com.google.cloud.dataflow.sdk.util.state.StateInternals Maven / Gradle / Ivy
/*
* Copyright (C) 2015 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.cloud.dataflow.sdk.util.state;
/**
* {@code StateInternals} describes the functionality a runner needs to provide for the
* State API to be supported.
*
* The SDK will only use this after elements have been partitioned by key. For instance, after a
* {@code GroupByKey} operation. The runner implementation must ensure that any writes using
* {@code StaeIntetrnals} are implicitly scoped to the key being processed and the specific step
* accessing state.
*
*
The runner implementation must also ensure that any writes to the associated state objects
* are persisted together with the completion status of the processing that produced these
* writes.
*
*
This is a low-level API intended for use by the Dataflow SDK. It should not be
* used directly, and is highly likely to change.
*/
public interface StateInternals {
/**
* Return the state associated with {@code address} in the specified {@code namespace}.
*/
T state(StateNamespace namespace, StateTag address);
/**
* Return state that reads from all the source namespaces. Only required to ensure that
* resultNamespace contains all the data that is added.
*
* Merging state is potentially destructive, in that it may move information from the
* {@code sourceNamespaces} to {@code resultNamespace}. As a result, after calling this all
* future calls should include as their namespaces a superset of
* {@code sourceNamespaces} and {@code resultNamespace}.
*/
> T mergedState(
Iterable sourceNamespaces, StateNamespace resultNamespace,
StateTag address);
}