Unable to run code concurrently.

[nikitinalexx]

Hi, I'm trying to run some different games concurrently.

for (int t = 0; t < 50; t++) {
            Thread thread = new Thread(() -> {
                  MultiplayerGameRunner gameRunner = new MultiplayerGameRunner();
                  gameRunner.addAgent(Player.class);
                  gameRunner.addAgent(Player.class);
                  gameRunner.simulate();
            }
}

It gives this stacktrace.
Exception in thread "Thread-396" java.util.ConcurrentModificationException
at java.base/java.util.HashMap.forEach(HashMap.java:1339)
at com.codingame.gameengine.module.entities.WorldState.diffFromOtherWorldState(WorldState.java:83)
at com.codingame.gameengine.module.entities.GraphicEntityModule.sendFrameData(GraphicEntityModule.java:187)
at com.codingame.gameengine.module.entities.GraphicEntityModule.onGameInit(GraphicEntityModule.java:326)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
at com.codingame.gameengine.core.GameManager.start(GameManager.java:99)
at com.codingame.gameengine.core.RefereeMain.start(RefereeMain.java:49)
at com.codingame.gameengine.runner.RefereeAgent$1.run(RefereeAgent.java:58)

[nikitinalexx]

Created a ticket in game engine project.
CodinGame/codingame-game-engine#15