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//
// ========================================================================
// Copyright (c) 1995-2021 Mort Bay Consulting Pty Ltd and others.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util;
import java.util.AbstractList;
import java.util.Collection;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Objects;
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.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* A BlockingQueue backed by a circular array capable or growing.
*
* This queue is uses a variant of the two lock queue algorithm to provide an efficient queue or list backed by a growable circular array.
*
*
* Unlike {@link java.util.concurrent.ArrayBlockingQueue}, this class is able to grow and provides a blocking put call.
*
*
* The queue has both a capacity (the size of the array currently allocated) and a max capacity (the maximum size that may be allocated), which defaults to
* {@link Integer#MAX_VALUE}.
*
*
* @param The element type
*/
public class BlockingArrayQueue extends AbstractList implements BlockingQueue
{
/**
* The head offset in the {@link #_indexes} array, displaced by 15 slots to avoid false sharing with the array length (stored before the first element of
* the array itself).
*/
private static final int HEAD_OFFSET = MemoryUtils.getIntegersPerCacheLine() - 1;
/**
* The tail offset in the {@link #_indexes} array, displaced by 16 slots from the head to avoid false sharing with it.
*/
private static final int TAIL_OFFSET = HEAD_OFFSET + MemoryUtils.getIntegersPerCacheLine();
/**
* Default initial capacity, 128.
*/
public static final int DEFAULT_CAPACITY = 128;
/**
* Default growth factor, 64.
*/
public static final int DEFAULT_GROWTH = 64;
private final int _maxCapacity;
private final int _growCapacity;
/**
* Array that holds the head and tail indexes, separated by a cache line to avoid false sharing
*/
private final int[] _indexes = new int[TAIL_OFFSET + 1];
private final Lock _tailLock = new ReentrantLock();
private final AtomicInteger _size = new AtomicInteger();
private final Lock _headLock = new ReentrantLock();
private final Condition _notEmpty = _headLock.newCondition();
private Object[] _elements;
/**
* Creates an unbounded {@link BlockingArrayQueue} with default initial capacity and grow factor.
*
* @see #DEFAULT_CAPACITY
* @see #DEFAULT_GROWTH
*/
public BlockingArrayQueue()
{
_elements = new Object[DEFAULT_CAPACITY];
_growCapacity = DEFAULT_GROWTH;
_maxCapacity = Integer.MAX_VALUE;
}
/**
* Creates a bounded {@link BlockingArrayQueue} that does not grow. The capacity of the queue is fixed and equal to the given parameter.
*
* @param maxCapacity the maximum capacity
*/
public BlockingArrayQueue(int maxCapacity)
{
_elements = new Object[maxCapacity];
_growCapacity = -1;
_maxCapacity = maxCapacity;
}
/**
* Creates an unbounded {@link BlockingArrayQueue} that grows by the given parameter.
*
* @param capacity the initial capacity
* @param growBy the growth factor
*/
public BlockingArrayQueue(int capacity, int growBy)
{
_elements = new Object[capacity];
_growCapacity = growBy;
_maxCapacity = Integer.MAX_VALUE;
}
/**
* Create a bounded {@link BlockingArrayQueue} that grows by the given parameter.
*
* @param capacity the initial capacity
* @param growBy the growth factor
* @param maxCapacity the maximum capacity
*/
public BlockingArrayQueue(int capacity, int growBy, int maxCapacity)
{
if (capacity > maxCapacity)
throw new IllegalArgumentException();
_elements = new Object[capacity];
_growCapacity = growBy;
_maxCapacity = maxCapacity;
}
/* Collection methods */
@Override
public void clear()
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
_indexes[HEAD_OFFSET] = 0;
_indexes[TAIL_OFFSET] = 0;
_size.set(0);
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@Override
public int size()
{
return _size.get();
}
@Override
public Iterator iterator()
{
return listIterator();
}
/* Queue methods */
@SuppressWarnings("unchecked")
@Override
public E poll()
{
if (_size.get() == 0)
return null;
E e = null;
_headLock.lock(); // Size cannot shrink
try
{
if (_size.get() > 0)
{
final int head = _indexes[HEAD_OFFSET];
e = (E)_elements[head];
_elements[head] = null;
_indexes[HEAD_OFFSET] = (head + 1) % _elements.length;
if (_size.decrementAndGet() > 0)
_notEmpty.signal();
}
}
finally
{
_headLock.unlock();
}
return e;
}
@SuppressWarnings("unchecked")
@Override
public E peek()
{
if (_size.get() == 0)
return null;
E e = null;
_headLock.lock(); // Size cannot shrink
try
{
if (_size.get() > 0)
e = (E)_elements[_indexes[HEAD_OFFSET]];
}
finally
{
_headLock.unlock();
}
return e;
}
@Override
public E remove()
{
E e = poll();
if (e == null)
throw new NoSuchElementException();
return e;
}
@Override
public E element()
{
E e = peek();
if (e == null)
throw new NoSuchElementException();
return e;
}
/* BlockingQueue methods */
@Override
public boolean offer(E e)
{
Objects.requireNonNull(e);
boolean notEmpty = false;
_tailLock.lock(); // Size cannot grow... only shrink
try
{
int size = _size.get();
if (size >= _maxCapacity)
return false;
// Should we expand array?
if (size == _elements.length)
{
_headLock.lock();
try
{
if (!grow())
return false;
}
finally
{
_headLock.unlock();
}
}
// Re-read head and tail after a possible grow
int tail = _indexes[TAIL_OFFSET];
_elements[tail] = e;
_indexes[TAIL_OFFSET] = (tail + 1) % _elements.length;
notEmpty = _size.getAndIncrement() == 0;
}
finally
{
_tailLock.unlock();
}
if (notEmpty)
{
_headLock.lock();
try
{
_notEmpty.signal();
}
finally
{
_headLock.unlock();
}
}
return true;
}
@Override
public boolean add(E e)
{
if (offer(e))
return true;
else
throw new IllegalStateException();
}
@Override
public void put(E o) throws InterruptedException
{
// The mechanism to await and signal when the queue is full is not implemented
throw new UnsupportedOperationException();
}
@Override
public boolean offer(E o, long timeout, TimeUnit unit) throws InterruptedException
{
// The mechanism to await and signal when the queue is full is not implemented
throw new UnsupportedOperationException();
}
@SuppressWarnings("unchecked")
@Override
public E take() throws InterruptedException
{
E e = null;
_headLock.lockInterruptibly(); // Size cannot shrink
try
{
try
{
while (_size.get() == 0)
{
_notEmpty.await();
}
}
catch (InterruptedException ex)
{
_notEmpty.signal();
throw ex;
}
final int head = _indexes[HEAD_OFFSET];
e = (E)_elements[head];
_elements[head] = null;
_indexes[HEAD_OFFSET] = (head + 1) % _elements.length;
if (_size.decrementAndGet() > 0)
_notEmpty.signal();
}
finally
{
_headLock.unlock();
}
return e;
}
@SuppressWarnings("unchecked")
@Override
public E poll(long time, TimeUnit unit) throws InterruptedException
{
long nanos = unit.toNanos(time);
E e = null;
_headLock.lockInterruptibly(); // Size cannot shrink
try
{
try
{
while (_size.get() == 0)
{
if (nanos <= 0)
return null;
nanos = _notEmpty.awaitNanos(nanos);
}
}
catch (InterruptedException x)
{
_notEmpty.signal();
throw x;
}
int head = _indexes[HEAD_OFFSET];
e = (E)_elements[head];
_elements[head] = null;
_indexes[HEAD_OFFSET] = (head + 1) % _elements.length;
if (_size.decrementAndGet() > 0)
_notEmpty.signal();
}
finally
{
_headLock.unlock();
}
return e;
}
@Override
public boolean remove(Object o)
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
if (isEmpty())
return false;
final int head = _indexes[HEAD_OFFSET];
final int tail = _indexes[TAIL_OFFSET];
final int capacity = _elements.length;
int i = head;
while (true)
{
if (Objects.equals(_elements[i], o))
{
remove(i >= head ? i - head : capacity - head + i);
return true;
}
++i;
if (i == capacity)
i = 0;
if (i == tail)
return false;
}
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@Override
public int remainingCapacity()
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
return getCapacity() - size();
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@Override
public int drainTo(Collection c)
{
return drainTo(c, Integer.MAX_VALUE);
}
@Override
public int drainTo(Collection c, int maxElements)
{
int elements = 0;
_tailLock.lock();
try
{
_headLock.lock();
try
{
final int head = _indexes[HEAD_OFFSET];
final int tail = _indexes[TAIL_OFFSET];
final int capacity = _elements.length;
int i = head;
while (i != tail && elements < maxElements)
{
elements++;
c.add((E)_elements[i]);
++i;
if (i == capacity)
i = 0;
}
if (i == tail)
{
_indexes[HEAD_OFFSET] = 0;
_indexes[TAIL_OFFSET] = 0;
_size.set(0);
}
else
{
_indexes[HEAD_OFFSET] = i;
_size.addAndGet(-elements);
}
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
return elements;
}
/* List methods */
@SuppressWarnings("unchecked")
@Override
public E get(int index)
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
if (index < 0 || index >= _size.get())
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
int i = _indexes[HEAD_OFFSET] + index;
int capacity = _elements.length;
if (i >= capacity)
i -= capacity;
return (E)_elements[i];
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@Override
public void add(int index, E e)
{
if (e == null)
throw new NullPointerException();
_tailLock.lock();
try
{
_headLock.lock();
try
{
final int size = _size.get();
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
if (index == size)
{
add(e);
}
else
{
if (_indexes[TAIL_OFFSET] == _indexes[HEAD_OFFSET])
if (!grow())
throw new IllegalStateException("full");
// Re-read head and tail after a possible grow
int i = _indexes[HEAD_OFFSET] + index;
int capacity = _elements.length;
if (i >= capacity)
i -= capacity;
_size.incrementAndGet();
int tail = _indexes[TAIL_OFFSET];
_indexes[TAIL_OFFSET] = tail = (tail + 1) % capacity;
if (i < tail)
{
System.arraycopy(_elements, i, _elements, i + 1, tail - i);
_elements[i] = e;
}
else
{
if (tail > 0)
{
System.arraycopy(_elements, 0, _elements, 1, tail);
_elements[0] = _elements[capacity - 1];
}
System.arraycopy(_elements, i, _elements, i + 1, capacity - i - 1);
_elements[i] = e;
}
}
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@SuppressWarnings("unchecked")
@Override
public E set(int index, E e)
{
Objects.requireNonNull(e);
_tailLock.lock();
try
{
_headLock.lock();
try
{
if (index < 0 || index >= _size.get())
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
int i = _indexes[HEAD_OFFSET] + index;
int capacity = _elements.length;
if (i >= capacity)
i -= capacity;
E old = (E)_elements[i];
_elements[i] = e;
return old;
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@SuppressWarnings("unchecked")
@Override
public E remove(int index)
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
if (index < 0 || index >= _size.get())
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
int i = _indexes[HEAD_OFFSET] + index;
int capacity = _elements.length;
if (i >= capacity)
i -= capacity;
E old = (E)_elements[i];
int tail = _indexes[TAIL_OFFSET];
if (i < tail)
{
System.arraycopy(_elements, i + 1, _elements, i, tail - i);
--_indexes[TAIL_OFFSET];
}
else
{
System.arraycopy(_elements, i + 1, _elements, i, capacity - i - 1);
_elements[capacity - 1] = _elements[0];
if (tail > 0)
{
System.arraycopy(_elements, 1, _elements, 0, tail);
--_indexes[TAIL_OFFSET];
}
else
{
_indexes[TAIL_OFFSET] = capacity - 1;
}
_elements[_indexes[TAIL_OFFSET]] = null;
}
_size.decrementAndGet();
return old;
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
@Override
public ListIterator listIterator(int index)
{
_tailLock.lock();
try
{
_headLock.lock();
try
{
Object[] elements = new Object[size()];
if (size() > 0)
{
int head = _indexes[HEAD_OFFSET];
int tail = _indexes[TAIL_OFFSET];
if (head < tail)
{
System.arraycopy(_elements, head, elements, 0, tail - head);
}
else
{
int chunk = _elements.length - head;
System.arraycopy(_elements, head, elements, 0, chunk);
System.arraycopy(_elements, 0, elements, chunk, tail);
}
}
return new Itr(elements, index);
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
/**
* @return the current capacity of this queue
*/
public int getCapacity()
{
_tailLock.lock();
try
{
return _elements.length;
}
finally
{
_tailLock.unlock();
}
}
/**
* @return the max capacity of this queue, or -1 if this queue is unbounded
*/
public int getMaxCapacity()
{
return _maxCapacity;
}
private boolean grow()
{
if (_growCapacity <= 0)
return false;
_tailLock.lock();
try
{
_headLock.lock();
try
{
final int head = _indexes[HEAD_OFFSET];
final int tail = _indexes[TAIL_OFFSET];
final int newTail;
final int capacity = _elements.length;
Object[] elements = new Object[capacity + _growCapacity];
if (head < tail)
{
newTail = tail - head;
System.arraycopy(_elements, head, elements, 0, newTail);
}
else if (head > tail || _size.get() > 0)
{
newTail = capacity + tail - head;
int cut = capacity - head;
System.arraycopy(_elements, head, elements, 0, cut);
System.arraycopy(_elements, 0, elements, cut, tail);
}
else
{
newTail = 0;
}
_elements = elements;
_indexes[HEAD_OFFSET] = 0;
_indexes[TAIL_OFFSET] = newTail;
return true;
}
finally
{
_headLock.unlock();
}
}
finally
{
_tailLock.unlock();
}
}
private class Itr implements ListIterator
{
private final Object[] _elements;
private int _cursor;
public Itr(Object[] elements, int offset)
{
_elements = elements;
_cursor = offset;
}
@Override
public boolean hasNext()
{
return _cursor < _elements.length;
}
@SuppressWarnings("unchecked")
@Override
public E next()
{
return (E)_elements[_cursor++];
}
@Override
public boolean hasPrevious()
{
return _cursor > 0;
}
@SuppressWarnings("unchecked")
@Override
public E previous()
{
return (E)_elements[--_cursor];
}
@Override
public int nextIndex()
{
return _cursor + 1;
}
@Override
public int previousIndex()
{
return _cursor - 1;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
@Override
public void set(E e)
{
throw new UnsupportedOperationException();
}
@Override
public void add(E e)
{
throw new UnsupportedOperationException();
}
}
}