Engine Node

class eagerx.core.entities.EngineNode(params, *args, simulator=None, message_broker=None, **kwargs)[source]

Baseclass for nodes that are only to be used in combination with a specific engine.

Users must call make() to make the engine node subclass’ specification.

Use this baseclass to implement nodes that will be added to an EngineGraph when specifying an engine implementation for an Object.

These nodes can, optionally, be synchronized with respect to the simulator clock by registering “tick” as an input.

Note

Engine nodes only receive a reference to the simulator as an argument to initialize() when the engine nodes are launched within the same process as the engine. See process for more info.

Subclasses must implement the following methods:

make()
initialize()
reset()
callback()
shutdown() (optional)

Use baseclass Node instead, for nodes that will be added to the (agnostic) Graph.

Use baseclass ResetNode instead, for reset routines.

abstract callback(t_n, **inputs)[source]

An abstract method that is called at the specified node rate.

This method should be decorated with:

eagerx.core.register.inputs() to register the inputs.
eagerx.core.register.outputs() to register the outputs.

Parameters

t_n (float) – Time passed (seconds) since last reset. Increments with 1/rate.
inputs (Msg) – Inputs that were registered (& selected) with the eagerx.core.register.inputs() decorator by the subclass.

Return type

Dict[str, Any]

Returns

Dictionary with outputs that were registered (& selected) with the eagerx.core.register.outputs() decorator by the subclass.

classmethod info(method=None)

A helper method to get info on a method of the specified subclass.

Parameters: method (Union[List[str], str, None]) – The registered method we would like to receive info on. If no method is specified, it provides info on the class itself.
Return type: str
Returns: Info on the subclass’ method.

abstract initialize(spec, simulator)[source]

An abstract method that initializes the node at run-time.

Parameters

spec (NodeSpec) – Specification of the engine node.
simulator (Any) – A reference to the simulator. The simulator type depends on the engine. Only available if the node was launched inside the engine process.

Return type

None

abstract classmethod make(*args, **kwargs)

An abstract method that makes the specification (also referred to as spec) of this entity.

Parameters

args (Any) – Arguments to the subclass’ make function.
kwargs (Any) – Optional Arguments to the subclass’ make function.

Returns

A (mutable) spec that can be used to build and subsequently initialize the entity (e.g. node, engine, …).

abstract reset(**states)[source]

An abstract method that resets the node to its initial state before the start of an episode.

This method should be decorated with eagerx.core.register.states() to register the states.

Warning

Avoid defining states for engine nodes, as you risk making your Object non-agnostic to the environment. Instead, try to implement object states as an EngineState of an Object.

Parameters: states (Any) – States that were registered (& selected) with the eagerx.core.register.states() decorator by the subclass. The state messages are sent by the environment and can be used to reset the node at the start of an episode. This can be anything from an estimator’s initial state to a hyper-parameter (e.g. delay, control gains).
Return type: None

set_delay(delay, component, cname)

A method to vary the delay of an input or feedthrough.

Parameters

delay (float) – A non-negative delay that can be varied at the beginning of an episode (during the reset procedure).
component (str) – Either “inputs” or “feedthroughs”.
cname (str) – name of the component.

Return type

None

shutdown()

A method that can be overwritten to cleanly shutdown (e.g. release resources).

Return type: None

backend: eagerx.core.entities.Backend: Responsible for all I/O communication within this process. Nodes inside the same process share the same message broker. Cannot be modified.

color: str: Specifies the color of logged messages & node color in the GUI. Check-out the termcolor documentation for the supported colors. Can be set in the subclass’ spec().

entity_id: str: A unique entity_id with the structure <module>/<classname>.

inputs: dict: Parameters for all selected inputs.

log_level: int: Specifies the log level for this node: {0: SILENT, 10: DEBUG, 20: INFO, 30: WARN, 40: ERROR, 50: FATAL}. Can be set in the subclass’ spec().

log_memory: int: Specifies the log level for logging memory usage over time for this node: {0: SILENT, 10: DEBUG, 20: INFO, 30: WARN, 40: ERROR, 50: FATAL}. Note that log_level has precedent over the memory level set here. Can be set in the subclass’ spec().

name: str: User specified node name. Can be set in spec().

ns: str: Namespace of the environment. Can be set with the name argument to BaseEnv.

outputs: dict: Parameters for all selected outputs.

process: int: Process in which this node is launched. See process for all options. Can be set in the subclass’ spec().

rate: float: Rate (Hz) at which the callback is called. Can be set in the subclass’ spec().

real_time_factor: float: A specified upper bound on the real_time factor. Wall-clock rate=real_time_factor*rate. If real_time_factor < 1 the simulation is slower than real time. Can be set in the engine’s spec().

simulate_delays: bool: Flag that specifies whether input delays are simulated. You probably want to set this to False when running in the real-world. Can be set in the engine’s spec().

states: dict: Parameters for all selected states.

sync: bool: Flag that specifies whether we run reactive or asynchronous. Can be set in the engine’s spec().