OrderedShutdownHooks.java
/*
** Module : OrderedShutdownHooks.java
** Abstract : Manages registered shutdown hooks in a prioritized order during JVM shutdown.
**
** Copyright (c) 2024-2025, Golden Code Development Corporation.
**
** -#- -I- --Date-- ---------------------------------Description----------------------------------
** 001 ICP 20240722 First version.
** 002 GBB 20250403 Refactoring, removing misleadingly named method getInstance.
*/
/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
**
** Additional terms under GNU Affero GPL version 3 section 7:
**
** Under Section 7 of the GNU Affero GPL version 3, the following additional
** terms apply to the works covered under the License. These additional terms
** are non-permissive additional terms allowed under Section 7 of the GNU
** Affero GPL version 3 and may not be removed by you.
**
** 0. Attribution Requirement.
**
** You must preserve all legal notices or author attributions in the covered
** work or Appropriate Legal Notices displayed by works containing the covered
** work. You may not remove from the covered work any author or developer
** credit already included within the covered work.
**
** 1. No License To Use Trademarks.
**
** This license does not grant any license or rights to use the trademarks
** Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
** of Golden Code Development Corporation. You are not authorized to use the
** name Golden Code, FWD, or the names of any author or contributor, for
** publicity purposes without written authorization.
**
** 2. No Misrepresentation of Affiliation.
**
** You may not represent yourself as Golden Code Development Corporation or FWD.
**
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** Golden Code Development Corporation, FWD, or any author or contributor to
** the covered work, without written authorization.
**
** 3. No Misrepresentation of Source or Origin.
**
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** versions of the covered work must be marked in a reasonable way to make it
** clear that the modified work is not originating from Golden Code Development
** Corporation or FWD. All modified versions must contain the notices of
** attribution required in this license.
*/
package com.goldencode.p2j.main;
import com.goldencode.p2j.util.logging.CentralLogger;
import java.util.*;
/**
* This class ensures that registered hooks are run in a specified order of priority when the JVM shuts down.
* It uses a singleton pattern to maintain a single instance and a list of hooks that are sorted and executed
* based on their priority.
* The shutdown hooks are executed automatically when the JVM shuts down.
*/
public class OrderedShutdownHooks
{
/** Logger. */
private static final CentralLogger LOG = CentralLogger.get(OrderedShutdownHooks.class);
/** Singleton instance */
private static Thread shutdownHook = null;
/** List of hooks to be handled at server shutdown */
private static final List<ShutdownHook> shutdownHooks = new ArrayList<>();
/**
* Class representing a shutdown hook. Each shutdown hook has a priority level
* that determines the order of execution, with lower priority values executed first.
* It also includes a {@link Runnable} action that defines the task to be performed during shutdown.
*/
private static class ShutdownHook
{
/** The priority level of the shutdown hook */
int priority;
/** The action to be executed during shutdown */
Runnable action;
/**
* Constructs a new ShutdownHook with the specified priority level and action.
*
* @param priority
* The priority level of the shutdown hook.
* @param action
* The action to be executed during shutdown.
*/
ShutdownHook(int priority, Runnable action)
{
this.priority = priority;
this.action = action;
}
/**
* Compare two instances.
*
* @param obj
* An object to compare with.
*
* @return <code>true</code> if the two are identical.
*/
@Override
public boolean equals(Object obj)
{
if (this == obj) return true;
if (obj == null || getClass() != obj.getClass())
{
return false;
}
ShutdownHook that = (ShutdownHook) obj;
return priority == that.priority && Objects.equals(action, that.action);
}
/**
* Calculate hash code
*
* @return hash code
*/
@Override
public int hashCode()
{
return Objects.hash(priority, action);
}
}
/**
* Private constructor to prevent instantiation from outside the class.
*/
private OrderedShutdownHooks()
{
}
/**
* Registers a new shutdown hook with a specified priority.
* The hooks will be executed in ascending order of their priority values.
*
* @param priority
* The priority of the shutdown hook.
* @param action
* The {@link Runnable} action to be executed during shutdown.
*/
public static synchronized void registerShutdownHook(int priority, Runnable action)
{
if (shutdownHook == null)
{
shutdownHook = new Thread(OrderedShutdownHooks::executeShutdownHooks);
Runtime.getRuntime().addShutdownHook(shutdownHook);
}
shutdownHooks.add(new ShutdownHook(priority, action));
}
/**
* Deregisters a shutdown hook with a specified priority.
*
* @param priority
* The priority of the shutdown hook.
* @param action
* The {@link Runnable} action to be executed during shutdown.
*/
public static synchronized void deregisterShutdownHook(int priority, Runnable action)
{
shutdownHooks.remove(new ShutdownHook(priority, action));
}
/**
* Executes all registered shutdown hooks in the order of their priority.
* Hooks with lower priority values are executed first.
*/
private static synchronized void executeShutdownHooks()
{
shutdownHooks.stream()
.sorted(Comparator.comparingInt(hook -> hook.priority))
.forEach(hook ->
{
try
{
hook.action.run();
}
catch (Exception e)
{
LOG.severe("Error while running shutdown hook.", e);
}
});
}
}