SelfManager.java

/*
** Module   : SelfManager.java
** Abstract : A manager for the SELF system handle.
**
** Copyright (c) 2013-2017, Golden Code Development Corporation.
**
** -#- -I- --Date-- --------------------------------Description-----------------------------------
** 001 CA  20130121 Created initial version.
** 002 CA  20130223 Fixed initialization of context-local data.
*/
/*
** 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
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*/

package com.goldencode.p2j.util;

import java.util.*;
import com.goldencode.p2j.security.*;

/**
 * This class manages scoping of the SELF system handle. Before the event executes its trigger/
 * procedure/etc, the manager for that event must call {@link #pushSelf(handle)} to save the 
 * latest handle on top of the stack. After the event has finish, the manager for that event must
 * call {@link #popSelf()}. 
 */
public class SelfManager
{
   /** Context-local data variable. */
   private static ContextLocal<WorkArea> local = new ContextLocal<WorkArea>()
   {
      /**
       * Initializes the work area, the first time it is requested within a new context.
       *
       * @return   The newly instantiated work area.
       */
      protected synchronized WorkArea initialValue()
      {
         return new WorkArea();
      }   
   };
   
   /**
    * Get the latest self handle. If this is called outside of a event processing block, it will
    * return unknown.
    * 
    * @return   See above.
    */
   public static handle self()
   {
      WorkArea wa = local.get();
      if (wa.self.isEmpty())
      {
         return new handle();
      }
      
      return new handle(wa.self.peek());
   }
   
   /**
    * Discard the last SELF handle.
    * 
    * @return   The last SELF handle.
    */
   public static handle popSelf()
   {
      return new handle(local.get().self.pop());
   }
   
   /**
    * Push the given handle as the new SELF handle.
    * 
    * @param    h
    *           The new SELF handle reference.
    */
   public static void pushSelf(handle h)
   {
      local.get().self.push(h);
   }
   
   /**
    * Container of context-local data.
    */
   private static class WorkArea
   {
      /** Stack of SELF handles. */
      private Deque<handle> self = new ArrayDeque<handle>();
   }
}