001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    package org.apache.directory.server.core.invocation;
021    
022    
023    import java.util.ArrayList;
024    import java.util.Collections;
025    import java.util.IdentityHashMap;
026    import java.util.List;
027    import java.util.Map;
028    
029    import org.apache.directory.server.core.interceptor.context.OperationContext;
030    
031    
032    /**
033     * Keeps track of recursive {@link Invocation}s.  This stack assumes an invocation
034     * occurs in the same thread since it is called first, so we manages stacks
035     * for each invocation in {@link ThreadLocal}-like manner.  You can just use
036     * {@link #getInstance()} to get current invocation stack.
037     * 
038     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
039     * @version $Rev: 896599 $, $Date: 2010-01-06 19:26:43 +0100 (Wed, 06 Jan 2010) $
040     */
041    public final class InvocationStack
042    {
043        // I didn't use ThreadLocal to release contexts explicitly.
044        // It seems like JDK 1.5 supports explicit release by introducing
045        // <tt>ThreadLocal.remove()</tt>, but we're still targetting 1.4.
046        private static final Map<Thread, InvocationStack> stacks = 
047            Collections.synchronizedMap( new IdentityHashMap<Thread, InvocationStack>() );
048    
049        private final Thread thread;
050        private final List<OperationContext> stack = new ArrayList<OperationContext>();
051    
052        
053        /**
054         * Returns the invocation stack of current thread.
055         */
056        public static InvocationStack getInstance()
057        {
058            Thread currentThread = Thread.currentThread();
059            InvocationStack ctx;
060            ctx = stacks.get( currentThread );
061    
062            if ( ctx == null )
063            {
064                ctx = new InvocationStack( currentThread );
065            }
066    
067            return ctx;
068        }
069        
070    
071        private InvocationStack( Thread currentThread )
072        {
073            thread = currentThread;
074            stacks.put( currentThread, this );
075        }
076    
077    
078        /**
079         * Returns an array of {@link Invocation}s.  0th element is the
080         * latest invocation.
081         */
082        public OperationContext[] toArray()
083        {
084            OperationContext[] result = new OperationContext[stack.size()];
085            result = stack.toArray( result );
086            return result;
087        }
088    
089    
090        /**
091         * Returns the latest invocation.
092         */
093        public OperationContext peek()
094        {
095            return stack.get( 0 );
096        }
097    
098    
099        /**
100         * Returns true if the stack is empty false otherwise.
101         */
102        public boolean isEmpty()
103        {
104            return stack.isEmpty();
105        }
106    
107    
108        /**
109         * Pushes the specified invocation to this stack.
110         */
111        public void push( OperationContext opContext )
112        {
113            stack.add( 0, opContext );
114        }
115    
116    
117        /**
118         * Pops the latest invocation from this stack.  This stack is released
119         * automatically if you pop all items from this stack.
120         */
121        public OperationContext pop()
122        {
123            OperationContext invocation = stack.remove( 0 );
124            
125            if ( stack.size() == 0 )
126            {
127                stacks.remove( thread );
128            }
129    
130            return invocation;
131        }
132    }