/*
* @(#)$Id: codetemplate_xbird.xml 943 2006-09-13 07:03:37Z yui $
*
* Copyright 2006-2008 Makoto YUI
*
* 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.
*
* Contributors:
* Makoto YUI - initial implementation
*/
package xbird.util.concurrent.collections;
import java.util.AbstractQueue;
import java.util.Iterator;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReferenceArray;
/**
*
* <DIV lang="en"></DIV>
* <DIV lang="ja"></DIV>
*
* @author Makoto YUI (yuin405+xbird@gmail.com)
*/
public final class ConcurrentBoundedQueue<E> extends AbstractQueue<E> implements Queue<E> {
private final int _capacity;
private final AtomicReferenceArray<E> _array;
private final AtomicInteger _readPtr, _writePtr;
private final AtomicInteger _used, _free; // as barriers
public ConcurrentBoundedQueue(int capacity) {
this._capacity = capacity;
this._array = new AtomicReferenceArray<E>(capacity);
this._readPtr = new AtomicInteger(0);
this._writePtr = new AtomicInteger(0);
this._used = new AtomicInteger(0);
this._free = new AtomicInteger(capacity);
}
public boolean offer(final E elem) {
if(elem == null) {
throw new NullPointerException();
}
for(;;) {
final int free = _free.get();
if(free == 0) {
return false; // no free space
}
if(_free.compareAndSet(free, free - 1)) {
break; // ensured that there are free space
}
}
int idx = _writePtr.get();
while(_array.compareAndSet(idx % _capacity, null, elem)) {
idx++;
}
_writePtr.getAndIncrement(); // intended.. always increment by one
_used.getAndIncrement();
return true;
}
public E poll() {
for(;;) {
final int used = _used.get();
if(used == 0) {
return null; // no entries
}
if(_used.compareAndSet(used, used - 1)) {
break; // ensured that there are entries
}
}
E elem;
for(int idx = _readPtr.get();; idx++) {
elem = _array.getAndSet(idx % _capacity, null);
if(elem != null) {
break;
}
// Since it is ensured that there are entries, it'll never be an infinity loop.
}
_readPtr.getAndIncrement(); // intended.. always increment by one
_free.getAndIncrement();
return elem;
}
public E peek() {
for(;;) {
final int used = _used.get();
if(used == 0) {
return null; // no entries
}
if(_used.compareAndSet(used, used - 1)) {
break; // ensured that there are entries
}
}
for(int idx = _readPtr.get();; idx++) {
final E elem = _array.get(idx % _capacity);
if(elem != null) {
return elem;
}
// Since it is ensured that there are entries, it'll never be an infinity loop.
}
}
@Override
public Iterator<E> iterator() {
throw new UnsupportedOperationException(); // TODO
}
@Override
public int size() {
return _used.get();
}
}