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SnappyData store based off Pivotal GemFireXD
/** Notice of modification as required by the LGPL
* This file was modified by Gemstone Systems Inc. on
* $Date$
**/
// $Id: List.java,v 1.10 2005/04/12 12:59:21 belaban Exp $
package com.gemstone.org.jgroups.util;
import java.io.*;
import java.util.Enumeration;
import java.util.NoSuchElementException;
import java.util.Vector;
/**
* Doubly-linked list. Elements can be added at head or tail and removed from head/tail.
* This class is tuned for element access at either head or tail, random access to elements
* is not very fast; in this case use Vector. Concurrent access is supported: a thread is blocked
* while another thread adds/removes an object. When no objects are available, removal returns null.
* @author Bela Ban
*/
public class List implements Externalizable, Cloneable {
protected Element head=null, tail=null;
protected int size=0;
protected transient final Object mutex=new Object();
static/*GemStoneAddition*/ class Element {
Object obj=null;
Element next=null;
Element prev=null;
Element(Object o) {
obj=o;
}
}
public List() {
}
/**
Adds an object at the tail of the list.
*/
public void add(Object obj) {
Element el=new Element(obj);
synchronized(mutex) {
if(head == null) {
head=el;
tail=head;
size=1;
}
else {
el.prev=tail;
tail.next=el;
tail=el;
size++;
}
}
}
/**
Adds an object at the head of the list.
*/
public void addAtHead(Object obj) {
Element el=new Element(obj);
synchronized(mutex) {
if(head == null) {
head=el;
tail=head;
size=1;
}
else {
el.next=head;
head.prev=el;
head=el;
size++;
}
}
}
/**
Removes an object from the tail of the list. Returns null if no elements available
*/
public Object remove() {
Element retval=null;
synchronized(mutex) {
if(tail == null)
return null;
retval=tail;
if(head == tail) { // last element
head=null;
tail=null;
}
else {
tail.prev.next=null;
tail=tail.prev;
retval.prev=null;
}
size--;
}
return retval.obj;
}
/** Removes an object from the head of the list. Returns null if no elements available */
public Object removeFromHead() {
Element retval=null;
synchronized(mutex) {
if(head == null)
return null;
retval=head;
if(head == tail) { // last element
head=null;
tail=null;
}
else {
head=head.next;
head.prev=null;
retval.next=null;
}
size--;
}
return retval.obj;
}
/**
Returns element at the tail (if present), but does not remove it from list.
*/
public Object peek() {
synchronized(mutex) {
return tail != null ? tail.obj : null;
}
}
/**
Returns element at the head (if present), but does not remove it from list.
*/
public Object peekAtHead() {
synchronized(mutex) {
return head != null ? head.obj : null;
}
}
/**
Removes element obj from the list, checking for equality using the equals
operator. Only the first duplicate object is removed. Returns the removed object.
*/
public Object removeElement(Object obj) {
Element el=null;
Object retval=null;
synchronized(mutex) {
el=head;
while(el != null) {
if(el.obj.equals(obj)) {
retval=el.obj;
if(head == tail) { // only 1 element left in the list
head=null;
tail=null;
}
else
if(el.prev == null) { // we're at the head
head=el.next;
head.prev=null;
el.next=null;
}
else
if(el.next == null) { // we're at the tail
tail=el.prev;
tail.next=null;
el.prev=null;
}
else { // we're somewhere in the middle of the list
el.prev.next=el.next;
el.next.prev=el.prev;
el.next=null;
el.prev=null;
}
size--;
break;
}
el=el.next;
}
}
return retval;
}
public void removeAll() {
synchronized(mutex) {
size=0;
head=null;
tail=null;
}
}
public int size() {
return size;
}
@Override // GemStoneAddition
public String toString() {
StringBuffer ret=new StringBuffer("[");
Element el=head;
while(el != null) {
if(el.obj != null)
ret.append(el.obj + " ");
el=el.next;
}
ret.append(']');
return ret.toString();
}
public String dump() {
StringBuffer ret=new StringBuffer("[");
for(Element el=head; el != null; el=el.next)
ret.append(el.obj + " ");
return ret.toString() + ']';
}
public Vector getContents() {
Vector retval=new Vector(size);
Element el;
synchronized(mutex) {
el=head;
while(el != null) {
retval.addElement(el.obj);
el=el.next;
}
}
return retval;
}
public Enumeration elements() {
return new ListEnumerator(head);
}
public boolean contains(Object obj) {
Element el=head;
while(el != null) {
if(el.obj != null && el.obj.equals(obj))
return true;
el=el.next;
}
return false;
}
public List copy() {
List retval=new List();
synchronized(mutex) {
for(Element el=head; el != null; el=el.next)
retval.add(el.obj);
}
return retval;
}
@Override // GemStoneAddition
protected Object clone() throws CloneNotSupportedException {
// calling clone() is superfluous because we don't want a shallow copy
return copy();
}
public void writeExternal(ObjectOutput out) throws IOException {
Element el;
synchronized(mutex) {
el=head;
out.writeInt(size);
for(int i=0; i < size; i++) {
out.writeObject(el.obj);
el=el.next;
}
}
}
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
Object obj;
int new_size=in.readInt();
if(new_size == 0)
return;
for(int i=0; i < new_size; i++) {
obj=in.readObject();
add(obj);
}
}
// public void writeTo(DataOutputStream out) throws IOException {
// Element el;
// Object obj;
// if(size == 0) {
// out.writeInt(0);
// return;
// }
// out.writeInt(size);
// el=head;
// while(el != null) {
// obj=el.obj;
// if(obj instanceof Streamable) {
// out.writeByte(1);
// ((Streamable)obj).writeTo(out);
// }
// else {
// out.writeByte(0);
// ObjectOutputStream oos=new ObjectOutputStream(out); // very inefficient
// oos.writeObject(obj);
// oos.close();
// }
// el=el.next;
// }
// }
//
// public void readFrom(DataInputStream in) throws IOException, IllegalAccessException, InstantiationException {
// Object obj;
// int size=in.readInt();
// byte b;
//
// for(int i=0; i < size; i++) {
// b=in.readByte();
// if(b == 1) {
//
// }
// else if(b == 0) {
//
// }
// else
// throw new InstantiationException("byte '" + b + "' not recognized (needs to be 1 or 0)");
// }
//
// }
static/*GemStoneAddition*/ class ListEnumerator implements Enumeration {
Element curr=null;
ListEnumerator(Element start) {
curr=start;
}
public boolean hasMoreElements() {
return curr != null;
}
public Object nextElement() {
Object retval;
if(curr == null)
throw new NoSuchElementException();
retval=curr.obj;
curr=curr.next;
return retval;
}
}
// public static void main(String args[]) {
// List l=new List();
// l.add("Bela");
// l.add("Janet");
// l.add("Marco");
// l.add("Ralph");
// for(Enumeration e=l.elements(); e.hasMoreElements();) {
// System.out.println(e.nextElement());
// }
// System.out.println(l + ".contains(\"Bela\"): " + l.contains("Bela"));
// l.add(Integer.valueOf(1));
// l.add(Integer.valueOf(2));
// l.add(Integer.valueOf(5));
// l.add(Integer.valueOf(6));
// System.out.println(l + ".contains(2): " + l.contains(Integer.valueOf(2)));
// }
// public static void main(String[] args) {
// List l=new List();
// Long n;
//
//
// l.addAtHead(Integer.valueOf(1));
// l.addAtHead(Integer.valueOf(2));
// l.addAtHead(Integer.valueOf(3));
// l.addAtHead(Integer.valueOf(4));
// l.addAtHead(Integer.valueOf(5));
//
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
// System.out.println("Removed from head: " + l.removeFromHead());
//
//
// System.out.print("Adding 50000 numbers:");
// for(long i=0; i < 50000; i++) {
// n=Long.valueOf(i);
// if(i % 2 == 0) {
// l.addAtHead(n);
// }
// else {
// l.add(n);
// }
// }
// System.out.println(" OK");
//
// long num=0;
// System.out.print("Removing all elements: ");
// while((l.remove()) != null)
// num++;
// System.out.println("OK, removed " + num + " objects");
// }
}