com.hazelcast.map.EntryProcessor Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2016, 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.map;
import java.io.Serializable;
import java.util.Map;
/**
* An EntryProcessor passes you a {@link java.util.Map.Entry}. At the time you receive it
* the entry is locked and not released until the EntryProcessor completes.
* This obviates the need to explicitly lock as would be required with a {@link java.util.concurrent.ExecutorService}.
*
* Performance can be very high as the data is not moved off the Member partition. This avoids network cost and, if
* the storage format is {@link com.hazelcast.config.InMemoryFormat#OBJECT}, then there is no de-serialization or serialization
* cost.
*
* EntryProcessors execute on the partition thread in a member. Multiple operations on the same partition are queued.
*
* While executing partition migrations are not allowed. Any migrations are queued on the partition thread.
*
* An EntryProcessor may not be re-entrant i.e. it may not access the same {@link Map}. Limitation: you can only access
* data on the same partition.
*
* Note that to modify an entry by using EntryProcessors you should explicitly call the
* {@link java.util.Map.Entry#setValue} method of {@link java.util.Map.Entry} such as:
*
*
*
* {@literal}Override
* public Object process(Map.Entry entry) {
* Value value = entry.getValue();
* // process and modify value
* // ...
* entry.setValue(value);
* return result;
* }
*
*
* otherwise EntryProcessor does not guarantee that it will modify the entry.
*
* EntryProcessor instances can be shared between threads. If an EntryProcessor instance contains mutable state, proper
* concurrency control needs to be provided to coordinate access to mutable state. Another option is to rely on threadlocals.
*
* @param Type of key of a {@link java.util.Map.Entry}
* @param Type of value of a {@link java.util.Map.Entry}
* @see AbstractEntryProcessor
*/
public interface EntryProcessor extends Serializable {
/**
* Process the entry without worrying about concurrency.
*
* Note that to modify an entry by using EntryProcessor you should explicitly call
* {@link java.util.Map.Entry#setValue} method of {@link java.util.Map.Entry} such as:
*
*
*
* {@literal}Override
* public Object process(Map.Entry entry) {
* Value value = entry.getValue();
* // process and modify value
* // ...
* entry.setValue(value);
* return result;
* }
*
*
* otherwise EntryProcessor does not guarantee to modify the entry.
*
* @param entry entry to be processed
* @return result of the process
*/
Object process(Map.Entry entry);
/**
* Get the entry processor to be applied to backup entries.
*
* In case of a readonly execution, null can be returned to indicate that no backups should be made.
*
* @return the back up processor
*/
EntryBackupProcessor getBackupProcessor();
}