Execution and Callbacks

There are two components that control the execution of callbacks: executors and callback groups.

Executors are responsible for the actual execution of callbacks and should extend the Executor class.

Callback groups are used to enforce concurrency rules for callbacks and should extend the CallbackGroup class.

Executors

Callback Groups

class rclpy.callback_groups.CallbackGroup

The base class for a callback group.

A callback group controls when callbacks are allowed to be executed.

This class should not be instantiated. Instead, classes should extend it and implement can_execute(), beginning_execution(), and ending_execution().

add_entity(entity: Entity) → None

Add an entity to the callback group.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.

beginning_execution(entity: Entity) → bool

Get permission for the callback from the group to begin executing an entity.

If this returns True then CallbackGroup.ending_execution() must be called after the callback has been executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the callback can be executed, False otherwise.

can_execute(entity: Entity) → bool

Determine if an entity can be executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the entity can be executed, False otherwise.

ending_execution(entity: Entity) → None

Notify group that a callback has finished executing.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.

has_entity(entity: Entity) → bool

Determine if an entity has been added to this group.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.

class rclpy.callback_groups.MutuallyExclusiveCallbackGroup

Allow only one callback to be executing at a time.

beginning_execution(entity: Entity) → bool

Get permission for the callback from the group to begin executing an entity.

If this returns True then CallbackGroup.ending_execution() must be called after the callback has been executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the callback can be executed, False otherwise.

can_execute(entity: Entity) → bool

Determine if an entity can be executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the entity can be executed, False otherwise.

ending_execution(entity: Entity) → None

Notify group that a callback has finished executing.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.

class rclpy.callback_groups.ReentrantCallbackGroup

Allow callbacks to be executed in parallel without restriction.

beginning_execution(entity: Entity) → Literal[True]

Get permission for the callback from the group to begin executing an entity.

If this returns True then CallbackGroup.ending_execution() must be called after the callback has been executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the callback can be executed, False otherwise.

can_execute(entity: Entity) → Literal[True]

Determine if an entity can be executed.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.
Returns:: True if the entity can be executed, False otherwise.

ending_execution(entity: Entity) → None

Notify group that a callback has finished executing.

Parameters:: entity – a subscription, timer, client, service, or waitable instance.