[Bug fix] Hard reset when team changes (#3870)

Project/Assets/ML-Agents/Examples/Tennis/Prefabs/TennisArea.prefab

   m_Name: 
   m_EditorClassIdentifier: 
   m_BrainParameters:
-    vectorObservationSize: 9
-    numStackedVectorObservations: 3
-    vectorActionSize: 03000000
-    vectorActionDescriptions: []
-    vectorActionSpaceType: 1
+    VectorObservationSize: 9
+    NumStackedVectorObservations: 3
+    VectorActionSize: 03000000
+    VectorActionDescriptions: []
+    VectorActionSpaceType: 1
   m_Model: {fileID: 11400000, guid: d6c5e749e4ceb4cf79640a5955706d3d, type: 3}
   m_InferenceDevice: 0
   m_BehaviorType: 0
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  maxStep: 0
+  MaxStep: 0
   ball: {fileID: 1273406647218856}
   invertX: 0
   score: 0
   m_EditorClassIdentifier: 
   DecisionPeriod: 5
   TakeActionsBetweenDecisions: 1
-  offsetStep: 0
 --- !u!114 &6467897465973556822
 MonoBehaviour:
   m_ObjectHideFlags: 0
   m_Name: 
   m_EditorClassIdentifier: 
   m_BrainParameters:
-    vectorObservationSize: 9
-    numStackedVectorObservations: 3
-    vectorActionSize: 03000000
-    vectorActionDescriptions: []
-    vectorActionSpaceType: 1
+    VectorObservationSize: 9
+    NumStackedVectorObservations: 3
+    VectorActionSize: 03000000
+    VectorActionDescriptions: []
+    VectorActionSpaceType: 1
   m_Model: {fileID: 11400000, guid: d6c5e749e4ceb4cf79640a5955706d3d, type: 3}
   m_InferenceDevice: 0
   m_BehaviorType: 0
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  maxStep: 0
+  MaxStep: 0
   ball: {fileID: 1273406647218856}
   invertX: 1
   score: 0
   m_EditorClassIdentifier: 
   DecisionPeriod: 5
   TakeActionsBetweenDecisions: 1
-  offsetStep: 0
 --- !u!114 &1420140102966759323
 MonoBehaviour:
   m_ObjectHideFlags: 0

ml-agents/mlagents/trainers/ghost/controller.py

         self._learning_team: int = -1
         # Dict from team id to GhostTrainer for ELO calculation
         self._ghost_trainers: Dict[int, GhostTrainer] = {}
+        # Signals to the trainer control to perform a hard change_training_team
+        self._changed_training_team = False
 
     @property
     def get_learning_team(self) -> int:
         """
         return self._learning_team
+
+    def should_reset(self) -> bool:
+        """
+        Whether or not team change occurred. Causes full reset in trainer_controller
+        :return: The truth value of the team changing
+        """
+        changed_team = self._changed_training_team
+        if self._changed_training_team:
+            self._changed_training_team = False
+        return changed_team
 
     def subscribe_team_id(self, team_id: int, trainer: GhostTrainer) -> None:
         """
         logger.debug(
             "Learning team {} swapped on step {}".format(self._learning_team, step)
         )
+        self._changed_training_team = True
 
     # Adapted from https://github.com/Unity-Technologies/ml-agents/pull/1975 and
     # https://metinmediamath.wordpress.com/2013/11/27/how-to-calculate-the-elo-rating-including-example/

ml-agents/mlagents/trainers/tests/simple_test_envs.py

         self.goal[name] = self.random.choice([-1, 1])
         self.positions[name] = [0.0 for _ in range(self.action_size)]
         self.step_count[name] = 0
-        self.final_rewards[name].append(self.rewards[name])
         self.rewards[name] = 0
         self.agent_id[name] = self.agent_id[name] + 1
 
         decision_step = DecisionSteps(m_vector_obs, m_reward, m_agent_id, action_mask)
         terminal_step = TerminalSteps.empty(self.behavior_spec)
         if done:
+            self.final_rewards[name].append(self.rewards[name])
             self._reset_agent(name)
             new_vector_obs = self._make_obs(self.goal[name])
             (
         decision_step = DecisionSteps(m_vector_obs, m_reward, m_agent_id, action_mask)
         terminal_step = TerminalSteps.empty(self.behavior_spec)
         if done:
+            self.final_rewards[name].append(self.rewards[name])
             self._reset_agent(name)
             recurrent_obs_val = (
                 self.goal[name] if self.step_count[name] <= self.num_show_steps else 0

ml-agents/mlagents/trainers/tests/test_trainer_controller.py

 
 from mlagents.tf_utils import tf
 from mlagents.trainers.trainer_controller import TrainerController
+from mlagents.trainers.ghost.controller import GhostController
+    trainer_factory_mock = MagicMock()
+    trainer_factory_mock.ghost_controller = GhostController()
-        trainer_factory=None,
+        trainer_factory=trainer_factory_mock,
         model_path="test_model_path",
         summaries_dir="test_summaries_dir",
         run_id="test_run_id",
 @patch.object(tf, "set_random_seed")
 def test_initialization_seed(numpy_random_seed, tensorflow_set_seed):
     seed = 27
+    trainer_factory_mock = MagicMock()
+    trainer_factory_mock.ghost_controller = GhostController()
-        trainer_factory=None,
+        trainer_factory=trainer_factory_mock,
         model_path="",
         summaries_dir="",
         run_id="1",

ml-agents/mlagents/trainers/trainer_controller.py

         self.meta_curriculum = meta_curriculum
         self.sampler_manager = sampler_manager
         self.resampling_interval = resampling_interval
+        self.ghost_controller = self.trainer_factory.ghost_controller
 
         self.trainer_threads: List[threading.Thread] = []
         self.kill_trainers = False
             and (self.resampling_interval)
             and (steps % self.resampling_interval == 0)
         )
-        if meta_curriculum_reset or generalization_reset:
+        ghost_controller_reset = self.ghost_controller.should_reset()
+        if meta_curriculum_reset or generalization_reset or ghost_controller_reset:
             self.end_trainer_episodes(env, lessons_incremented)
 
     @timed