# DeferredDeletablesManager.java

    /*
    ** Module   : DeferredDeletablesManager.java
    ** Abstract : Defines a manager for deletables which postpones them to a specific block.
    **
    ** Copyright (c) 2020-2023, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- ---------------------------------------Description----------------------------------------
    ** 001 AIL 20200518 Created initial version.
    **     AIL 20200616 Moved buffer logic to the procedure manager. Remade the getHandlingBlock().
    **     AIL 20200617 Moved the StaleProcedureHelper as separate class.
    **                  Javadoc update.
    ** 002 CA  20220120 Improved performance for finalizables, keep them already sorted by their weight.
    **     CA  20221006 Check if 'block.finalizables' exists before iterating it.  Refs #6824
    ** 003 CA  20231216 Avoid iterators when processing BlockDefinition.finalizables.
    */
    /*
    ** 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.
    **
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    **
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    **
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    */

    package com.goldencode.p2j.util;

    import java.util.*;

    /**
     * Provides a mean of postponing deletion of deletable resources at a specific block level. This is useful
     * where there are postpone deletes which can't be determined at the target place of deletion.
     */
    public class DeferredDeletablesManager
    implements Finalizable
    {
       /** The core collection of resources which are to be deleted when the manager is finished */
       private final Set<DeferredDeletable> deletables = new HashSet<>();

       /**
        * Registers a resource at a specific block depth. This also handles the scenario in which there
        * is already such manager registered at that block.
        *
        * @param     blockDepth
        *            The index of the outermost block at which a manager should be registered; blockDepth 0
        *            means the global scope.
        * @param     resource
        *            The resource which is to be registered.
        *
        * @return    <code>false</code> if the registration was skipped as this resource was already registered,
        *            <code>true</code> otherwise.
        */
       public static boolean registerAt(int blockDepth, DeferredDeletable resource)
       {
          BlockDefinition block = TransactionManager.getBlockAtDepth(blockDepth);

          Set<Finalizable>[] fini = block.finalizables;
          if (fini != null)
          {
             for (int i = 0; i < fini.length; i++)
             {
                Set<Finalizable> l = fini[i];

                if (l == null)
                {
                   continue;
                }

                for (Finalizable finalizable : l)
                {
                   if (finalizable instanceof DeferredDeletablesManager)
                   {
                      return ((DeferredDeletablesManager) finalizable).register(resource);
                   }
                }
             }
          }

          DeferredDeletablesManager ddm = new DeferredDeletablesManager();
          ddm.register(resource);
          TransactionManager.registerFinalizableAt(blockDepth, ddm);
          return true;
       }

       /**
        * Registers a specific deletable to this manager. While the collection is a set, the
        * deletable won't be deleted twice.
        *
        * @param     deletable
        *            A resource meant to be registered for deletion.
        *
        * @return    <code>true</code> if the register was successful or <code>false</code> if the
        *            deletable was already registered in this manager.
        */
       public boolean register(DeferredDeletable deletable)
       {
          return deletables.add(deletable);
       }

       /**
        * Does the effective delete of the registered resources when this manager is finished.
        */
       @Override
       public void finished()
       {
          for (DeferredDeletable deletable : deletables)
          {
             deletable.deferredDelete();
          }
       }

       /**
        * The method is a no-op due to the fact that the delete defer is made only when the
        * the manager is notified through the {@code finished} method.
        */
       @Override
       public void deleted()
       {
          // no-op
       }

       /**
        * The method is a no-op due to the fact that the delete defer is made only when the
        * the manager is notified through the {@code finished} method.
        */
       @Override
       public void iterate()
       {
          // no-op
       }

       /**
        * The method is a no-op due to the fact that the delete defer is made only when the
        * the manager is notified through the {@code finished} method.
        */
       @Override
       public void retry()
       {
          // no-op
       }
    }