Lifecycle
This section describes the different hooks that can be implemented by an operator and what their use case is.
Priority
Operators are initialized (PreStart and Start) according to their priority and they are closed (Stop, PreStop and Close) in the reverse order.
Lifecycle
Under the hood, Inspektor Gadget uses two separate functions that control these lifecycles. One is to get information from a gadget ("GetGadgetInfo"), one is to actually run a gadget ("RunGadget").
While the latter runs all lifecycle steps in the order documented below, the
former will only call Instantiate and Close. That means that everything you
do in Instantiate should use the least possible resources, but also that
everything a gadget "offers" should be known after that step. That means: all
DataSources should be known and finalized (fields added/modified, annotations
added, etc.) after this step.
Actual work should only be done on the forthcoming hooks (PreStart/Start).
If the initialization step needs to actually create some kind of state that is
necessary for later steps in the RunGadget case, the Close hook can be used
to tear everything back down.
Instantiate
Instances (DataOperatorInstance and ImageOperatorInstance) are created by
InstantiateDataOperator() and InstantiateImageOperator() respectively. Those
functions should return a new initalized instance of the operator. They can also
return nil if the operator should be skipped. Data sources should be created
in this step.
PreStart (optional)
The PreStart() method is called before the gadget is started. The operator can subscribe to existing data sources here.
Start
This method indicates the operator should start emitting data.
Stop
The operator shouldn't emit any other data after stop has been called.
PostStop (optional)
The PostStop() method is used to perform last minute operations after the operator has been stopped.
Close
The Close() method is called to shutdown the operator. It must release all resources and stop all operations started by the methods above.
ExtraParams (optional)
The ExtraParams() method is used to expose parameters to control the operator.