org.apache.flink.statefun.sdk

Interface StatefulFunction

All Known Implementing Classes:

StatefulMatchFunction

public interface StatefulFunction

A StatefulFunction is a user-defined function that can be invoked with a given input. This is the primitive building block for a Stateful Functions application.

Concept

Each individual StatefulFunction is an uniquely invokable "instance" of a FunctionType. Each function is identified by an Address, representing the function's unique id (a string) within its type. From a user's perspective, it would seem as if for each unique function id, there exists a stateful instance of the function that is always available to be invoked within a Stateful Functions application.

Invoking a StatefulFunction

An individual StatefulFunction can be invoked with arbitrary input from any another StatefulFunction (including itself), or routed from ingresses via a Router. To invoke a StatefulFunction, the caller simply needs to know the Address of the target function.

As a result of invoking a StatefulFunction, the function may continue to invoke other functions, modify its state, or send messages to egresses addressed by an EgressIdentifier.

State

Each individual StatefulFunction may have state that is maintained by the system, providing exactly-once guarantees. Below is a code example of how to register and access state in functions:

 public class MyFunction implements StatefulFunction {

     {@code @Persisted}
     PersistedValue<Integer> intState = PersistedValue.of("state-name", Integer.class);

     {@code @Override}
     public void invoke(Context context, Object input) {
         Integer stateValue = intState.get();
         //...
         intState.set(1108);
         // send messages using context
     }
 }
 

See Also:

Address, FunctionType, Persisted, PersistedValue

Method Summary

Modifier and Type	Method and Description
void	invoke(Context context, java.lang.Object input) Invokes this function with a given input.

Method Detail

invoke

void invoke(Context context,
            java.lang.Object input)

Invokes this function with a given input.

Parameters:

context - context for the current invocation. The provided context instance should not be used outside the scope of the current invocation.

input - input for the current invocation.