/*
* JBoss, Home of Professional Open Source
* Copyright 2010, Red Hat Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.as.ejb3.util;
import java.util.ArrayDeque;
import java.util.Deque;
/**
* A thread local stack data structure. In order to avoid memory churn the underlying
* ArrayDeque is never freed. If we remove the deque when it is empty then this results
* in excessive deque allocations.
*
* @author Stuart Douglas
*
*/
public class ThreadLocalStack<E> {
private static final Object NULL_VALUE = new Object();
private final ThreadLocal<Deque<Object>> deque = new ThreadLocal<Deque<Object>>() {
@Override
protected ArrayDeque<Object> initialValue() {
return new ArrayDeque<>();
}
};
public void push(E item) {
Deque<Object> st = deque.get();
if(item == null) {
st.push(NULL_VALUE);
} else {
st.push(item);
}
}
public E peek() {
Deque<Object> st = deque.get();
Object o = st.peek();
if(o == NULL_VALUE) {
return null;
} else {
return (E) o;
}
}
public E pop() {
Deque<Object> st = deque.get();
Object o = st.pop();
if(o == NULL_VALUE) {
return null;
} else {
return (E) o;
}
}
public boolean isEmpty() {
return deque.get().isEmpty();
}
}