ActiveMQ example source code file (DiskIndexLinkedList.java)

This example ActiveMQ source code file (DiskIndexLinkedList.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - ActiveMQ tags/keywords

diskindexlinkedlist, failed, failed, index, indexitem, indexitem, indexlinkedlist, indexoutofboundsexception, io, ioexception, ioexception, object, runtimeexception, storeentry, storeentry

The ActiveMQ DiskIndexLinkedList.java source code

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.activemq.kaha.impl.index;

import java.io.IOException;
import org.apache.activemq.kaha.StoreEntry;

/**
 * A linked list used by IndexItems
 * 
 * 
 */
public class DiskIndexLinkedList implements IndexLinkedList {
    protected IndexManager indexManager;
    protected transient IndexItem root;
    protected transient IndexItem last;
    protected transient int size;

    /**
     * Constructs an empty list.
     */
    public DiskIndexLinkedList(IndexManager im, IndexItem header) {
        this.indexManager = im;
        this.root = header;
    }

    public synchronized IndexItem getRoot() {
        return root;
    }

    public void setRoot(IndexItem e) {
        this.root = e;
    }

    /**
     * Returns the first element in this list.
     * 
     * @return the first element in this list.
     */
    public synchronized IndexItem getFirst() {
        if (size == 0) {
            return null;
        }
        return getNextEntry(root);
    }

    /**
     * Returns the last element in this list.
     * 
     * @return the last element in this list.
     */
    public synchronized IndexItem getLast() {
        if (size == 0) {
            return null;
        }
        if (last != null) {
            last.next = null;
            last.setNextItem(IndexItem.POSITION_NOT_SET);
        }
        return last;
    }

    /**
     * Removes and returns the first element from this list.
     * 
     * @return the first element from this list.
     */
    public synchronized StoreEntry removeFirst() {
        if (size == 0) {
            return null;
        }
        IndexItem result = getNextEntry(root);
        remove(result);
        return result;
    }

    /**
     * Removes and returns the last element from this list.
     * 
     * @return the last element from this list.
     */
    public synchronized Object removeLast() {
        if (size == 0) {
            return null;
        }
        StoreEntry result = last;
        remove(last);
        return result;
    }

    /**
     * Inserts the given element at the beginning of this list.
     * 
     * @param o the element to be inserted at the beginning of this list.
     */
    public synchronized void addFirst(IndexItem item) {
        if (size == 0) {
            last = item;
        }
        size++;
    }

    /**
     * Appends the given element to the end of this list. (Identical in function
     * to the <tt>add method; included only for consistency.)
     * 
     * @param o the element to be inserted at the end of this list.
     */
    public synchronized void addLast(IndexItem item) {
        size++;
        last = item;
    }

    /**
     * Returns the number of elements in this list.
     * 
     * @return the number of elements in this list.
     */
    public synchronized int size() {
        return size;
    }

    /**
     * is the list empty?
     * 
     * @return true if there are no elements in the list
     */
    public synchronized boolean isEmpty() {
        return size == 0;
    }

    /**
     * Appends the specified element to the end of this list.
     * 
     * @param o element to be appended to this list.
     * @return <tt>true (as per the general contract of
     *         <tt>Collection.add).
     */
    public synchronized boolean add(IndexItem item) {
        addLast(item);
        return true;
    }

    /**
     * Removes all of the elements from this list.
     */
    public synchronized void clear() {
        last = null;
        size = 0;
    }

    // Positional Access Operations
    /**
     * Returns the element at the specified position in this list.
     * 
     * @param index index of element to return.
     * @return the element at the specified position in this list.
     * @throws IndexOutOfBoundsException if the specified index is is out of
     *                 range (<tt>index < 0 || index >= size()).
     */
    public synchronized IndexItem get(int index) {
        return entry(index);
    }

    /**
     * Inserts the specified element at the specified position in this list.
     * Shifts the element currently at that position (if any) and any subsequent
     * elements to the right (adds one to their indices).
     * 
     * @param index index at which the specified element is to be inserted.
     * @param element element to be inserted.
     * @throws IndexOutOfBoundsException if the specified index is out of range (<tt>index < 0 || index > size()).
     */
    public synchronized void add(int index, IndexItem element) {
        if (index == size) {
            last = element;
        }
        size++;
    }

    /**
     * Removes the element at the specified position in this list. Shifts any
     * subsequent elements to the left (subtracts one from their indices).
     * Returns the element that was removed from the list.
     * 
     * @param index the index of the element to removed.
     * @return the element previously at the specified position.
     * @throws IndexOutOfBoundsException if the specified index is out of range (<tt>index < 0 || index >= size()).
     */
    public synchronized Object remove(int index) {
        IndexItem e = entry(index);
        remove(e);
        return e;
    }

    /**
     * Return the indexed entry.
     */
    private IndexItem entry(int index) {
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
        }
        IndexItem e = root;

        for (int i = 0; i <= index; i++) {
            e = getNextEntry(e);
        }
        if (e != null && last != null && last.equals(e)) {
            last = e;
        }
        return e;
    }

    // Search Operations
    /**
     * Returns the index in this list of the first occurrence of the specified
     * element, or -1 if the List does not contain this element. More formally,
     * returns the lowest index i such that
     * <tt>(o==null ? get(i)==null : o.equals(get(i))), or -1 if there
     * is no such index.
     * 
     * @param o element to search for.
     * @return the index in this list of the first occurrence of the specified
     *         element, or -1 if the list does not contain this element.
     */
    public synchronized int indexOf(StoreEntry o) {
        int index = 0;
        if (size > 0) {
            for (IndexItem e = getNextEntry(root); e != null; e = getNextEntry(e)) {
                if (o.equals(e)) {
                    return index;
                }
                index++;
            }
        }
        return -1;
    }

    /**
     * Retrieve the next entry after this entry
     * 
     * @param entry
     * @return next entry
     */
    public synchronized IndexItem getNextEntry(IndexItem current) {
		IndexItem result = null;
		if (current != null) {
			current = (IndexItem) refreshEntry(current);
			if (current.getNextItem() >= 0) {
				try {
					result = indexManager.getIndex(current.getNextItem());
				} catch (IOException e) {
					throw new RuntimeException("Failed to get next index from "
							+ indexManager + " for " + current, e);
				}
			}
		}
		// essential last get's updated consistently
		if (result != null && last != null && last.equals(result)) {
			last=result;
		}
		return result;
	}

    /**
	 * Retrive the prev entry after this entry
	 * 
	 * @param entry
	 * @return prev entry
	 */
    public synchronized IndexItem getPrevEntry(IndexItem current) {
		IndexItem result = null;
		if (current != null) {
			if (current.getPreviousItem() >= 0) {
				current = (IndexItem) refreshEntry(current);
				try {
					result = indexManager.getIndex(current.getPreviousItem());
				} catch (IOException e) {
					throw new RuntimeException(
							"Failed to  get current index for " + current, e);
				}
			}
		}
		// essential root get's updated consistently
		if (result != null && root != null && root.equals(result)) {
			return null;
		}
		return result;
	}

    public synchronized StoreEntry getEntry(StoreEntry current) {
        StoreEntry result = null;
        if (current != null && current.getOffset() >= 0) {
            try {
                result = indexManager.getIndex(current.getOffset());
            } catch (IOException e) {
                throw new RuntimeException("Failed to index", e);
            }
        }
        // essential root get's updated consistently
        if (result != null && root != null && root.equals(result)) {
            return root;
        }
        return result;
    }

    /**
     * Update the indexes of a StoreEntry
     * 
     * @param current
     */
    public synchronized StoreEntry refreshEntry(StoreEntry current) {
        StoreEntry result = null;
        if (current != null && current.getOffset() >= 0) {
            try {
                result = indexManager.refreshIndex((IndexItem)current);
            } catch (IOException e) {
                throw new RuntimeException("Failed to index", e);
            }
        }
        // essential root get's updated consistently
        if (result != null && root != null && root.equals(result)) {
            return root;
        }
        return result;
    }

    public synchronized void remove(IndexItem e) {
        if (e==null || e == root || e.equals(root)) {
            return;
        }
        if (e == last || e.equals(last)) {
            if (size > 1) {
                last = (IndexItem)refreshEntry(last);
                last = getPrevEntry(last);
            } else {
                last = null;
            }
        }
        size--;
    }
}