Fixes reference count in asset instances due to circular references (#580)

With the lazy buffer implementation in asset classes, we pass the
physics sim-view to the data object. This increments the reference count
of the sim-view instance and blocks the asset instance itself to be
garbage collected properly.

This MR takes steps to fix this issue.

## Type of change

- Bug fix (non-breaking change which fixes an issue)
- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have run all the tests with `./isaaclab.sh --test` and they pass
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

source/extensions/omni.isaac.lab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.18.3"
+version = "0.18.4"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/extensions/omni.isaac.lab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.18.4 (2024-06-26)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed double reference count of the physics sim view inside the asset classes. This was causing issues
+  when destroying the asset class instance since the physics sim view was not being properly released.
+
+Added
+^^^^^
+
+* Added the attribute :attr:`~omni.isaac.lab.assets.AssetBase.is_initialized` to check if the asset and sensor
+  has been initialized properly. This can be used to ensure that the asset or sensor is ready to use in the simulation.
+
+
 0.18.3 (2024-06-25)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py

@@ -88,6 +88,14 @@ class Articulation(RigidObject):
     cfg: ArticulationCfg
     """Configuration instance for the articulations."""
 
+    actuators: dict[str, ActuatorBase]
+    """Dictionary of actuator instances for the articulation.
+
+    The keys are the actuator names and the values are the actuator instances. The actuator instances
+    are initialized based on the actuator configurations specified in the :attr:`ArticulationCfg.actuators`
+    attribute. They are used to compute the joint commands during the :meth:`write_data_to_sim` function.
+    """
+
     def __init__(self, cfg: ArticulationCfg):
         """Initialize the articulation.
 
@@ -95,8 +103,6 @@ class Articulation(RigidObject):
             cfg: A configuration instance.
         """
         super().__init__(cfg)
-        # data for storing actuator group
-        self.actuators: dict[str, ActuatorBase] = dict.fromkeys(self.cfg.actuators.keys())
 
     """
     Properties
@@ -870,8 +876,10 @@ class Articulation(RigidObject):
         # -- properties
         self._data.joint_names = self.joint_names
 
+        # -- default joint state
         self._data.default_joint_pos = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.default_joint_vel = torch.zeros_like(self._data.default_joint_pos)
+
         # -- joint commands
         self._data.joint_pos_target = torch.zeros_like(self._data.default_joint_pos)
         self._data.joint_vel_target = torch.zeros_like(self._data.default_joint_pos)
@@ -881,9 +889,11 @@ class Articulation(RigidObject):
         self._data.joint_armature = torch.zeros_like(self._data.default_joint_pos)
         self._data.joint_friction = torch.zeros_like(self._data.default_joint_pos)
         self._data.joint_limits = torch.zeros(self.num_instances, self.num_joints, 2, device=self.device)
+
         # -- joint commands (explicit)
         self._data.computed_torque = torch.zeros_like(self._data.default_joint_pos)
         self._data.applied_torque = torch.zeros_like(self._data.default_joint_pos)
+
         # -- tendons
         if self.num_fixed_tendons > 0:
             self._data.fixed_tendon_stiffness = torch.zeros(
@@ -907,12 +917,15 @@ class Articulation(RigidObject):
         self._data.soft_joint_pos_limits = torch.zeros(self.num_instances, self.num_joints, 2, device=self.device)
         self._data.soft_joint_vel_limits = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.gear_ratio = torch.ones(self.num_instances, self.num_joints, device=self.device)
-        # -- initialize default buffers
+
+        # -- initialize default buffers related to joint properties
         self._data.default_joint_stiffness = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.default_joint_damping = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.default_joint_armature = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.default_joint_friction = torch.zeros(self.num_instances, self.num_joints, device=self.device)
         self._data.default_joint_limits = torch.zeros(self.num_instances, self.num_joints, 2, device=self.device)
+
+        # -- initialize default buffers related to fixed tendon properties
         if self.num_fixed_tendons > 0:
             self._data.default_fixed_tendon_stiffness = torch.zeros(
                 self.num_instances, self.num_fixed_tendons, device=self.device
@@ -963,6 +976,7 @@ class Articulation(RigidObject):
         )
         self._data.default_joint_vel[:, indices_list] = torch.tensor(values_list, device=self.device)
 
+        # -- joint limits
         self._data.default_joint_limits = self.root_physx_view.get_dof_limits().to(device=self.device).clone()
         self._data.joint_limits = self._data.default_joint_limits.clone()
 
@@ -972,9 +986,12 @@ class Articulation(RigidObject):
 
     def _process_actuators_cfg(self):
         """Process and apply articulation joint properties."""
+        # create actuators
+        self.actuators = dict()
         # flag for implicit actuators
         # if this is false, we by-pass certain checks when doing actuator-related operations
         self._has_implicit_actuators = False
+
         # cache the values coming from the usd
         usd_stiffness = self.root_physx_view.get_dof_stiffnesses().clone()
         usd_damping = self.root_physx_view.get_dof_dampings().clone()
@@ -982,6 +999,7 @@ class Articulation(RigidObject):
         usd_friction = self.root_physx_view.get_dof_friction_coefficients().clone()
         usd_effort_limit = self.root_physx_view.get_dof_max_forces().clone()
         usd_velocity_limit = self.root_physx_view.get_dof_max_velocities().clone()
+
         # iterate over all actuator configurations
         for actuator_name, actuator_cfg in self.cfg.actuators.items():
             # type annotation for type checkers

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation_data.py

@@ -21,7 +21,12 @@ class ArticulationData(RigidObjectData):
     """
 
     _root_physx_view: physx.ArticulationView
-    """The root articulation view of the object."""
+    """The root articulation view of the object.
+
+    Note:
+        Internally, this is stored as a weak reference to avoid circular references between the asset class
+        and the data container. This is important to avoid memory leaks.
+    """
 
     def __init__(self, root_physx_view: physx.ArticulationView, device: str):
         # Initialize the parent class

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/asset_base.py

@@ -120,6 +120,14 @@ class AssetBase(ABC):
     Properties
     """
 
+    @property
+    def is_initialized(self) -> bool:
+        """Whether the asset is initialized.
+
+        Returns True if the asset is initialized, False otherwise.
+        """
+        return self._is_initialized
+
     @property
     @abstractmethod
     def num_instances(self) -> int:

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/rigid_object/rigid_object.py

@@ -76,7 +76,7 @@ class RigidObject(AssetBase):
 
     @property
     def body_names(self) -> list[str]:
-        """Ordered names of bodies in articulation."""
+        """Ordered names of bodies in the rigid object."""
         prim_paths = self.root_physx_view.prim_paths[: self.num_bodies]
         return [path.split("/")[-1] for path in prim_paths]
 
@@ -340,6 +340,7 @@ class RigidObject(AssetBase):
         self._external_force_b = torch.zeros((self.num_instances, self.num_bodies, 3), device=self.device)
         self._external_torque_b = torch.zeros_like(self._external_force_b)
 
+        # set information about rigid body into data
         self._data.body_names = self.body_names
         self._data.default_mass = self.root_physx_view.get_masses().clone()
 

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/rigid_object/rigid_object_data.py

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 import torch
+import weakref
 
 import omni.physics.tensors.impl.api as physx
 
@@ -24,7 +25,12 @@ class RigidObjectData:
     """
 
     _root_physx_view: physx.RigidBodyView
-    """The root rigid body view of the object."""
+    """The root rigid body view of the object.
+
+    Note:
+        Internally, this is stored as a weak reference to avoid circular references between the asset class
+        and the data container. This is important to avoid memory leaks.
+    """
 
     def __init__(self, root_physx_view: physx.RigidBodyView, device: str):
         """Initializes the rigid object data.
@@ -35,7 +41,7 @@ class RigidObjectData:
         """
         # Set the parameters
         self.device = device
-        self._root_physx_view = root_physx_view
+        self._root_physx_view = weakref.proxy(root_physx_view)  # weak reference to avoid circular references
         # Set initial time stamp
         self._sim_timestamp = 0.0
 

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/manager_based_env.py

@@ -308,11 +308,11 @@ class ManagerBasedEnv:
         """Cleanup for the environment."""
         if not self._is_closed:
             # destructor is order-sensitive
+            del self.viewport_camera_controller
             del self.action_manager
             del self.observation_manager
             del self.event_manager
             del self.scene
-            del self.viewport_camera_controller
             # clear callbacks and instance
             self.sim.clear_all_callbacks()
             self.sim.clear_instance()

source/extensions/omni.isaac.lab/omni/isaac/lab/sensors/sensor_base.py

@@ -92,6 +92,14 @@ class SensorBase(ABC):
     Properties
     """
 
+    @property
+    def is_initialized(self) -> bool:
+        """Whether the sensor is initialized.
+
+        Returns True if the sensor is initialized, False otherwise.
+        """
+        return self._is_initialized
+
     @property
     def num_instances(self) -> int:
         """Number of instances of the sensor.

source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/manager_based/classic/humanoid/mdp/observations.py

@@ -50,7 +50,7 @@ def base_heading_proj(
     to_target_pos[:, 2] = 0.0
     to_target_dir = math_utils.normalize(to_target_pos)
     # compute base forward vector
-    heading_vec = math_utils.quat_rotate(asset.data.root_quat_w, asset.data.forward_vec_b)
+    heading_vec = math_utils.quat_rotate(asset.data.root_quat_w, asset.data.FORWARD_VEC_B)
     # compute dot product between heading and target direction
     heading_proj = torch.bmm(heading_vec.view(env.num_envs, 1, 3), to_target_dir.view(env.num_envs, 3, 1))