown Source)
at jssc.SerialNativeInterface.(SerialNativeInterface.java:172)
at jssc.SerialPortList.(SerialPortList.java:43)
at arduino.ArduinoExtension$Ports.report(ArduinoExtension.java:112)
at org.nlogo.prim._externreport.report(_externreport.java:31)
at org.nlogo.prim._asm_proceduresetup_setprocedurevariable_6.perform()
at org.nlogo.nvm.Context.stepConcurrent(Context.java:107)
at org.nlogo.nvm.ConcurrentJob.step(ConcurrentJob.scala:65)
at org.nlogo.job.JobThread.runPrimaryJobs(JobThread.scala:133)
at org.nlogo.job.JobThread.$anonfun$run$1(JobThread.scala:68)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
at scala.util.control.Exception$Catch.apply(Exception.scala:228)
at org.nlogo.api.Exceptions$.handling(Exceptions.scala:41)
at org.nlogo.job.JobThread.run(JobThread.scala:66)

NetLogo 6.3.0
main: org.nlogo.app.AppFrame
thread: AWT-EventQueue-0
OpenJDK 64-Bit Server VM 17.0.4 (BellSoft; 17.0.4+8-LTS)
operating system: Mac OS X 10.14.6 (x86_64 processor)
Scala version 2.12.16
JOGL: (3D View not initialized)
OpenGL Graphics: (3D View not initialized)
model: Arduino Example

02:15:18.265 TickStateChangeEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) JobThread
02:15:18.265 OutputEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:18.264 AddJobEvent (org.nlogo.window.ButtonWidget) AWT-EventQueue-0
02:15:18.192 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:18.144 InputBoxLoseFocusEvent (org.nlogo.window.ButtonWidget) AWT-EventQueue-0
02:15:17.986 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:17.782 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:17.580 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:17.379 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0
02:15:17.179 PeriodicUpdateEvent (org.nlogo.app.App$$anon$4 (org.nlogo.window.GUIWorkspace)) AWT-EventQueue-0

[brandesNW]

This is the problematic code

./extensions/arduino/src/main/java/ArduinoExtension.java

    //now unload the native library, so that if we're loading the extension
    //again on the same NetLogo run, it doesn't cause us troubles.
    try
    {
      ClassLoader classLoader = this.getClass().getClassLoader() ;
      java.lang.reflect.Field field = ClassLoader.class.getDeclaredField( "nativeLibraries" ) ;
      field.setAccessible(true);
      @SuppressWarnings("unchecked")
      Vector<Object> libs = (Vector<Object>) (field.get(classLoader)) ;
      for ( Object o : libs )
      {
        java.lang.reflect.Method finalize = o.getClass().getDeclaredMethod( "finalize" , new Class<?>[0] ) ;
        finalize.setAccessible( true ) ;
        finalize.invoke( o , new Object[0] ) ;
      }
    }
    catch( Exception e )
    {
      System.err.println( e.getMessage() ) ;
    }
  }

I have not been able to find on line a reliable way to unload a library
The documentation on how to replace finalize has not been helpful either.

Deprecate Finalization for Removal

Java 21 finalize

[brandesNW]

The workaround is for users who have already opened a model that uses the arduino extension to quit NetLogo if they need to again open a model that uses the arduino extension.