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/*
* 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.commons.pool2.impl;
import java.io.Serializable;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
/**
* An optionally-bounded {@linkplain java.util.concurrent.BlockingDeque blocking
* deque} based on linked nodes.
*
* The optional capacity bound constructor argument serves as a
* way to prevent excessive expansion. The capacity, if unspecified,
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
* dynamically created upon each insertion unless this would bring the
* deque above capacity.
*
*
Most operations run in constant time (ignoring time spent
* blocking). Exceptions include {@link #remove(Object) remove},
* {@link #removeFirstOccurrence removeFirstOccurrence}, {@link
* #removeLastOccurrence removeLastOccurrence}, {@link #contains
* contains}, {@link #iterator iterator.remove()}, and the bulk
* operations, all of which run in linear time.
*
*
This class and its iterator implement all of the
* optional methods of the {@link Collection} and {@link
* Iterator} interfaces.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @param the type of elements held in this collection
*
* Note: This was copied from Apache Harmony and modified to suit the needs of
* Commons Pool.
*
* @since 2.0
*/
class LinkedBlockingDeque extends AbstractQueue
implements Deque, Serializable {
/*
* Implemented as a simple doubly-linked list protected by a
* single lock and using conditions to manage blocking.
*
* To implement weakly consistent iterators, it appears we need to
* keep all Nodes GC-reachable from a predecessor dequeued Node.
* That would cause two problems:
* - allow a rogue Iterator to cause unbounded memory retention
* - cause cross-generational linking of old Nodes to new Nodes if
* a Node was tenured while live, which generational GCs have a
* hard time dealing with, causing repeated major collections.
* However, only non-deleted Nodes need to be reachable from
* dequeued Nodes, and reachability does not necessarily have to
* be of the kind understood by the GC. We use the trick of
* linking a Node that has just been dequeued to itself. Such a
* self-link implicitly means to jump to "first" (for next links)
* or "last" (for prev links).
*/
/*
* We have "diamond" multiple interface/abstract class inheritance
* here, and that introduces ambiguities. Often we want the
* BlockingDeque javadoc combined with the AbstractQueue
* implementation, so a lot of method specs are duplicated here.
*/
private static final long serialVersionUID = -387911632671998426L;
/**
* Doubly-linked list node class.
*
* @param node item type
*/
private static final class Node {
/**
* The item, or null if this node has been removed.
*/
E item;
/**
* One of:
* - the real predecessor Node
* - this Node, meaning the predecessor is tail
* - null, meaning there is no predecessor
*/
Node prev;
/**
* One of:
* - the real successor Node
* - this Node, meaning the successor is head
* - null, meaning there is no successor
*/
Node next;
/**
* Create a new list node.
*
* @param x The list item
* @param p Previous item
* @param n Next item
*/
Node(final E x, final Node p, final Node n) {
item = x;
prev = p;
next = n;
}
}
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
private transient Node first; // @GuardedBy("lock")
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
private transient Node last; // @GuardedBy("lock")
/** Number of items in the deque */
private transient int count; // @GuardedBy("lock")
/** Maximum number of items in the deque */
private final int capacity;
/** Main lock guarding all access */
private final InterruptibleReentrantLock lock;
/** Condition for waiting takes */
private final Condition notEmpty;
/** Condition for waiting puts */
private final Condition notFull;
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE}.
*/
public LinkedBlockingDeque() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE} and the given fairness policy.
* @param fairness true means threads waiting on the deque should be served
* as if waiting in a FIFO request queue
*/
public LinkedBlockingDeque(final boolean fairness) {
this(Integer.MAX_VALUE, fairness);
}
/**
* Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.
*
* @param capacity the capacity of this deque
* @throws IllegalArgumentException if {@code capacity} is less than 1
*/
public LinkedBlockingDeque(final int capacity) {
this(capacity, false);
}
/**
* Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity
* and fairness policy.
*
* @param capacity the capacity of this deque
* @param fairness true means threads waiting on the deque should be served
* as if waiting in a FIFO request queue
* @throws IllegalArgumentException if {@code capacity} is less than 1
*/
public LinkedBlockingDeque(final int capacity, final boolean fairness) {
if (capacity <= 0) {
throw new IllegalArgumentException();
}
this.capacity = capacity;
lock = new InterruptibleReentrantLock(fairness);
notEmpty = lock.newCondition();
notFull = lock.newCondition();
}
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE}, initially containing the elements of
* the given collection, added in traversal order of the
* collection's iterator.
*
* @param c the collection of elements to initially contain
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
public LinkedBlockingDeque(final Collection c) {
this(Integer.MAX_VALUE);
lock.lock(); // Never contended, but necessary for visibility
try {
for (final E e : c) {
if (e == null) {
throw new NullPointerException();
}
if (!linkLast(e)) {
throw new IllegalStateException("Deque full");
}
}
} finally {
lock.unlock();
}
}
// Basic linking and unlinking operations, called only while holding lock
/**
* Links provided element as first element, or returns false if full.
*
* @param e The element to link as the first element.
*
* @return {@code true} if successful, otherwise {@code false}
*/
private boolean linkFirst(final E e) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity) {
return false;
}
final Node f = first;
final Node x = new Node<>(e, null, f);
first = x;
if (last == null) {
last = x;
} else {
f.prev = x;
}
++count;
notEmpty.signal();
return true;
}
/**
* Links provided element as last element, or returns false if full.
*
* @param e The element to link as the last element.
*
* @return {@code true} if successful, otherwise {@code false}
*/
private boolean linkLast(final E e) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity) {
return false;
}
final Node l = last;
final Node x = new Node<>(e, l, null);
last = x;
if (first == null) {
first = x;
} else {
l.next = x;
}
++count;
notEmpty.signal();
return true;
}
/**
* Removes and returns the first element, or null if empty.
*
* @return The first element or {@code null} if empty
*/
private E unlinkFirst() {
// assert lock.isHeldByCurrentThread();
final Node f = first;
if (f == null) {
return null;
}
final Node n = f.next;
final E item = f.item;
f.item = null;
f.next = f; // help GC
first = n;
if (n == null) {
last = null;
} else {
n.prev = null;
}
--count;
notFull.signal();
return item;
}
/**
* Removes and returns the last element, or null if empty.
*
* @return The first element or {@code null} if empty
*/
private E unlinkLast() {
// assert lock.isHeldByCurrentThread();
final Node l = last;
if (l == null) {
return null;
}
final Node p = l.prev;
final E item = l.item;
l.item = null;
l.prev = l; // help GC
last = p;
if (p == null) {
first = null;
} else {
p.next = null;
}
--count;
notFull.signal();
return item;
}
/**
* Unlinks the provided node.
*
* @param x The node to unlink
*/
private void unlink(final Node x) {
// assert lock.isHeldByCurrentThread();
final Node p = x.prev;
final Node n = x.next;
if (p == null) {
unlinkFirst();
} else if (n == null) {
unlinkLast();
} else {
p.next = n;
n.prev = p;
x.item = null;
// Don't mess with x's links. They may still be in use by
// an iterator.
--count;
notFull.signal();
}
}
// BlockingDeque methods
/**
* {@inheritDoc}
*/
@Override
public void addFirst(final E e) {
if (!offerFirst(e)) {
throw new IllegalStateException("Deque full");
}
}
/**
* {@inheritDoc}
*/
@Override
public void addLast(final E e) {
if (!offerLast(e)) {
throw new IllegalStateException("Deque full");
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean offerFirst(final E e) {
if (e == null) {
throw new NullPointerException();
}
lock.lock();
try {
return linkFirst(e);
} finally {
lock.unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean offerLast(final E e) {
if (e == null) {
throw new NullPointerException();
}
lock.lock();
try {
return linkLast(e);
} finally {
lock.unlock();
}
}
/**
* Links the provided element as the first in the queue, waiting until there
* is space to do so if the queue is full.
*
* @param e element to link
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whilst waiting
* for space
*/
public void putFirst(final E e) throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
lock.lock();
try {
while (!linkFirst(e)) {
notFull.await();
}
} finally {
lock.unlock();
}
}
/**
* Links the provided element as the last in the queue, waiting until there
* is space to do so if the queue is full.
*
* @param e element to link
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whilst waiting
* for space
*/
public void putLast(final E e) throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
lock.lock();
try {
while (!linkLast(e)) {
notFull.await();
}
} finally {
lock.unlock();
}
}
/**
* Links the provided element as the first in the queue, waiting up to the
* specified time to do so if the queue is full.
*
* @param e element to link
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return {@code true} if successful, otherwise {@code false}
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whilst waiting
* for space
*/
public boolean offerFirst(final E e, final long timeout, final TimeUnit unit)
throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
try {
while (!linkFirst(e)) {
if (nanos <= 0) {
return false;
}
nanos = notFull.awaitNanos(nanos);
}
return true;
} finally {
lock.unlock();
}
}
/**
* Links the provided element as the last in the queue, waiting up to the
* specified time to do so if the queue is full.
*
* @param e element to link
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return {@code true} if successful, otherwise {@code false}
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whist waiting
* for space
*/
public boolean offerLast(final E e, final long timeout, final TimeUnit unit)
throws InterruptedException {
if (e == null) {
throw new NullPointerException();
}
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
try {
while (!linkLast(e)) {
if (nanos <= 0) {
return false;
}
nanos = notFull.awaitNanos(nanos);
}
return true;
} finally {
lock.unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public E removeFirst() {
final E x = pollFirst();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
/**
* {@inheritDoc}
*/
@Override
public E removeLast() {
final E x = pollLast();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
@Override
public E pollFirst() {
lock.lock();
try {
return unlinkFirst();
} finally {
lock.unlock();
}
}
@Override
public E pollLast() {
lock.lock();
try {
return unlinkLast();
} finally {
lock.unlock();
}
}
/**
* Unlinks the first element in the queue, waiting until there is an element
* to unlink if the queue is empty.
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E takeFirst() throws InterruptedException {
lock.lock();
try {
E x;
while ( (x = unlinkFirst()) == null) {
notEmpty.await();
}
return x;
} finally {
lock.unlock();
}
}
/**
* Unlinks the last element in the queue, waiting until there is an element
* to unlink if the queue is empty.
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E takeLast() throws InterruptedException {
lock.lock();
try {
E x;
while ( (x = unlinkLast()) == null) {
notEmpty.await();
}
return x;
} finally {
lock.unlock();
}
}
/**
* Unlinks the first element in the queue, waiting up to the specified time
* to do so if the queue is empty.
*
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E pollFirst(final long timeout, final TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
try {
E x;
while ( (x = unlinkFirst()) == null) {
if (nanos <= 0) {
return null;
}
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} finally {
lock.unlock();
}
}
/**
* Unlinks the last element in the queue, waiting up to the specified time
* to do so if the queue is empty.
*
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E pollLast(final long timeout, final TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
try {
E x;
while ( (x = unlinkLast()) == null) {
if (nanos <= 0) {
return null;
}
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} finally {
lock.unlock();
}
}
/**
* {@inheritDoc}
*/
@Override
public E getFirst() {
final E x = peekFirst();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
/**
* {@inheritDoc}
*/
@Override
public E getLast() {
final E x = peekLast();
if (x == null) {
throw new NoSuchElementException();
}
return x;
}
@Override
public E peekFirst() {
lock.lock();
try {
return first == null ? null : first.item;
} finally {
lock.unlock();
}
}
@Override
public E peekLast() {
lock.lock();
try {
return last == null ? null : last.item;
} finally {
lock.unlock();
}
}
@Override
public boolean removeFirstOccurrence(final Object o) {
if (o == null) {
return false;
}
lock.lock();
try {
for (Node p = first; p != null; p = p.next) {
if (o.equals(p.item)) {
unlink(p);
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
@Override
public boolean removeLastOccurrence(final Object o) {
if (o == null) {
return false;
}
lock.lock();
try {
for (Node p = last; p != null; p = p.prev) {
if (o.equals(p.item)) {
unlink(p);
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
// BlockingQueue methods
/**
* {@inheritDoc}
*/
@Override
public boolean add(final E e) {
addLast(e);
return true;
}
/**
* {@inheritDoc}
*/
@Override
public boolean offer(final E e) {
return offerLast(e);
}
/**
* Links the provided element as the last in the queue, waiting until there
* is space to do so if the queue is full.
*
* This method is equivalent to {@link #putLast(Object)}.
*
* @param e element to link
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whilst waiting
* for space
*/
public void put(final E e) throws InterruptedException {
putLast(e);
}
/**
* Links the provided element as the last in the queue, waiting up to the
* specified time to do so if the queue is full.
*
* This method is equivalent to {@link #offerLast(Object, long, TimeUnit)}
*
* @param e element to link
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return {@code true} if successful, otherwise {@code false}
*
* @throws NullPointerException if e is null
* @throws InterruptedException if the thread is interrupted whilst waiting
* for space
*/
public boolean offer(final E e, final long timeout, final TimeUnit unit)
throws InterruptedException {
return offerLast(e, timeout, unit);
}
/**
* Retrieves and removes the head of the queue represented by this deque.
* This method differs from {@link #poll poll} only in that it throws an
* exception if this deque is empty.
*
*
This method is equivalent to {@link #removeFirst() removeFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException if this deque is empty
*/
@Override
public E remove() {
return removeFirst();
}
@Override
public E poll() {
return pollFirst();
}
/**
* Unlinks the first element in the queue, waiting until there is an element
* to unlink if the queue is empty.
*
*
This method is equivalent to {@link #takeFirst()}.
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E take() throws InterruptedException {
return takeFirst();
}
/**
* Unlinks the first element in the queue, waiting up to the specified time
* to do so if the queue is empty.
*
*
This method is equivalent to {@link #pollFirst(long, TimeUnit)}.
*
* @param timeout length of time to wait
* @param unit units that timeout is expressed in
*
* @return the unlinked element
* @throws InterruptedException if the current thread is interrupted
*/
public E poll(final long timeout, final TimeUnit unit) throws InterruptedException {
return pollFirst(timeout, unit);
}
/**
* Retrieves, but does not remove, the head of the queue represented by
* this deque. This method differs from {@link #peek peek} only in that
* it throws an exception if this deque is empty.
*
*
This method is equivalent to {@link #getFirst() getFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException if this deque is empty
*/
@Override
public E element() {
return getFirst();
}
@Override
public E peek() {
return peekFirst();
}
/**
* Returns the number of additional elements that this deque can ideally
* (in the absence of memory or resource constraints) accept without
* blocking. This is always equal to the initial capacity of this deque
* less the current {@code size} of this deque.
*
*
Note that you cannot always tell if an attempt to insert
* an element will succeed by inspecting {@code remainingCapacity}
* because it may be the case that another thread is about to
* insert or remove an element.
*
* @return The number of additional elements the queue is able to accept
*/
public int remainingCapacity() {
lock.lock();
try {
return capacity - count;
} finally {
lock.unlock();
}
}
/**
* Drains the queue to the specified collection.
*
* @param c The collection to add the elements to
*
* @return number of elements added to the collection
*
* @throws UnsupportedOperationException if the add operation is not
* supported by the specified collection
* @throws ClassCastException if the class of the elements held by this
* collection prevents them from being added to the specified
* collection
* @throws NullPointerException if c is null
* @throws IllegalArgumentException if c is this instance
*/
public int drainTo(final Collection c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* Drains no more than the specified number of elements from the queue to the
* specified collection.
*
* @param c collection to add the elements to
* @param maxElements maximum number of elements to remove from the queue
*
* @return number of elements added to the collection
* @throws UnsupportedOperationException if the add operation is not
* supported by the specified collection
* @throws ClassCastException if the class of the elements held by this
* collection prevents them from being added to the specified
* collection
* @throws NullPointerException if c is null
* @throws IllegalArgumentException if c is this instance
*/
public int drainTo(final Collection c, final int maxElements) {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
lock.lock();
try {
final int n = Math.min(maxElements, count);
for (int i = 0; i < n; i++) {
c.add(first.item); // In this order, in case add() throws.
unlinkFirst();
}
return n;
} finally {
lock.unlock();
}
}
// Stack methods
/**
* {@inheritDoc}
*/
@Override
public void push(final E e) {
addFirst(e);
}
/**
* {@inheritDoc}
*/
@Override
public E pop() {
return removeFirst();
}
// Collection methods
/**
* Removes the first occurrence of the specified element from this deque.
* If the deque does not contain the element, it is unchanged.
* More formally, removes the first element {@code e} such that
* {@code o.equals(e)} (if such an element exists).
* Returns {@code true} if this deque contained the specified element
* (or equivalently, if this deque changed as a result of the call).
*
*
This method is equivalent to
* {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
*
* @param o element to be removed from this deque, if present
* @return {@code true} if this deque changed as a result of the call
*/
@Override
public boolean remove(final Object o) {
return removeFirstOccurrence(o);
}
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
@Override
public int size() {
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
/**
* Returns {@code true} if this deque contains the specified element.
* More formally, returns {@code true} if and only if this deque contains
* at least one element {@code e} such that {@code o.equals(e)}.
*
* @param o object to be checked for containment in this deque
* @return {@code true} if this deque contains the specified element
*/
@Override
public boolean contains(final Object o) {
if (o == null) {
return false;
}
lock.lock();
try {
for (Node p = first; p != null; p = p.next) {
if (o.equals(p.item)) {
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
/*
* TODO: Add support for more efficient bulk operations.
*
* We don't want to acquire the lock for every iteration, but we
* also want other threads a chance to interact with the
* collection, especially when count is close to capacity.
*/
// /**
// * Adds all of the elements in the specified collection to this
// * queue. Attempts to addAll of a queue to itself result in
// * {@code IllegalArgumentException}. Further, the behavior of
// * this operation is undefined if the specified collection is
// * modified while the operation is in progress.
// *
// * @param c collection containing elements to be added to this queue
// * @return {@code true} if this queue changed as a result of the call
// * @throws ClassCastException
// * @throws NullPointerException
// * @throws IllegalArgumentException
// * @throws IllegalStateException
// * @see #add(Object)
// */
// public boolean addAll(Collection c) {
// if (c == null)
// throw new NullPointerException();
// if (c == this)
// throw new IllegalArgumentException();
// final ReentrantLock lock = this.lock;
// lock.lock();
// try {
// boolean modified = false;
// for (E e : c)
// if (linkLast(e))
// modified = true;
// return modified;
// } finally {
// lock.unlock();
// }
// }
/**
* Returns an array containing all of the elements in this deque, in
* proper sequence (from first to last element).
*
* The returned array will be "safe" in that no references to it are
* maintained by this deque. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
*
This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this deque
*/
@Override
public Object[] toArray() {
lock.lock();
try {
final Object[] a = new Object[count];
int k = 0;
for (Node p = first; p != null; p = p.next) {
a[k++] = p.item;
}
return a;
} finally {
lock.unlock();
}
}
/**
* {@inheritDoc}
*/
@SuppressWarnings("unchecked")
@Override
public T[] toArray(T[] a) {
lock.lock();
try {
if (a.length < count) {
a = (T[])java.lang.reflect.Array.newInstance
(a.getClass().getComponentType(), count);
}
int k = 0;
for (Node p = first; p != null; p = p.next) {
a[k++] = (T)p.item;
}
if (a.length > k) {
a[k] = null;
}
return a;
} finally {
lock.unlock();
}
}
@Override
public String toString() {
lock.lock();
try {
return super.toString();
} finally {
lock.unlock();
}
}
/**
* Atomically removes all of the elements from this deque.
* The deque will be empty after this call returns.
*/
@Override
public void clear() {
lock.lock();
try {
for (Node f = first; f != null; ) {
f.item = null;
final Node n = f.next;
f.prev = null;
f.next = null;
f = n;
}
first = last = null;
count = 0;
notFull.signalAll();
} finally {
lock.unlock();
}
}
/**
* Returns an iterator over the elements in this deque in proper sequence.
* The elements will be returned in order from first (head) to last (tail).
* The returned {@code Iterator} is a "weakly consistent" iterator that
* will never throw {@link java.util.ConcurrentModificationException
* ConcurrentModificationException},
* and guarantees to traverse elements as they existed upon
* construction of the iterator, and may (but is not guaranteed to)
* reflect any modifications subsequent to construction.
*
* @return an iterator over the elements in this deque in proper sequence
*/
@Override
public Iterator iterator() {
return new Itr();
}
/**
* {@inheritDoc}
*/
@Override
public Iterator descendingIterator() {
return new DescendingItr();
}
/**
* Base class for Iterators for LinkedBlockingDeque
*/
private abstract class AbstractItr implements Iterator {
/**
* The next node to return in next()
*/
Node next;
/**
* nextItem holds on to item fields because once we claim that
* an element exists in hasNext(), we must return item read
* under lock (in advance()) even if it was in the process of
* being removed when hasNext() was called.
*/
E nextItem;
/**
* Node returned by most recent call to next. Needed by remove.
* Reset to null if this element is deleted by a call to remove.
*/
private Node lastRet;
/**
* Obtain the first node to be returned by the iterator.
*
* @return first node
*/
abstract Node firstNode();
/**
* For a given node, obtain the next node to be returned by the
* iterator.
*
* @param n given node
*
* @return next node
*/
abstract Node nextNode(Node n);
/**
* Create a new iterator. Sets the initial position.
*/
AbstractItr() {
// set to initial position
lock.lock();
try {
next = firstNode();
nextItem = next == null ? null : next.item;
} finally {
lock.unlock();
}
}
/**
* Returns the successor node of the given non-null, but
* possibly previously deleted, node.
*
* @param n node whose successor is sought
* @return successor node
*/
private Node succ(Node n) {
// Chains of deleted nodes ending in null or self-links
// are possible if multiple interior nodes are removed.
for (;;) {
final Node s = nextNode(n);
if (s == null) {
return null;
} else if (s.item != null) {
return s;
} else if (s == n) {
return firstNode();
} else {
n = s;
}
}
}
/**
* Advances next.
*/
void advance() {
lock.lock();
try {
// assert next != null;
next = succ(next);
nextItem = next == null ? null : next.item;
} finally {
lock.unlock();
}
}
@Override
public boolean hasNext() {
return next != null;
}
@Override
public E next() {
if (next == null) {
throw new NoSuchElementException();
}
lastRet = next;
final E x = nextItem;
advance();
return x;
}
@Override
public void remove() {
final Node n = lastRet;
if (n == null) {
throw new IllegalStateException();
}
lastRet = null;
lock.lock();
try {
if (n.item != null) {
unlink(n);
}
} finally {
lock.unlock();
}
}
}
/** Forward iterator */
private class Itr extends AbstractItr {
@Override
Node firstNode() { return first; }
@Override
Node nextNode(final Node n) { return n.next; }
}
/** Descending iterator */
private class DescendingItr extends AbstractItr {
@Override
Node firstNode() { return last; }
@Override
Node nextNode(final Node n) { return n.prev; }
}
/**
* Saves the state of this deque to a stream (that is, serialize it).
*
* @serialData The capacity (int), followed by elements (each an
* {@code Object}) in the proper order, followed by a null
* @param s the stream
*/
private void writeObject(final java.io.ObjectOutputStream s)
throws java.io.IOException {
lock.lock();
try {
// Write out capacity and any hidden stuff
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node p = first; p != null; p = p.next) {
s.writeObject(p.item);
}
// Use trailing null as sentinel
s.writeObject(null);
} finally {
lock.unlock();
}
}
/**
* Reconstitutes this deque from a stream (that is,
* deserialize it).
* @param s the stream
*/
private void readObject(final java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
count = 0;
first = null;
last = null;
// Read in all elements and place in queue
for (;;) {
@SuppressWarnings("unchecked")
final
E item = (E)s.readObject();
if (item == null) {
break;
}
add(item);
}
}
// Monitoring methods
/**
* Returns true if there are threads waiting to take instances from this deque. See disclaimer on accuracy in
* {@link java.util.concurrent.locks.ReentrantLock#hasWaiters(Condition)}.
*
* @return true if there is at least one thread waiting on this deque's notEmpty condition.
*/
public boolean hasTakeWaiters() {
lock.lock();
try {
return lock.hasWaiters(notEmpty);
} finally {
lock.unlock();
}
}
/**
* Returns the length of the queue of threads waiting to take instances from this deque. See disclaimer on accuracy
* in {@link java.util.concurrent.locks.ReentrantLock#getWaitQueueLength(Condition)}.
*
* @return number of threads waiting on this deque's notEmpty condition.
*/
public int getTakeQueueLength() {
lock.lock();
try {
return lock.getWaitQueueLength(notEmpty);
} finally {
lock.unlock();
}
}
/**
* Interrupts the threads currently waiting to take an object from the pool. See disclaimer on accuracy in
* {@link java.util.concurrent.locks.ReentrantLock#getWaitingThreads(Condition)}.
*/
public void interuptTakeWaiters() {
lock.lock();
try {
lock.interruptWaiters(notEmpty);
} finally {
lock.unlock();
}
}
}