#37 Robot imported based on a jar file cannot run due to error: loader constraint violation

[darren]

Hi team,

I am trying to build a robot based on diamond and the code works when running using the .class file, but not work when I am trying to start a battle with a robot imported by the jar file built on the same source file.
Could you help take a look at this issue?

voidious.Diamond 1.0: Throwable: java.lang.LinkageError: loader constraint violation: when resolving method 'java.awt.geom.Point2D$Double voidious.utils.MovementPredictor.nextLocation(voidious.Diamond)' the class loader net.sf.robocode.host.security.RobotClassLoader @37d889de of the current class, voidious/radar/DiamondEyes, and the class loader 'app' for the method's defining class, voidious/utils/MovementPredictor, have different Class objects for the type voidious/Diamond used in the signature (voidious.radar.DiamondEyes is in unnamed module of loader net.sf.robocode.host.security.RobotClassLoader @37d889de, parent loader 'app'; voidious.utils.MovementPredictor is in unnamed module of loader 'app')

[darren]

Why there are two class loader for same class?
(RoboCode 1.9.5.1 and java 11)

[Flemming N. Larsen]

Why there are two class loader for same class?

Robocode is using its own class loader due to security reasons as it needs to put security restrictions on robots running within the same JVM.

Regarding the import error. Did you use the Robot/team packager of Robocode? f not, make sure to use it:

Call the packager from the menu:
Robot -> Package robot or team

If you did use the packager, I expect this to be a problem with never versions of Java making use of modules and putting more restrictions on Java Reflection. So you could try to run Robocode on an older version of Java e.g. version 8 or 11?

[darren]

Hi Flemming,
Yes I packed the jar file using "Robot/Package robot or team" menu.
OK, let me try with java 8, thanks!

[darren]

Hi @fnl, help!
The problem still there, jdk 8, could you help take a look?
voidious.Diamond 1.0: Throwable: java.lang.LinkageError: loader constraint violation: when resolving method "voidious.utils.MovementPredictor.nextLocation(Lvoidious/Diamond;)Ljava/awt/geom/Point2D$Double;" the class loader (instance of net/sf/robocode/host/security/RobotClassLoader) of the current class, voidious/radar/DiamondEyes, and the class loader (instance of sun/misc/Launcher$AppClassLoader) for the method's defining class, voidious/utils/MovementPredictor, have different Class objects for the type voidious/Diamond used in the signature

[Flemming N. Larsen]

OK. I will have a look and see if I can reproduce it. And if so, I will figure out how it can be solved. 👍

[Flemming N. Larsen]

I can reproduce the problem, and trying to find a prober fix for it.

[darren]

@fnl Thanks you, looking forward your answer.

[Flemming N. Larsen]

For now, a temporary fix is to set the -DNOSECURITY=true option on the command line. That is, put this line in the java command in the robocode.bat or robocode.sh file.
This disables the security manager and changes the way the classes are loaded.

I still work on a real fix. But it is not an easy one, and could take some time.

[Flemming N. Larsen]

@darren
I have made a fix in the RobotClassLoader that works on my system, and I should like you to try it out with an alpha version of the next version 1.9.5.2:
https://robocode.sourceforge.io/files/robocode-1.9.5.2-alfa-setup.jar

If it works, I will make a release soon.

[darren]

@fnl Thank you for your quick response.
I tried with the new alfa version and it works for me, when can we get the release version of 1.9.5.2?

[Flemming N. Larsen]

I have created a new release 1.9.5.2 just now. You can download it from here:
https://sourceforge.net/projects/robocode/files/robocode/1.9.5.2/robocode-1.9.5.2-setup.jar