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/*
* Copyright (c) 2001-2017, Zoltan Farkas All Rights Reserved.
*
* This library 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 library 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 General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Additionally licensed with:
*
* Licensed 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.spf4j.concurrent;
import java.util.concurrent.atomic.AtomicReference;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
/**
* A Treiber stack.
* @author Zoltan Farkas
* @param
*/
@ThreadSafe
public final class ConcurrentStack {
private final AtomicReference> top = new AtomicReference>();
public void push(@Nonnull final E item) {
Node oldHead;
Node newHead;
do {
oldHead = top.get();
newHead = new Node(item, oldHead);
} while (!top.compareAndSet(oldHead, newHead));
}
@Nullable
public E pop() {
Node oldHead;
Node newHead;
do {
oldHead = top.get();
if (oldHead == null) {
return null;
}
newHead = oldHead.next;
} while (!top.compareAndSet(oldHead, newHead));
return oldHead.item;
}
private static class Node {
private final E item;
private final Node next;
Node(final E item, @Nullable final Node next) {
this.item = item;
this.next = next;
}
}
@Override
public String toString() {
return "ConcurrentStack{" + "top=" + top + '}';
}
}
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