[Bug Fix] Fix crash if spawn is delayed in multi-env

com.unity.ml-agents/CHANGELOG.md

@@ -32,6 +32,7 @@ removed when training with a player. The Editor still requires it to be clamped
 - Fix a compile warning about using an obsolete enum in `GrpcExtensions.cs`. (#4812)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 - Fixed a bug that would cause an exception when `RunOptions` was deserialized via `pickle`. (#4842)
+- Fixed a bug that can cause a crash if a behavior can appear during training in multi-environment training. (#4872)
 - Fixed the computation of entropy for continuous actions. (#4869)
 
 

ml-agents/mlagents/trainers/subprocess_env_manager.py

@@ -310,8 +310,11 @@ def set_env_parameters(self, config: Dict = None) -> None:
 
     @property
     def training_behaviors(self) -> Dict[BehaviorName, BehaviorSpec]:
-        self.env_workers[0].send(EnvironmentCommand.BEHAVIOR_SPECS)
-        return self.env_workers[0].recv().payload
+        result: Dict[BehaviorName, BehaviorSpec] = {}
+        for worker in self.env_workers:
+            worker.send(EnvironmentCommand.BEHAVIOR_SPECS)
+            result.update(worker.recv().payload)
+        return result
 
     def close(self) -> None:
         logger.debug("SubprocessEnvManager closing.")

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

@@ -102,6 +102,33 @@ def test_reset_collects_results_from_all_envs(self, mock_create_worker):
             )
         assert res == list(map(lambda ew: ew.previous_step, manager.env_workers))
 
+    @mock.patch(
+        "mlagents.trainers.subprocess_env_manager.SubprocessEnvManager.create_worker"
+    )
+    def test_training_behaviors_collects_results_from_all_envs(
+        self, mock_create_worker
+    ):
+        def create_worker_mock(worker_id, step_queue, env_factor, engine_c):
+            return MockEnvWorker(
+                worker_id,
+                EnvironmentResponse(
+                    EnvironmentCommand.RESET, worker_id, {f"key{worker_id}": worker_id}
+                ),
+            )
+
+        mock_create_worker.side_effect = create_worker_mock
+        manager = SubprocessEnvManager(
+            mock_env_factory, EngineConfig.default_config(), 4
+        )
+
+        res = manager.training_behaviors
+        for env in manager.env_workers:
+            env.send.assert_called_with(EnvironmentCommand.BEHAVIOR_SPECS)
+            env.recv.assert_called()
+        for worker_id in range(4):
+            assert f"key{worker_id}" in res
+            assert res[f"key{worker_id}"] == worker_id
+
     @mock.patch(
         "mlagents.trainers.subprocess_env_manager.SubprocessEnvManager.create_worker"
     )