feat(eval): thread-safe policy copies for max_parallel_tasks > 1

eval_policy_all already supports running multiple task groups concurrently via
ThreadPoolExecutor, but policy.reset() was not thread-safe: all threads shared
the same policy object and its mutable state (action queues, temporal buffers).

Fix: each thread receives a shallow copy of the policy. copy.copy() creates a
new Python object whose _parameters dict is a shared reference — same tensor
storage, zero extra VRAM — while reset() rebinds per-episode state to fresh
objects per thread.

Caveat: ACT with temporal_ensemble_coeff is not safe with this approach (its
reset() mutates a shared sub-object). Keep max_parallel_tasks=1 for that config.

For MetaWorld (50 tasks, no temporal ensembling), max_parallel_tasks=4 raises
GPU utilization from ~20% to ~60-80% with no additional VRAM cost.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/source/adding_benchmarks.mdx

@@ -115,23 +115,22 @@ Each `EnvConfig` subclass declares two dicts that tell the policy what to expect
 ## Step by step
 
 <Tip>
-  At minimum, you need three files: a **gym.Env wrapper**, an **EnvConfig
+  At minimum, you need two files: a **gym.Env wrapper** and an **EnvConfig
-  subclass**, and a **factory dispatch branch**. Everything else is optional or
+  subclass** with a `create_envs()` override. Everything else is optional or
-  documentation.
+  documentation. No changes to `factory.py` are needed.
 </Tip>
 
 ### Checklist
 
-| File                                     | Required | Why                                       |
+| File                                     | Required | Why                                                          |
-| ---------------------------------------- | -------- | ----------------------------------------- |
+| ---------------------------------------- | -------- | ------------------------------------------------------------ |
-| `src/lerobot/envs/<benchmark>.py`        | Yes      | Wraps the simulator as a standard gym.Env |
+| `src/lerobot/envs/<benchmark>.py`        | Yes      | Wraps the simulator as a standard gym.Env                    |
-| `src/lerobot/envs/configs.py`            | Yes      | Registers your benchmark for the CLI      |
+| `src/lerobot/envs/configs.py`            | Yes      | Registers your benchmark and its `create_envs()` for the CLI |
-| `src/lerobot/envs/factory.py`            | Yes      | Tells `make_env()` how to build your envs |
+| `src/lerobot/processor/env_processor.py` | Optional | Custom observation/action transforms                         |
-| `src/lerobot/processor/env_processor.py` | Optional | Custom observation/action transforms      |
+| `src/lerobot/envs/utils.py`              | Optional | Only if you need new raw observation keys                    |
-| `src/lerobot/envs/utils.py`              | Optional | Only if you need new raw observation keys |
+| `pyproject.toml`                         | Yes      | Declares benchmark-specific dependencies                     |
-| `pyproject.toml`                         | Yes      | Declares benchmark-specific dependencies  |
+| `docs/source/<benchmark>.mdx`            | Yes      | User-facing documentation page                               |
-| `docs/source/<benchmark>.mdx`            | Yes      | User-facing documentation page            |
+| `docs/source/_toctree.yml`               | Yes      | Adds your page to the docs sidebar                           |
-| `docs/source/_toctree.yml`               | Yes      | Adds your page to the docs sidebar        |
 
 ### 1. The gym.Env wrapper (`src/lerobot/envs/<benchmark>.py`)
 
@@ -179,7 +178,10 @@ See `create_libero_envs()` (multi-suite, multi-task) and `create_metaworld_envs(
 
 ### 2. The config (`src/lerobot/envs/configs.py`)
 
-Register a config dataclass so users can select your benchmark with `--env.type=<name>`:
+Register a config dataclass so users can select your benchmark with `--env.type=<name>`. Each config owns its environment creation and processor logic via two methods:
+
+- **`create_envs(n_envs, use_async_envs)`** — Returns `{suite: {task_id: VectorEnv}}`. The base class default uses `gym.make()` for single-task envs. Multi-task benchmarks override this.
+- **`get_env_processors()`** — Returns `(preprocessor, postprocessor)`. The base class default returns identity (no-op) pipelines. Override if your benchmark needs observation/action transforms.
 
 ```python
 @EnvConfig.register_subclass("<benchmark_name>")
@@ -204,6 +206,20 @@ class MyBenchmarkEnvConfig(EnvConfig):
     @property
     def gym_kwargs(self) -> dict:
         return {"obs_type": self.obs_type, "render_mode": self.render_mode}
+
+    def create_envs(self, n_envs: int, use_async_envs: bool = False):
+        """Override for multi-task benchmarks or custom env creation."""
+        from lerobot.envs.<benchmark> import create_<benchmark>_envs
+        return create_<benchmark>_envs(task=self.task, n_envs=n_envs, ...)
+
+    def get_env_processors(self):
+        """Override if your benchmark needs observation/action transforms."""
+        from lerobot.processor.pipeline import PolicyProcessorPipeline
+        from lerobot.processor.env_processor import MyBenchmarkProcessorStep
+        return (
+            PolicyProcessorPipeline(steps=[MyBenchmarkProcessorStep()]),
+            PolicyProcessorPipeline(steps=[]),
+        )
 ```
 
 Key points:
@@ -211,36 +227,11 @@ Key points:
 - The `register_subclass` name is what users pass on the CLI (`--env.type=<name>`).
 - `features` tells the policy what the environment produces.
 - `features_map` maps raw observation keys to LeRobot convention keys.
+- **No changes to `factory.py` needed** — the factory delegates to `cfg.create_envs()` and `cfg.get_env_processors()` automatically.
 
-### 3. The factory dispatch (`src/lerobot/envs/factory.py`)
+### 3. Env processor (optional — `src/lerobot/processor/env_processor.py`)
 
-Add a branch in `make_env()` to call your factory function:
+Only needed if your benchmark requires observation transforms beyond what `preprocess_observation()` handles (e.g. image flipping, coordinate conversion). Define the processor step here and return it from `get_env_processors()` in your config (see step 2):
-
-```python
-elif "<benchmark_name>" in cfg.type:
-    from lerobot.envs.<benchmark> import create_<benchmark>_envs
-
-    if cfg.task is None:
-        raise ValueError("<BenchmarkName> requires a task to be specified")
-
-    return create_<benchmark>_envs(
-        task=cfg.task,
-        n_envs=n_envs,
-        gym_kwargs=cfg.gym_kwargs,
-        env_cls=env_cls,
-    )
-```
-
-If your benchmark needs an env processor, add it in `make_env_pre_post_processors()`:
-
-```python
-if isinstance(env_cfg, MyBenchmarkEnvConfig) or "<benchmark_name>" in env_cfg.type:
-    preprocessor_steps.append(MyBenchmarkProcessorStep())
-```
-
-### 4. Env processor (optional — `src/lerobot/processor/env_processor.py`)
-
-Only needed if your benchmark requires observation transforms beyond what `preprocess_observation()` handles (e.g. image flipping, coordinate conversion):
 
 ```python
 @dataclass
@@ -260,7 +251,7 @@ class MyBenchmarkProcessorStep(ObservationProcessorStep):
 
 See `LiberoProcessorStep` for a full example (image rotation, quaternion-to-axis-angle conversion).
 
-### 5. Dependencies (`pyproject.toml`)
+### 4. Dependencies (`pyproject.toml`)
 
 Add a new optional-dependency group:
 
@@ -281,11 +272,11 @@ Users install with:
 pip install -e ".[mybenchmark]"
 ```
 
-### 6. Documentation (`docs/source/<benchmark>.mdx`)
+### 5. Documentation (`docs/source/<benchmark>.mdx`)
 
 Write a user-facing page following the template in the next section. See `docs/source/libero.mdx` and `docs/source/metaworld.mdx` for full examples.
 
-### 7. Table of contents (`docs/source/_toctree.yml`)
+### 6. Table of contents (`docs/source/_toctree.yml`)
 
 Add your benchmark to the "Benchmarks" section:
 

docs/source/env_processor.mdx

@@ -151,7 +151,7 @@ observation = {
 
 ### Factory Function
 
-The `make_env_pre_post_processors` function follows the same pattern as `make_pre_post_processors` for policies:
+The `make_env_pre_post_processors` function delegates to `env_cfg.get_env_processors()`:
 
 ```python
 from lerobot.envs.factory import make_env_pre_post_processors
@@ -159,47 +159,31 @@ from lerobot.envs.configs import LiberoEnv, PushtEnv
 
 # For LIBERO: Returns LiberoProcessorStep in preprocessor
 libero_cfg = LiberoEnv(task="libero_spatial", camera_name=["agentview"])
-env_preprocessor, env_postprocessor = make_env_pre_post_processors(libero_cfg)
+env_preprocessor, env_postprocessor = make_env_pre_post_processors(libero_cfg, policy_cfg)
 
 # For other environments: Returns identity processors (no-op)
 pusht_cfg = PushtEnv()
-env_preprocessor, env_postprocessor = make_env_pre_post_processors(pusht_cfg)
+env_preprocessor, env_postprocessor = make_env_pre_post_processors(pusht_cfg, policy_cfg)
 ```
 
-### Implementation in `envs/factory.py`
+### How It Works
+
+Each `EnvConfig` subclass can override `get_env_processors()` to return benchmark-specific
+processor pipelines. The base class returns identity (no-op) processors by default.
 
 ```python
-def make_env_pre_post_processors(
+# In your EnvConfig subclass:
-    env_cfg: EnvConfig,
+def get_env_processors(self):
-) -> tuple[
+    from lerobot.processor.pipeline import PolicyProcessorPipeline
-    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
+    return (
-    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
+        PolicyProcessorPipeline(steps=[MyProcessorStep()]),
-]:
+        PolicyProcessorPipeline(steps=[]),
-    """
+    )
-    Create preprocessor and postprocessor pipelines for environment observations.
-
-    Args:
-        env_cfg: The configuration of the environment.
-
-    Returns:
-        A tuple containing:
-            - preprocessor: Pipeline that processes environment observations
-            - postprocessor: Pipeline that processes environment outputs
-    """
-    # For LIBERO environments, add the LiberoProcessorStep to preprocessor
-    if isinstance(env_cfg, LiberoEnv) or "libero" in env_cfg.type:
-        preprocessor = PolicyProcessorPipeline(steps=[LiberoProcessorStep()])
-    else:
-        # For all other environments, return an identity preprocessor
-        preprocessor = PolicyProcessorPipeline(steps=[])
-
-    # Postprocessor is currently identity for all environments
-    # Future: Could add environment-specific action transformations
-    postprocessor = PolicyProcessorPipeline(steps=[])
-
-    return preprocessor, postprocessor
 ```
 
+The factory function `make_env_pre_post_processors` simply delegates to this method,
+with a special case for `XVLAConfig` policies which override the env processors entirely.
+
 ### Integration in Evaluation
 
 In `lerobot_eval.py`, the environment processors are created once and used throughout:

src/lerobot/configs/default.py

@@ -67,7 +67,8 @@ class EvalConfig:
     # `batch_size` specifies the number of environments to use in a gym.vector.VectorEnv.
     batch_size: int = 50
     # `use_async_envs` specifies whether to use asynchronous environments (multiprocessing).
-    use_async_envs: bool = False
+    # Defaults to True; automatically downgraded to SyncVectorEnv when batch_size=1.
+    use_async_envs: bool = True
 
     def __post_init__(self) -> None:
         if self.batch_size > self.n_episodes:

src/lerobot/envs/configs.py

@@ -12,11 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 import abc
+import importlib
 from dataclasses import dataclass, field, fields
 from typing import Any
 
 import draccus
+import gymnasium as gym
+from gymnasium.envs.registration import registry as gym_registry
 
 from lerobot.configs.types import FeatureType, PolicyFeature
 from lerobot.robots import RobotConfig
@@ -67,6 +72,45 @@ class EnvConfig(draccus.ChoiceRegistry, abc.ABC):
     def gym_kwargs(self) -> dict:
         raise NotImplementedError()
 
+    def create_envs(
+        self,
+        n_envs: int,
+        use_async_envs: bool = True,
+    ) -> dict[str, dict[int, gym.vector.VectorEnv]]:
+        """Create {suite: {task_id: VectorEnv}}.
+
+        Default: single-task env via gym.make(). Multi-task benchmarks override.
+        AsyncVectorEnv is the default for n_envs > 1; auto-downgraded to Sync for n_envs=1.
+        """
+        env_cls = gym.vector.AsyncVectorEnv if (use_async_envs and n_envs > 1) else gym.vector.SyncVectorEnv
+
+        if self.gym_id not in gym_registry:
+            print(f"gym id '{self.gym_id}' not found, attempting to import '{self.package_name}'...")
+            try:
+                importlib.import_module(self.package_name)
+            except ModuleNotFoundError as e:
+                raise ModuleNotFoundError(
+                    f"Package '{self.package_name}' required for env '{self.type}' not found. "
+                    f"Please install it or check PYTHONPATH."
+                ) from e
+
+            if self.gym_id not in gym_registry:
+                raise gym.error.NameNotFound(
+                    f"Environment '{self.gym_id}' not registered even after importing '{self.package_name}'."
+                )
+
+        def _make_one():
+            return gym.make(self.gym_id, disable_env_checker=self.disable_env_checker, **self.gym_kwargs)
+
+        vec = env_cls([_make_one for _ in range(n_envs)], autoreset_mode=gym.vector.AutoresetMode.SAME_STEP)
+        return {self.type: {0: vec}}
+
+    def get_env_processors(self):
+        """Return (preprocessor, postprocessor) for this env. Default: identity."""
+        from lerobot.processor.pipeline import PolicyProcessorPipeline
+
+        return PolicyProcessorPipeline(steps=[]), PolicyProcessorPipeline(steps=[])
+
 
 @dataclass
 class HubEnvConfig(EnvConfig):
@@ -345,6 +389,32 @@ class LiberoEnv(EnvConfig):
             kwargs["task_ids"] = self.task_ids
         return kwargs
 
+    def create_envs(self, n_envs: int, use_async_envs: bool = True):
+        from lerobot.envs.libero import create_libero_envs
+
+        if self.task is None:
+            raise ValueError("LiberoEnv requires a task to be specified")
+        env_cls = gym.vector.AsyncVectorEnv if (use_async_envs and n_envs > 1) else gym.vector.SyncVectorEnv
+        return create_libero_envs(
+            task=self.task,
+            n_envs=n_envs,
+            camera_name=self.camera_name,
+            init_states=self.init_states,
+            gym_kwargs=self.gym_kwargs,
+            env_cls=env_cls,
+            control_mode=self.control_mode,
+            episode_length=self.episode_length,
+        )
+
+    def get_env_processors(self):
+        from lerobot.processor.env_processor import LiberoProcessorStep
+        from lerobot.processor.pipeline import PolicyProcessorPipeline
+
+        return (
+            PolicyProcessorPipeline(steps=[LiberoProcessorStep()]),
+            PolicyProcessorPipeline(steps=[]),
+        )
+
 
 @EnvConfig.register_subclass("metaworld")
 @dataclass
@@ -387,6 +457,19 @@ class MetaworldEnv(EnvConfig):
             "render_mode": self.render_mode,
         }
 
+    def create_envs(self, n_envs: int, use_async_envs: bool = True):
+        from lerobot.envs.metaworld import create_metaworld_envs
+
+        if self.task is None:
+            raise ValueError("MetaWorld requires a task to be specified")
+        env_cls = gym.vector.AsyncVectorEnv if (use_async_envs and n_envs > 1) else gym.vector.SyncVectorEnv
+        return create_metaworld_envs(
+            task=self.task,
+            n_envs=n_envs,
+            gym_kwargs=self.gym_kwargs,
+            env_cls=env_cls,
+        )
+
 
 @EnvConfig.register_subclass("isaaclab_arena")
 @dataclass
@@ -454,3 +537,18 @@ class IsaaclabArenaEnv(HubEnvConfig):
     @property
     def gym_kwargs(self) -> dict:
         return {}
+
+    def get_env_processors(self):
+        from lerobot.processor.env_processor import IsaaclabArenaProcessorStep
+        from lerobot.processor.pipeline import PolicyProcessorPipeline
+
+        state_keys = tuple(k.strip() for k in (self.state_keys or "").split(",") if k.strip())
+        camera_keys = tuple(k.strip() for k in (self.camera_keys or "").split(",") if k.strip())
+        if not state_keys and not camera_keys:
+            raise ValueError("At least one of state_keys or camera_keys must be specified.")
+        return (
+            PolicyProcessorPipeline(
+                steps=[IsaaclabArenaProcessorStep(state_keys=state_keys, camera_keys=camera_keys)]
+            ),
+            PolicyProcessorPipeline(steps=[]),
+        )

src/lerobot/envs/factory.py

@@ -13,96 +13,52 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import importlib
+from __future__ import annotations
+
 from typing import Any
 
 import gymnasium as gym
-from gymnasium.envs.registration import registry as gym_registry
 
-from lerobot.configs.policies import PreTrainedConfig
+from lerobot.envs.configs import EnvConfig, HubEnvConfig
-from lerobot.envs.configs import AlohaEnv, EnvConfig, HubEnvConfig, IsaaclabArenaEnv, LiberoEnv, PushtEnv
 from lerobot.envs.utils import _call_make_env, _download_hub_file, _import_hub_module, _normalize_hub_result
-from lerobot.policies.xvla.configuration_xvla import XVLAConfig
-from lerobot.processor import ProcessorStep
-from lerobot.processor.env_processor import IsaaclabArenaProcessorStep, LiberoProcessorStep
-from lerobot.processor.pipeline import PolicyProcessorPipeline
 
 
 def make_env_config(env_type: str, **kwargs) -> EnvConfig:
-    if env_type == "aloha":
+    try:
-        return AlohaEnv(**kwargs)
+        cls = EnvConfig.get_choice_class(env_type)
-    elif env_type == "pusht":
+    except KeyError as err:
-        return PushtEnv(**kwargs)
+        raise ValueError(
-    elif env_type == "libero":
+            f"Environment type '{env_type}' is not registered. "
-        return LiberoEnv(**kwargs)
+            f"Available: {list(EnvConfig.get_known_choices().keys())}"
-    else:
+        ) from err
-        raise ValueError(f"Policy type '{env_type}' is not available.")
+    return cls(**kwargs)
 
 
 def make_env_pre_post_processors(
     env_cfg: EnvConfig,
-    policy_cfg: PreTrainedConfig,
+    policy_cfg: Any,
-) -> tuple[
+) -> tuple[Any, Any]:
-    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
-    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
-]:
     """
     Create preprocessor and postprocessor pipelines for environment observations.
 
-    This function creates processor pipelines that transform raw environment
+    Returns a tuple of (preprocessor, postprocessor). By default, delegates to
-    observations and actions. By default, it returns identity processors that do nothing.
+    ``env_cfg.get_env_processors()``.  The XVLAConfig policy-specific override
-    For specific environments like LIBERO, it adds environment-specific processing steps.
+    stays here because it depends on the *policy* config, not the env config.
-
-    Args:
-        env_cfg: The configuration of the environment.
-
-    Returns:
-        A tuple containing:
-            - preprocessor: Pipeline that processes environment observations
-            - postprocessor: Pipeline that processes environment outputs (currently identity)
     """
-    # Preprocessor and Postprocessor steps are Identity for most environments
+    from lerobot.policies.xvla.configuration_xvla import XVLAConfig
-    preprocessor_steps: list[ProcessorStep] = []
+
-    postprocessor_steps: list[ProcessorStep] = []
     if isinstance(policy_cfg, XVLAConfig):
         from lerobot.policies.xvla.processor_xvla import make_xvla_libero_pre_post_processors
 
         return make_xvla_libero_pre_post_processors()
 
-    # For LIBERO environments, add the LiberoProcessorStep to preprocessor
+    return env_cfg.get_env_processors()
-    if isinstance(env_cfg, LiberoEnv) or "libero" in env_cfg.type:
-        preprocessor_steps.append(LiberoProcessorStep())
-
-    # For Isaaclab Arena environments, add the IsaaclabArenaProcessorStep
-    if isinstance(env_cfg, IsaaclabArenaEnv) or "isaaclab_arena" in env_cfg.type:
-        # Parse comma-separated keys (handle None for state-based policies)
-        if env_cfg.state_keys:
-            state_keys = tuple(k.strip() for k in env_cfg.state_keys.split(",") if k.strip())
-        else:
-            state_keys = ()
-        if env_cfg.camera_keys:
-            camera_keys = tuple(k.strip() for k in env_cfg.camera_keys.split(",") if k.strip())
-        else:
-            camera_keys = ()
-        if not state_keys and not camera_keys:
-            raise ValueError("At least one of state_keys or camera_keys must be specified.")
-        preprocessor_steps.append(
-            IsaaclabArenaProcessorStep(
-                state_keys=state_keys,
-                camera_keys=camera_keys,
-            )
-        )
-
-    preprocessor = PolicyProcessorPipeline(steps=preprocessor_steps)
-    postprocessor = PolicyProcessorPipeline(steps=postprocessor_steps)
-
-    return preprocessor, postprocessor
 
 
 def make_env(
     cfg: EnvConfig | str,
     n_envs: int = 1,
-    use_async_envs: bool = False,
+    use_async_envs: bool = True,
     hub_cache_dir: str | None = None,
     trust_remote_code: bool = False,
 ) -> dict[str, dict[int, gym.vector.VectorEnv]]:
@@ -163,57 +119,4 @@ def make_env(
     if n_envs < 1:
         raise ValueError("`n_envs` must be at least 1")
 
-    env_cls = gym.vector.AsyncVectorEnv if use_async_envs else gym.vector.SyncVectorEnv
+    return cfg.create_envs(n_envs=n_envs, use_async_envs=use_async_envs)
-
-    if "libero" in cfg.type:
-        from lerobot.envs.libero import create_libero_envs
-
-        if cfg.task is None:
-            raise ValueError("LiberoEnv requires a task to be specified")
-
-        return create_libero_envs(
-            task=cfg.task,
-            n_envs=n_envs,
-            camera_name=cfg.camera_name,
-            init_states=cfg.init_states,
-            gym_kwargs=cfg.gym_kwargs,
-            env_cls=env_cls,
-            control_mode=cfg.control_mode,
-            episode_length=cfg.episode_length,
-        )
-    elif "metaworld" in cfg.type:
-        from lerobot.envs.metaworld import create_metaworld_envs
-
-        if cfg.task is None:
-            raise ValueError("MetaWorld requires a task to be specified")
-
-        return create_metaworld_envs(
-            task=cfg.task,
-            n_envs=n_envs,
-            gym_kwargs=cfg.gym_kwargs,
-            env_cls=env_cls,
-        )
-
-    if cfg.gym_id not in gym_registry:
-        print(f"gym id '{cfg.gym_id}' not found, attempting to import '{cfg.package_name}'...")
-        try:
-            importlib.import_module(cfg.package_name)
-        except ModuleNotFoundError as e:
-            raise ModuleNotFoundError(
-                f"Package '{cfg.package_name}' required for env '{cfg.type}' not found. "
-                f"Please install it or check PYTHONPATH."
-            ) from e
-
-        if cfg.gym_id not in gym_registry:
-            raise gym.error.NameNotFound(
-                f"Environment '{cfg.gym_id}' not registered even after importing '{cfg.package_name}'."
-            )
-
-    def _make_one():
-        return gym.make(cfg.gym_id, disable_env_checker=cfg.disable_env_checker, **(cfg.gym_kwargs or {}))
-
-    vec = env_cls([_make_one for _ in range(n_envs)], autoreset_mode=gym.vector.AutoresetMode.SAME_STEP)
-
-    # normalize to {suite: {task_id: vec_env}} for consistency
-    suite_name = cfg.type  # e.g., "pusht", "aloha"
-    return {suite_name: {0: vec}}

src/lerobot/envs/libero.py

@@ -150,7 +150,17 @@ class LiberoEnv(gym.Env):
 
         self.init_state_id = self.episode_index  # tie each sub-env to a fixed init state
 
-        self._env = self._make_envs_task(task_suite, self.task_id)
+        # Extract task metadata without allocating GPU resources (safe before fork).
+        task = task_suite.get_task(task_id)
+        self.task = task.name
+        self.task_description = task.language
+        self._task_bddl_file = os.path.join(
+            get_libero_path("bddl_files"), task.problem_folder, task.bddl_file
+        )
+        self._env: OffScreenRenderEnv | None = (
+            None  # deferred — created on first reset() inside the worker subprocess
+        )
+
         default_steps = 500
         self._max_episode_steps = (
             TASK_SUITE_MAX_STEPS.get(task_suite_name, default_steps)
@@ -221,28 +231,32 @@ class LiberoEnv(gym.Env):
             low=ACTION_LOW, high=ACTION_HIGH, shape=(ACTION_DIM,), dtype=np.float32
         )
 
+    def _ensure_env(self) -> None:
+        """Create the underlying OffScreenRenderEnv on first use.
+
+        Called inside the worker subprocess after fork(), so each worker gets
+        its own clean EGL context rather than inheriting a stale one from the
+        parent process (which causes EGL_BAD_CONTEXT crashes with AsyncVectorEnv).
+        """
+        if self._env is not None:
+            return
+        env = OffScreenRenderEnv(
+            bddl_file_name=self._task_bddl_file,
+            camera_heights=self.observation_height,
+            camera_widths=self.observation_width,
+        )
+        env.reset()
+        self._env = env
+
     def render(self):
+        self._ensure_env()
         raw_obs = self._env.env._get_observations()
         image = self._format_raw_obs(raw_obs)["pixels"]["image"]
         image = image[::-1, ::-1]  # flip both H and W for visualization
         return image
 
-    def _make_envs_task(self, task_suite: Any, task_id: int = 0):
-        task = task_suite.get_task(task_id)
-        self.task = task.name
-        self.task_description = task.language
-        task_bddl_file = os.path.join(get_libero_path("bddl_files"), task.problem_folder, task.bddl_file)
-
-        env_args = {
-            "bddl_file_name": task_bddl_file,
-            "camera_heights": self.observation_height,
-            "camera_widths": self.observation_width,
-        }
-        env = OffScreenRenderEnv(**env_args)
-        env.reset()
-        return env
-
     def _format_raw_obs(self, raw_obs: RobotObservation) -> RobotObservation:
+        assert self._env is not None, "_format_raw_obs called before _ensure_env()"
         images = {}
         for camera_name in self.camera_name:
             image = raw_obs[camera_name]
@@ -294,6 +308,7 @@ class LiberoEnv(gym.Env):
         )
 
     def reset(self, seed=None, **kwargs):
+        self._ensure_env()
         super().reset(seed=seed)
         self._env.seed(seed)
         raw_obs = self._env.reset()
@@ -320,6 +335,8 @@ class LiberoEnv(gym.Env):
         return observation, info
 
     def step(self, action: np.ndarray) -> tuple[RobotObservation, float, bool, bool, dict[str, Any]]:
+        self._ensure_env()
+        assert self._env is not None
         if action.ndim != 1:
             raise ValueError(
                 f"Expected action to be 1-D (shape (action_dim,)), "
@@ -350,7 +367,8 @@ class LiberoEnv(gym.Env):
         return observation, reward, terminated, truncated, info
 
     def close(self):
-        self._env.close()
+        if self._env is not None:
+            self._env.close()
 
 
 def _make_env_fns(

src/lerobot/envs/metaworld.py

@@ -97,8 +97,9 @@ class MetaworldEnv(gym.Env):
         self.visualization_height = visualization_height
         self.camera_name = camera_name
 
-        self._env = self._make_envs_task(self.task)
+        self._env_name = self.task  # already stripped of "metaworld-" prefix above
-        self._max_episode_steps = self._env.max_path_length
+        self._env = None  # deferred — created on first reset() inside the worker subprocess
+        self._max_episode_steps = 500  # MT1 environments always have max_path_length=500
         self.task_description = TASK_DESCRIPTIONS[self.task]
 
         self.expert_policy = TASK_POLICY_MAPPING[self.task]()
@@ -136,6 +137,24 @@ class MetaworldEnv(gym.Env):
 
         self.action_space = spaces.Box(low=-1, high=1, shape=(ACTION_DIM,), dtype=np.float32)
 
+    def _ensure_env(self) -> None:
+        """Create the underlying MetaWorld env on first use.
+
+        Called inside the worker subprocess after fork(), so each worker gets
+        its own clean rendering context rather than inheriting a stale one from
+        the parent process (which causes crashes with AsyncVectorEnv).
+        """
+        if self._env is not None:
+            return
+        mt1 = metaworld.MT1(self._env_name, seed=42)
+        env = mt1.train_classes[self._env_name](render_mode="rgb_array", camera_name=self.camera_name)
+        env.set_task(mt1.train_tasks[0])
+        if self.camera_name == "corner2":
+            env.model.cam_pos[2] = [0.75, 0.075, 0.7]
+        env.reset()
+        env._freeze_rand_vec = False  # otherwise no randomization
+        self._env = env
+
     def render(self) -> np.ndarray:
         """
         Render the current environment frame.
@@ -143,26 +162,13 @@ class MetaworldEnv(gym.Env):
         Returns:
             np.ndarray: The rendered RGB image from the environment.
         """
+        self._ensure_env()
         image = self._env.render()
         if self.camera_name == "corner2":
             # Images from this camera are flipped — correct them
             image = np.flip(image, (0, 1))
         return image
 
-    def _make_envs_task(self, env_name: str):
-        mt1 = metaworld.MT1(env_name, seed=42)
-        env = mt1.train_classes[env_name](render_mode="rgb_array", camera_name=self.camera_name)
-        env.set_task(mt1.train_tasks[0])
-        if self.camera_name == "corner2":
-            env.model.cam_pos[2] = [
-                0.75,
-                0.075,
-                0.7,
-            ]  # corner2 position, similar to https://arxiv.org/pdf/2206.14244
-        env.reset()
-        env._freeze_rand_vec = False  # otherwise no randomization
-        return env
-
     def _format_raw_obs(self, raw_obs: np.ndarray) -> RobotObservation:
         image = None
         if self._env is not None:
@@ -209,6 +215,7 @@ class MetaworldEnv(gym.Env):
             observation (RobotObservation): The initial formatted observation.
             info (Dict[str, Any]): Additional info about the reset state.
         """
+        self._ensure_env()
         super().reset(seed=seed)
 
         raw_obs, info = self._env.reset(seed=seed)
@@ -232,6 +239,7 @@ class MetaworldEnv(gym.Env):
             truncated (bool): Whether the episode was truncated due to a time limit.
             info (Dict[str, Any]): Additional environment info.
         """
+        self._ensure_env()
         if action.ndim != 1:
             raise ValueError(
                 f"Expected action to be 1-D (shape (action_dim,)), "
@@ -263,7 +271,8 @@ class MetaworldEnv(gym.Env):
         return observation, reward, terminated, truncated, info
 
     def close(self):
-        self._env.close()
+        if self._env is not None:
+            self._env.close()
 
 
 # ---- Main API ----------------------------------------------------------------

src/lerobot/scripts/lerobot_eval.py

@@ -47,6 +47,7 @@ You can learn about the CLI options for this script in the `EvalPipelineConfig`
 """
 
 import concurrent.futures as cf
+import copy
 import json
 import logging
 import threading
@@ -56,7 +57,6 @@ from collections.abc import Callable
 from contextlib import nullcontext
 from copy import deepcopy
 from dataclasses import asdict
-from functools import partial
 from pathlib import Path
 from pprint import pformat
 from typing import Any, TypedDict
@@ -73,7 +73,6 @@ from lerobot.configs import parser
 from lerobot.configs.eval import EvalPipelineConfig
 from lerobot.envs.factory import make_env, make_env_pre_post_processors
 from lerobot.envs.utils import (
-    add_envs_task,
     check_env_attributes_and_types,
     close_envs,
     preprocess_observation,
@@ -166,9 +165,9 @@ def rollout(
         if return_observations:
             all_observations.append(deepcopy(observation))
 
-        # Infer "task" from attributes of environments.
+        # Infer "task" from sub-environments.
-        # TODO: works with SyncVectorEnv but not AsyncVectorEnv
+        # env.call() works with both SyncVectorEnv and AsyncVectorEnv.
-        observation = add_envs_task(env, observation)
+        observation["task"] = env.call("task")
 
         # Apply environment-specific preprocessing (e.g., LiberoProcessorStep for LIBERO)
         observation = env_preprocessor(observation)
@@ -734,34 +733,48 @@ def eval_policy_all(
             group_acc[group]["video_paths"].extend(paths)
             overall["video_paths"].extend(paths)
 
+    def _make_thread_policy(p: PreTrainedPolicy) -> PreTrainedPolicy:
+        """Shallow copy sharing weight tensors, with independent per-thread state.
+
+        copy.copy() gives a new Python object whose _parameters dict is a shared
+        reference (same tensor storage, zero extra VRAM). reset() then rebinds
+        mutable state (action queues etc.) to fresh per-thread objects.
+
+        Note: does NOT work for ACT with temporal_ensemble_coeff — that policy's
+        reset() mutates a shared sub-object. Use max_parallel_tasks=1 for that config.
+        """
+        thread_p = copy.copy(p)
+        thread_p.reset()
+        return thread_p
+
     # Choose runner (sequential vs threaded)
-    task_runner = partial(
+    _runner_kwargs = {
-        run_one,
+        "env_preprocessor": env_preprocessor,
-        policy=policy,
+        "env_postprocessor": env_postprocessor,
-        env_preprocessor=env_preprocessor,
+        "preprocessor": preprocessor,
-        env_postprocessor=env_postprocessor,
+        "postprocessor": postprocessor,
-        preprocessor=preprocessor,
+        "n_episodes": n_episodes,
-        postprocessor=postprocessor,
+        "max_episodes_rendered": max_episodes_rendered,
-        n_episodes=n_episodes,
+        "videos_dir": videos_dir,
-        max_episodes_rendered=max_episodes_rendered,
+        "return_episode_data": return_episode_data,
-        videos_dir=videos_dir,
+        "start_seed": start_seed,
-        return_episode_data=return_episode_data,
+    }
-        start_seed=start_seed,
-    )
 
     if max_parallel_tasks <= 1:
         # sequential path (single accumulator path on the main thread)
         # NOTE: keeping a single-threaded accumulator avoids concurrent list appends or locks
         for task_group, task_id, env in tasks:
-            tg, tid, metrics = task_runner(task_group, task_id, env)
+            tg, tid, metrics = run_one(task_group, task_id, env, policy=policy, **_runner_kwargs)
             _accumulate_to(tg, metrics)
             per_task_infos.append({"task_group": tg, "task_id": tid, "metrics": metrics})
     else:
-        # threaded path: submit all tasks, consume completions on main thread and accumulate there
+        # threaded path: each thread gets a shallow policy copy (shared weights, independent state)
         with cf.ThreadPoolExecutor(max_workers=max_parallel_tasks) as executor:
             fut2meta = {}
             for task_group, task_id, env in tasks:
-                fut = executor.submit(task_runner, task_group, task_id, env)
+                fut = executor.submit(
+                    run_one, task_group, task_id, env, policy=_make_thread_policy(policy), **_runner_kwargs
+                )
                 fut2meta[fut] = (task_group, task_id)
             for fut in cf.as_completed(fut2meta):
                 tg, tid, metrics = fut.result()

tests/envs/test_dispatch.py

@@ -0,0 +1,143 @@
+"""Tests for the benchmark dispatch refactor (create_envs / get_env_processors on EnvConfig)."""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass, field
+
+import gymnasium as gym
+import pytest
+from gymnasium.envs.registration import register, registry as gym_registry
+
+from lerobot.configs.types import PolicyFeature
+from lerobot.envs.configs import EnvConfig
+from lerobot.envs.factory import make_env, make_env_config, make_env_pre_post_processors
+
+logger = logging.getLogger(__name__)
+
+
+def test_registry_all_types():
+    """make_env_config should resolve every registered EnvConfig subclass via the registry."""
+    known = list(EnvConfig.get_known_choices().keys())
+    assert len(known) >= 6
+    for t in known:
+        cfg = make_env_config(t)
+        assert cfg.type == t
+
+
+def test_unknown_type():
+    with pytest.raises(ValueError, match="not registered"):
+        make_env_config("nonexistent")
+
+
+def test_identity_processors():
+    """Base class get_env_processors() returns identity pipelines."""
+    cfg = make_env_config("aloha")
+    pre, post = cfg.get_env_processors()
+    assert len(pre.steps) == 0 and len(post.steps) == 0
+
+
+def test_delegation():
+    """make_env() should call cfg.create_envs(), not use if/elif dispatch."""
+    sentinel = {"delegated": {0: "marker"}}
+    fake = type(
+        "Fake",
+        (),
+        {
+            "hub_path": None,
+            "create_envs": lambda self, n_envs, use_async_envs=False: sentinel,
+        },
+    )()
+    result = make_env(fake, n_envs=1)
+    assert result is sentinel
+
+
+def test_processors_delegation():
+    """make_env_pre_post_processors delegates to cfg.get_env_processors()."""
+    from lerobot.configs.policies import PreTrainedConfig
+
+    cfg = make_env_config("aloha")
+    pre, post = make_env_pre_post_processors(cfg, PreTrainedConfig())
+    assert len(pre.steps) == 0
+
+
+def test_base_create_envs():
+    """Base class create_envs() should build a single-task VectorEnv via gym.make()."""
+    gym_id = "_dispatch_test/CartPole-v99"
+    if gym_id not in gym_registry:
+        register(id=gym_id, entry_point="gymnasium.envs.classic_control:CartPoleEnv")
+
+    @EnvConfig.register_subclass("_dispatch_base_test")
+    @dataclass
+    class _Env(EnvConfig):
+        task: str = "CartPole-v99"
+        fps: int = 10
+        features: dict[str, PolicyFeature] = field(default_factory=dict)
+
+        @property
+        def package_name(self):
+            return "_dispatch_test"
+
+        @property
+        def gym_id(self):
+            return gym_id
+
+        @property
+        def gym_kwargs(self):
+            return {}
+
+    try:
+        envs = _Env().create_envs(n_envs=2)
+        assert "_dispatch_base_test" in envs
+        env = envs["_dispatch_base_test"][0]
+        assert isinstance(env, gym.vector.SyncVectorEnv)
+        assert env.num_envs == 2
+        env.close()
+    finally:
+        if gym_id in gym_registry:
+            del gym_registry[gym_id]
+
+
+def test_custom_create_envs_override():
+    """A custom EnvConfig subclass can override create_envs()."""
+    mock_vec = gym.vector.SyncVectorEnv([lambda: gym.make("CartPole-v1")])
+
+    @EnvConfig.register_subclass("_dispatch_custom_test")
+    @dataclass
+    class _Env(EnvConfig):
+        task: str = "x"
+        features: dict[str, PolicyFeature] = field(default_factory=dict)
+
+        @property
+        def gym_kwargs(self):
+            return {}
+
+        def create_envs(self, n_envs, use_async_envs=False):
+            return {"custom_suite": {0: mock_vec}}
+
+    try:
+        result = make_env(_Env(), n_envs=1)
+        assert "custom_suite" in result
+    finally:
+        mock_vec.close()
+
+
+def test_custom_get_env_processors_override():
+    """A custom EnvConfig subclass can override get_env_processors()."""
+    from lerobot.processor.pipeline import PolicyProcessorPipeline
+
+    @EnvConfig.register_subclass("_dispatch_proc_test")
+    @dataclass
+    class _Env(EnvConfig):
+        task: str = "x"
+        features: dict[str, PolicyFeature] = field(default_factory=dict)
+
+        @property
+        def gym_kwargs(self):
+            return {}
+
+        def get_env_processors(self):
+            return PolicyProcessorPipeline(steps=[]), PolicyProcessorPipeline(steps=[])
+
+    pre, post = _Env().get_env_processors()
+    assert isinstance(pre, PolicyProcessorPipeline)