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GppPlugin

As you may already know (see the concept), we call all plugins loaded by the GppPlugin as its child-plugins and group those child-plugins in three groups (pre-, global-, and post-planning groups).

Now its time to understand how each group is executed.

for plugin in plugins:
    success = plugin.run()
    if(!success && plugin.on_failure_break):
        return False
    elif(success && plugin.on_success_break):
        return True
return default_value

Above is a pythonic pseudo-code, showing the loop for each plugin-group. The "plugin" above has three attributes - the method run in line 2, which is just pseudo-code for executing the plugin. Additionally it has the members on_success_break and on_failure_break (lines 3 and 5). These members are specific to every child-plugin and allow you to customize the behavior of your pipeline. You may have "optional" child-plugins or might be satisfied if only one child-plugins returns a successful result.
Finally there is a third unknown value: default_value at the last line. This boolean value allows you to specify for each group what should happen, if the for-loop runs through without "preemptive" termination.

Behavior-Tree-Relation

You may set all the on_failure_break, on_success_break and default_value freely. Nonetheless, it's maybe important to highlight that you can implement sequence and selector nodes known from behavior-trees with the mentioned parameters.

If all child-plugins within one group have on_success_break set to true, on_failure_break. set to false and the default_value set to true, you will get a sequence-node. If you invert the values, the group will behave as a selector-node.

flag sequence selector
on_failure_break true false
on_success_break false true
default_value true false

Parameters

Now its time to look at how to define and load child-plugins and groups. The groups begin with the tags pre_planning, planning and post_planning. The child-plugins for those groups must be defined as a list. The order within this list defines later on the order of the execution. Every child-plugin in these lists must have a type and name tag. Additionally you can pass boolean on_failure_break and on_success_break. Finally you may provide a boolean default_value for each group.

Below an example

pre_planning:
    - {name: foo, type: bar, on_failure_break: True, on_success_break: False}
    - {name: baz, type: bum, on_failure_break: True, on_success_break: False}

pre_planning_default_value: True

We load in our pre-planning group two child-plugins with the names foo and baz. The on_failure_break, on_success_break and default_value are chosen such that the groups acts as a sequence node.

Below the detailed documentation. The <pre_planning|planning|post_planning> tag means here, that you can define the parameter under each of those groups.

~<name>/<pre_planning|planning|post_planning> (list)

List, as defined above.

~<name>/<pre_planning|planning|post_planning>/name (string)

Name of the plugin. The name will be passed to the child-plugin.

~<name>/<pre_planning|planning|post_planning>/type (string)

Type of the plugin. For the pre_planning group it must be resolvable to a plugin implementing the gpp_interface::PrePlanningInterface. For the planning group must be resolvable to a plugin implementing either nav_core::BaseGlobalPlanner or mbf_costmap_core::CostmapPlanner. For the post_planning group it must be resolvable to a plugin implementing the gpp_interface::PostPlanningInterface.

~<name>/<pre_planning|planning|post_planning>/on_failure_break (bool, true)

Value defining if the group should break its execution if this child-plugin fails.

~<name>/<pre_planning|planning|post_planning>/on_succuss_break (bool, false)

Value defining if the group should break its execution if this child-plugin succeeds.

~<name>/<pre_planning|planning|post_planning>_default_value (bool, true)

Default outcome of the group.

Example

Now we put the things together and create a dummy example for the GppPlugin. It assumes you are u

# this is for move-base-flex.
plugins:
    - {name: gpp_plugin, type: gpp_plugin::GppPlugin}

gpp_plugin:
    # we first define the pre_planning group. lets say all child-plugins are
    # optional and we may continue even if all child-plugins fail.
    pre_planning:
        - {name: pre_planner_name1, type: pre_planner_type1, on_failure_break: false}
        - {name: pre_planner_name2, type: pre_planner_type2, on_failure_break: false}
    pre_planning_default_value: True
    # now we define the planning group: we run both planners and take the first
    # successful result. if all planners fail, we fail
    planning:
        - {name: planner_name1, type: planner_type1, on_failure_break: false, on_success_break: true}
        - {name: planner_name2, type: planner_type2, on_failure_break: false, on_success_break: true}
    planning_default_value: False
    # finally the pose_planning group: we say that the post_planner_name1 is required,
    # the post_planner_name2 is optional.
    post_planning:
        - {name: post_planner_name1, type: post_planner_type1, on_failure_break: true}
        - {name: post_planner_name2, type: post_planner_type2, on_failure_break: false}
    pose_planning_default_value: True