/**

* 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.

**/

/* rich Jun 28, 2007 */

package clojure.lang;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

public class Delay implements IDeref, IPending{

Object val;

Throwable exception;

IFn fn;

volatile Lock lock;

public Delay(IFn f){

fn = f;

val = null;

exception = null;

lock = new ReentrantLock();

}

static public Object force(Object x) {

return (x instanceof Delay) ?

((Delay) x).deref()

: x;

}

private void realize() {

Lock l = lock;

if(l != null) {

l.lock();

try {

if(fn!=null) {

try {

val = fn.invoke();

} catch (Throwable t) {

exception = t;

}

fn = null;

lock = null;

}

} finally {

l.unlock();

}

}

}

public Object deref() {

if(lock != null)

realize();

if(exception != null)

throw Util.sneakyThrow(exception);

return val;

}

public boolean isRealized(){

return lock == null;

}

}