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Split executors and (subscription) callbacks

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This commit is contained in:
Christophe Bedard 2019-05-27 09:40:04 +02:00
parent 48233c709e
commit efa3e7bbff
1 changed files with 34 additions and 28 deletions
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doc/ros_2.md
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@ -43,13 +43,13 @@ This parent constructor will allocate its own `rcl_node_t` handle and call `rcl_
```mermaid
sequenceDiagram
participant process
participant component
participant Component
participant rclcpp
participant rcl
participant rmw
process->>component: Component()
component->>rclcpp: : Node()
process->>Component: Component()
Component->>rclcpp: : Node()
Note over rclcpp: allocates rcl_node_t handle
rclcpp->>rcl: rcl_node_init()
Note over rcl: checks node name/namespace
@ -66,13 +66,12 @@ If intra-process publishing/subscription is enabled, it will be set up after cre
```mermaid
sequenceDiagram
participant component
participant Component
participant rclcpp
participant rcl
participant rmw
component->>rclcpp: create_publisher()
Note over rclcpp: through a lot of interfaces
Component->>rclcpp: create_publisher()
Note over rclcpp: allocates rcl_publisher_t handle
rclcpp->>rcl: rcl_publisher_init()
Note over rcl: populates rcl_publisher_t
@ -94,12 +93,12 @@ If intra-process publishing/subscription is enabled, it will be set up after cre
```mermaid
sequenceDiagram
participant component
participant Component
participant rclcpp
participant rcl
participant rmw
component->>rclcpp: create_subscription()
Component->>rclcpp: create_subscription()
Note over rclcpp: allocates rcl_subscription_t handle
rclcpp->>rcl: rcl_subscription_init()
Note over rcl: populates rcl_subscription_t
@ -111,7 +110,7 @@ sequenceDiagram
end
```
### Executors and callbacks
### Executors
An `rclcpp::executor::Executor` object is created for a given process. It can be a `SingleThreadedExecutor` or a `MultiThreadedExecutor`.
@ -119,31 +118,38 @@ Components are instanciated, usually as a `shared_ptr` through `std::make_shared
After all the components have been added, `Executor::spin()` is called. `SingleThreadedExecutor::spin()` simply loops forever until the process' context isn't valid anymore. It fetches the next `rclcpp::AnyExecutable` (e.g. subscription, timer, service, client), and calls `Executor::execute_any_executable()` with it. This then calls the relevant `execute*()` method (e.g. `execute_timer()`, `execute_subscription()`, `execute_intra_process_subscription()`, `execute_service()`, `execute_client()`).
```mermaid
sequenceDiagram
participant process
participant Executor
process->>Executor: Executor()
Note over process: instanciates components
process->>Executor: add_node(component)
process->>Executor: spin()
loop until shutdown
Note over Executor: get_next_executable()
Note over Executor: execute_any_executable()
Note over Executor: execute_*()
end
```
### Subscription callbacks
For subscriptions, callbacks are wrapped by an `rclcpp::AnySubscriptionCallback` object, which is registered when creating the `rclcpp::Subscription` object. Subscriptions are handled in the `rclcpp` layer.
In `execute_*subscription()`, the `Executor` allocates a message and calls `rcl_take()`. If that is successful, it then passes that on to the subscription through `rclcpp::SubscriptionBase::handle_message()`. Finally, this calls `dispatch()` on the `rclcpp::AnySubscriptionCallback` object, which calls the actual `std::function` with the right signature.
<!-- TODO sequenceDiagram -->
```mermaid
sequenceDiagram
participant process
participant executor
participant subscription
participant anycallback
participant Executor
participant Subscription
participant AnySubscriptionCallback
participant rcl
process->>executor: Executor()
Note over process: instanciates components
process->>executor: add_node(component)
process->>executor: spin()
loop until shutdown
Note over executor: get_next_executable()
Note over executor: execute_any_executable()
Note over executor: execute_subscription()
executor->>rcl: rcl_take()
executor->>subscription: handle_message()
subscription->>anycallback: dispatch()
Note over anycallback: std::function::operator(...)
end
Note over Executor: execute_subscription()
Executor->>rcl: rcl_take()
Executor->>Subscription: handle_message()
Subscription->>AnySubscriptionCallback: dispatch()
Note over AnySubscriptionCallback: std::function::operator(...)
```