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OperatorState.java
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OperatorState.java
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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.flink.api.common.state;
import java.io.IOException;
import org.apache.flink.api.common.functions.MapFunction;
/**
* Base interface for all streaming operator states. It can represent both
* partitioned (when state partitioning is defined in the program) or
* non-partitioned user states.
*
* State can be accessed and manipulated using the {@link #value()} and
* {@link #update(T)} methods. These calls are only safe in the
* transformation call the operator represents, for instance inside
* {@link MapFunction#map()} and can lead tp unexpected behavior in the
* {@link #open(org.apache.flink.configuration.Configuration)} or
* {@link #close()} methods.
*
* @param <T>
* Type of the operator state
*/
public interface OperatorState<T> {
/**
* Returns the current value for the state. When the state is not
* partitioned the returned value is the same for all inputs in a given
* operator instance. If state partitioning is applied, the value returned
* depends on the current operator input, as the operator maintains an
* independent state for each partition.
*
* @return The operator state value corresponding to the current input.
*
* @throws IOException Thrown if the system cannot access the state.
*/
T value() throws IOException;
/**
* Updates the operator state accessible by {@link #value()} to the given
* value. The next time {@link #value()} is called (for the same state
* partition) the returned state will represent the updated value. When a
* partitioned state is updated with null, the state for the current key
* will be removed and the default value is returned on the next access.
*
* @param state
* The new value for the state.
*
* @throws IOException Thrown if the system cannot access the state.
*/
void update(T value) throws IOException;
}