code: /**
   *   Copyright (c) Rich Hickey. All rights reserved.
   *   The use and distribution terms for this software are covered by the
   *   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
   *   which can be found in the file epl-v10.html at the root of this distribution.
   *   By using this software in any fashion, you are agreeing to be bound by
   * 	 the terms of this license.
   *   You must not remove this notice, or any other, from this software.
   **/
  
  package clojure.lang;
  
  import java.io.IOException;
  import java.io.NotSerializableException;
  import java.util.Iterator;
  
  public class IteratorSeq extends ASeq{
  
  private static final long serialVersionUID = -2631916503522522760L;
  
  final Iterator iter;
  final State state;
  
      static class State{
  	volatile Object val;
  	volatile Object _rest;
  }
  
  public static IteratorSeq create(Iterator iter){
  	if(iter.hasNext())
  		return new IteratorSeq(iter);
  	return null;
  }
  
  IteratorSeq(Iterator iter){
  	this.iter = iter;
  	state = new State();
  	this.state.val = state;
  	this.state._rest = state;
  }
  
  IteratorSeq(IPersistentMap meta, Iterator iter, State state){
  	super(meta);
  	this.iter = iter;
  	this.state = state;
  }
  
  public Object first(){
  	if(state.val == state)
  		synchronized(state)
  			{
  			if(state.val == state)
  				state.val = iter.next();
  			}
  	return state.val;
  }
  
  public ISeq next(){
  	if(state._rest == state)
  		synchronized(state)
  			{
  			if(state._rest == state)
  				{
  				first();
  				state._rest = create(iter);
  				}
  			}
  	return (ISeq) state._rest;
  }
  
  public IteratorSeq withMeta(IPersistentMap meta){
  	if(meta() == meta)
  		return this;
  	return new IteratorSeq(meta, iter, state);
  }
  
  private void writeObject (java.io.ObjectOutputStream out) throws IOException {
      throw new NotSerializableException(getClass().getName());
  }
  }
  