/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.marmotta.platform.core.util;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
/**
* A blocking queue implementation backed by a linked hash set for predictable iteration order and
* constant time addition, removal and contains operations.
* <p/>
* Author: Sebastian Schaffert
*/
public class LinkedHashSetBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E> {
private int capacity = Integer.MAX_VALUE;
/** Current number of elements */
private final AtomicInteger count = new AtomicInteger(0);
/** Lock held by take, poll, etc */
private final ReentrantLock takeLock = new ReentrantLock();
/** Wait queue for waiting takes */
private final Condition notEmpty = takeLock.newCondition();
/** Lock held by put, offer, etc */
private final ReentrantLock putLock = new ReentrantLock();
/** Wait queue for waiting puts */
private final Condition notFull = putLock.newCondition();
private final LinkedHashSet<E> delegate;
public LinkedHashSetBlockingQueue() {
delegate = new LinkedHashSet<E>();
}
public LinkedHashSetBlockingQueue(int capacity) {
this.delegate = new LinkedHashSet<E>(capacity);
this.capacity = capacity;
}
@Override
public boolean offer(E e) {
if (e == null) throw new NullPointerException();
final AtomicInteger count = this.count;
if (count.get() == capacity)
return false;
int c = -1;
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
if (count.get() < capacity) {
final boolean wasAdded = enqueue(e);
c = wasAdded?count.getAndIncrement():count.get();
if (c + 1 < capacity)
notFull.signal();
}
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
return c >= 0;
}
@Override
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
while (count.get() == capacity) {
notFull.await();
}
final boolean wasAdded = enqueue(e);
c = wasAdded?count.getAndIncrement():count.get();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
}
@Override
public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException {
if (e == null) throw new NullPointerException();
long nanos = unit.toNanos(timeout);
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
while (count.get() == capacity) {
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
final boolean wasAdded = enqueue(e);
c = wasAdded?count.getAndIncrement():count.get();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
return true;
}
@Override
public E take() throws InterruptedException {
E x;
int c = -1;
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
while (count.get() == 0) {
notEmpty.await();
}
x = dequeue();
c = count.getAndDecrement();
if (c > 1)
notEmpty.signal();
} finally {
takeLock.unlock();
}
if (c == capacity)
signalNotFull();
return x;
}
@Override
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
E x = null;
int c = -1;
long nanos = unit.toNanos(timeout);
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
while (count.get() == 0) {
if (nanos <= 0)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
x = dequeue();
c = count.getAndDecrement();
if (c > 1)
notEmpty.signal();
} finally {
takeLock.unlock();
}
if (c == capacity)
signalNotFull();
return x;
}
@Override
public int remainingCapacity() {
return Integer.MAX_VALUE - size();
}
@Override
public int drainTo(Collection<? super E> c) {
return drainTo(c,Integer.MAX_VALUE);
}
@Override
public int drainTo(Collection<? super E> c, int maxElements) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
boolean signalNotFull = false;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
int n = Math.min(maxElements, count.get());
Iterator<E> it = delegate.iterator();
for(int i=0; i<n && it.hasNext(); i++) {
E x = it.next();
c.add(x);
}
count.getAndAdd(-n);
return n;
} finally {
takeLock.unlock();
if (signalNotFull)
signalNotFull();
}
}
@Override
public E poll() {
final AtomicInteger count = this.count;
if (count.get() == 0)
return null;
E x = null;
int c = -1;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
if (count.get() > 0) {
x = dequeue();
c = count.getAndDecrement();
if (c > 1)
notEmpty.signal();
}
} finally {
takeLock.unlock();
}
if (c == capacity)
signalNotFull();
return x;
}
@Override
public E peek() {
if (count.get() == 0)
return null;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
Iterator<E> it = delegate.iterator();
if(it.hasNext()) {
return it.next();
} else {
return null;
}
} finally {
takeLock.unlock();
}
}
/**
* Creates a node and links it at end of queue.
* @param x the item
* @return <code>true</code> if this set did not already contain <code>x</code>
*/
private boolean enqueue(E x) {
synchronized (delegate) {
return delegate.add(x);
}
}
/**
* Removes a node from head of queue.
* @return the node
*/
private E dequeue() {
synchronized (delegate) {
Iterator<E> it = delegate.iterator();
E x = it.next();
it.remove();
return x;
}
}
/**
* Lock to prevent both puts and takes.
*/
void fullyLock() {
putLock.lock();
takeLock.lock();
}
/**
* Unlock to allow both puts and takes.
*/
void fullyUnlock() {
takeLock.unlock();
putLock.unlock();
}
/**
* Signals a waiting take. Called only from put/offer (which do not
* otherwise ordinarily lock takeLock.)
*/
private void signalNotEmpty() {
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
notEmpty.signal();
} finally {
takeLock.unlock();
}
}
/**
* Signals a waiting put. Called only from take/poll.
*/
private void signalNotFull() {
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
notFull.signal();
} finally {
putLock.unlock();
}
}
/**
* Tells whether both locks are held by current thread.
*/
boolean isFullyLocked() {
return (putLock.isHeldByCurrentThread() &&
takeLock.isHeldByCurrentThread());
}
@Override
public Iterator<E> iterator() {
final Iterator<E> it = delegate.iterator();
return new Iterator<E>() {
@Override
public boolean hasNext() {
fullyLock();
try {
return it.hasNext();
} finally {
fullyUnlock();
}
}
@Override
public E next() {
fullyLock();
try {
return it.next();
} finally {
fullyUnlock();
}
}
@Override
public void remove() {
fullyLock();
try {
it.remove();
// remove counter
count.getAndDecrement();
} finally {
fullyUnlock();
}
}
};
}
@Override
public int size() {
return count.get();
}
@Override
public boolean remove(Object o) {
if (o == null) return false;
fullyLock();
try {
if(delegate.remove(o)) {
if(count.getAndDecrement() == capacity) {
notFull.signal();
}
return true;
}
} finally {
fullyUnlock();
}
return false;
}
@Override
public void clear() {
fullyLock();
try {
delegate.clear();
count.set(0);
} finally {
fullyUnlock();
}
}
}