com.firefly.utils.collection.BlockingArrayQueue Maven / Gradle / Ivy
package com.firefly.utils.collection;
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;
import com.firefly.utils.concurrent.MemoryUtils;
/**
* 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 ie) {
_notEmpty.signal();
throw ie;
}
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) {
throw new UnsupportedOperationException();
}
@Override
public int drainTo(Collection c, int maxElements) {
throw new UnsupportedOperationException();
}
/*----------------------------------------------------------------------------*/
/* 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();
}
}
/*----------------------------------------------------------------------------*/
/* Additional methods */
/*----------------------------------------------------------------------------*/
/**
* @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;
}
/*----------------------------------------------------------------------------*/
/* Implementation methods */
/*----------------------------------------------------------------------------*/
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();
}
}
}