/*
* Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved.
*
* 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.hazelcast.scheduledexecutor;
import java.util.Map;
import java.util.concurrent.Callable;
/**
* An interface to provide means for saving & loading state for {@link Runnable} and {@link java.util.concurrent.Callable}
* tasks scheduled with an {@link IScheduledExecutorService}. When task implements this interface, the Scheduled Executor
* will be able to handle state of the task among the replicas in an event of Migration or Node failure.
*
* Example:
* <pre>
* public class CleanUpTask implements Runnable, StatefulTask<String, Integer>, HazelcastInstanceAware {
*
* private transient HazelcastInstance instance;
*
* private transient int recordsDeletedSoFar;
*
* public CleanUpTask(HazelcastInstance instance) {
* this.instance = instance;
* }
*
* public void run() {
* recordsDeletedSoFar += cleanUpInvalidRecordsAndReturnCount();
* }
*
* private int cleanUpInvalidRecordsAndReturnCount() {
* }
*
* public void save(Map<String, Integer> snapshot) {
* snapshot.put("recordsDeletedSoFar", recordsDeletedSoFar);
* }
*
* public void load(Map<String, Integer> snapshot) {
* if (state.containsKey("recordsDeletedSoFar")) {
* recordsDeletedSoFar = snapshot.get("recordsDeletedSoFar");
* }
* }
* }
* </pre>
*
* @param <K> The data type of the Key in the state {@link Map}
* @param <V> The data type of the Value in the state {@link Map}
*/
public interface StatefulTask<K, V> {
/**
* Task callback to capture its state on the provided map.
* This is invoked after each invocation of {@link Runnable#run()} or {@link Callable#call()}
* to capture a snapshot of the state and publish to replicas. If two or more replicas of the
* same task run at the same time and publish their states, then only the one running on the owner
* member will be allowed to update the replicas.
*
* <b>Note: </b> The state of the cluster is not known or guaranteed during task's execution, thus,
* publication of the task's state to replicas is done on best-effort basis.
*
* Called immediately after run() or call() of the {@link Runnable}
* or {@link java.util.concurrent.Callable} respectively.
*
* @param snapshot The {@link Map} responsible for holding a snapshot of the current state.
*/
void save(Map<K, V> snapshot);
/**
* Task callback to initialize its inner state, after a replica promotion, from the given map.
* This is invoked once per task's lifecycle in a single member, before invocation of
* {@link Runnable#run()} or {@link Callable#call()} to setup task's state as published from
* the previous owner of the task in the cluster.
*
* <tt>load</tt> will not be called if the snapshot is empty.
*
* @param snapshot The {@link Map} responsible for providing a snapshot of the task's state.
*/
void load(Map<K, V> snapshot);
}