Error: Answer from Java side is empty

[wyattlansford]

Hello, I am running into a issue when trying to use the python openAI gym interface. Sorry I am posting this on the wrong repository, but there is no place to open an issue on the 4.5 version.

I am running on Gym-FightingICE 4.5. The issue happens when trying to initialize a game, before I can even take a single step in the environment

Traceback (most recent call last):
  File "/home/wlans4/anaconda3/envs/fighting_env/lib/python3.8/site-packages/py4j/java_gateway.py", line 1188, in send_command
    raise Py4JNetworkError("Answer from Java side is empty")
py4j.protocol.Py4JNetworkError: Answer from Java side is empty

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/wlans4/anaconda3/envs/fighting_env/lib/python3.8/site-packages/py4j/java_gateway.py", line 1014, in send_command
    response = connection.send_command(command)
  File "/home/wlans4/anaconda3/envs/fighting_env/lib/python3.8/site-packages/py4j/java_gateway.py", line 1192, in send_command
    raise Py4JNetworkError(
py4j.protocol.Py4JNetworkError: Error while receiving

The python code that I am running is here:

env_id = 1
envs = ['FightingiceDisplayNoFrameskip-v0',
            'FightingiceDisplayFrameskip-v0']
self.env = gym.make(envs[env_id], java_env_path="/home/wlans4/Documents/FightingAI/Gym-FightingICE/FTG4.50", port=4564, auto_start_up=True)
self.env.reset(p2="machete")

Here is my Java version:

java -version
java version "13.0.2" 2020-01-14
Java(TM) SE Runtime Environment (build 13.0.2+8)
Java HotSpot(TM) 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)

Here is my Python version:

python --version
Python 3.7.4

My linux distro:

lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.4 LTS

The game also opens in a window, but it is gets stuck forever while waiting for a response from the Java

If left running long enough (a few minutes), it also eventually says this:

raise Py4JNetworkError(msg, e)
py4j.protocol.Py4JNetworkError: An error occurred while trying to connect to the Java server (127.0.0.1:4564)

I have tried running

java -cp FightingICE.jar:./lib/lwjgl/:./lib/natives/linux/:./lib/* Main --py4j

as mentioned in another post, but it throws this error

 java -cp FightingICE.jar:./lib/lwjgl/:./lib/natives/linux/:./lib/* Main --py4j
Exception in thread "main" java.lang.NoClassDefFoundError: org/lwjgl/glfw/GLFWKeyCallbackI
	at Main.main(Main.java:19)
Caused by: java.lang.ClassNotFoundException: org.lwjgl.glfw.GLFWKeyCallbackI
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
	... 1 more

[stante]

Seems that you are using the Oracle version of Java. On the fighingice competition website the following is stated:

please install OpenJDK (8 or later; Oracle JDK 11 is not supported) from (updated on June 13, 2019)

I would try to use OpenJDK.