/*
* 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.
*/
/*
* This is a modified version of LinkedBlockingQueue.java The original was cvs revision 1.53 and was
* obtained for this url:
* http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/main/java/util/concurrent/
* LinkedBlockingQueue.java?view=log All modifications are marked with // GEMFIRE
*/
/*
* Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the
* public domain, as explained at http://creativecommons.org/licenses/publicdomain
*/
package org.apache.geode.internal.cache;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* The only difference between this class on LinkedBlockingQueue is the new method {@link #forcePut}
* which will always be added to the queue even if it exceeds the queue's capacity.
*
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on linked nodes. This queue
* orders elements FIFO (first-in-first-out). The <em>head</em> of the queue is that element that
* has been on the queue the longest time. The <em>tail</em> of the queue is that element that has
* been on the queue the shortest time. New elements are inserted at the tail of the queue, and the
* queue retrieval operations obtain elements at the head of the queue. Linked queues typically have
* higher throughput than array-based queues but less predictable performance in most concurrent
* applications.
*
* <p>
* The optional capacity bound constructor argument serves as a way to prevent excessive queue
* 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 queue above capacity.
*
* <p>
* This class and its iterator implement all of the <em>optional</em> methods of the
* {@link Collection} and {@link Iterator} interfaces.
*
* <p>
* This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @since GemFire 1.5
* @author Doug Lea
* @param <E> the type of elements held in this collection
*
*/
public class ForceableLinkedBlockingQueue<E> extends AbstractQueue<E>
implements BlockingQueue<E>, java.io.Serializable {
private static final long serialVersionUID = -6903933977591709194L;
/*
* A variant of the "two lock queue" algorithm. The putLock gates entry to put (and offer), and
* has an associated condition for waiting puts. Similarly for the takeLock. The "count" field
* that they both rely on is maintained as an atomic to avoid needing to get both locks in most
* cases. Also, to minimize need for puts to get takeLock and vice-versa, cascading notifies are
* used. When a put notices that it has enabled at least one take, it signals taker. That taker in
* turn signals others if more items have been entered since the signal. And symmetrically for
* takes signalling puts. Operations such as remove(Object) and iterators acquire both locks.
*
* Visibility between writers and readers is provided as follows:
*
* Whenever an element is enqueued, the putLock is acquired and count updated. A subsequent reader
* guarantees visibility to the enqueued Node by either acquiring the putLock (via fullyLock) or
* by acquiring the takeLock, and then reading n = count.get(); this gives visibility to the first
* n items.
*
* 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 advance to head.next.
*/
/**
* Linked list node class
*/
static class Node<E> {
E item;
/**
* One of: - the real successor Node - this Node, meaning the successor is head.next - null,
* meaning there is no successor (this is the last node)
*/
Node<E> next;
Node(E x) {
item = x;
}
}
/** The capacity bound, or Integer.MAX_VALUE if none */
private final int capacity;
/** Current number of elements */
private final AtomicInteger count = new AtomicInteger(0);
/**
* Head of linked list. Invariant: head.item == null
*/
private transient Node<E> head;
/**
* Tail of linked list. Invariant: last.next == null
*/
private transient Node<E> last;
/** 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();
/**
* 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();
}
}
/**
* Creates a node and links it at end of queue.
*
* @param x the item
*/
private void enqueue(E x) {
// assert putLock.isHeldByCurrentThread();
// assert last.next == null;
last = last.next = new Node<E>(x);
}
/**
* Removes a node from head of queue.
*
* @return the node
*/
private E dequeue() {
// assert takeLock.isHeldByCurrentThread();
// assert head.item == null;
Node<E> h = head;
Node<E> first = h.next;
h.next = h; // help GC
head = first;
E x = first.item;
first.item = null;
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();
}
// /**
// * Tells whether both locks are held by current thread.
// */
// boolean isFullyLocked() {
// return (putLock.isHeldByCurrentThread() &&
// takeLock.isHeldByCurrentThread());
// }
/**
* Creates a {@code ForceableLinkedBlockingQueue} with a capacity of {@link Integer#MAX_VALUE}.
*/
public ForceableLinkedBlockingQueue() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code ForceableLinkedBlockingQueue} with the given (fixed) capacity.
*
* @param capacity the capacity of this queue
* @throws IllegalArgumentException if {@code capacity} is not greater than zero
*/
public ForceableLinkedBlockingQueue(int capacity) {
if (capacity <= 0)
throw new IllegalArgumentException();
this.capacity = capacity;
last = head = new Node<E>(null);
}
// this doc comment is overridden to remove the reference to collections
// greater in size than Integer.MAX_VALUE
/**
* Returns the number of elements in this queue.
*
* @return the number of elements in this queue
*/
public int size() {
return count.get();
}
// this doc comment is a modified copy of the inherited doc comment,
// without the reference to unlimited queues.
/**
* Returns the number of additional elements that this queue can ideally (in the absence of memory
* or resource constraints) accept without blocking. This is always equal to the initial capacity
* of this queue less the current {@code size} of this queue.
*
* <p>
* Note that you <em>cannot</em> 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.
*/
public int remainingCapacity() {
return capacity - count.get();
}
/**
* Inserts the specified element at the tail of this queue, waiting if necessary for space to
* become available.
*
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public void put(E e) throws InterruptedException {
if (e == null)
throw new NullPointerException();
// Note: convention in all put/take/etc is to preset local var
// holding count negative to indicate failure unless set.
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
/*
* Note that count is used in wait guard even though it is not protected by lock. This works
* because count can only decrease at this point (all other puts are shut out by lock), and we
* (or some other waiting put) are signalled if it ever changes from capacity. Similarly for
* all other uses of count in other wait guards.
*/
while (count.get() >= capacity) { // GEMFIRE changed == to >=
notFull.await();
}
enqueue(e);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
}
/**
* Inserts the specified element at the tail of this queue even if the queue is currently at its
* capacity. // GEMFIRE addition
*/
public void forcePut(E e) throws InterruptedException {
if (e == null)
throw new NullPointerException();
// Note: convention in all put/take/etc is to preset local var
// holding count negative to indicate failure unless set.
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
enqueue(e);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
}
/**
* Inserts the specified element at the tail of this queue, waiting if necessary up to the
* specified wait time for space to become available.
*
* @return {@code true} if successful, or {@code false} if the specified waiting time elapses
* before space is available.
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
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) { // GEMFIRE changed == to >=
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
enqueue(e);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
return true;
}
/**
* Inserts the specified element at the tail of this queue if it is possible to do so immediately
* without exceeding the queue's capacity, returning {@code true} upon success and {@code false}
* if this queue is full. When using a capacity-restricted queue, this method is generally
* preferable to method {@link BlockingQueue#add add}, which can fail to insert an element only by
* throwing an exception.
*
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E e) {
if (e == null)
throw new NullPointerException();
final AtomicInteger count = this.count;
if (count.get() >= capacity) // GEMFIRE changed == to >=
return false;
int c = -1;
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
if (count.get() < capacity) {
enqueue(e);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal();
}
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
return c >= 0;
}
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;
}
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;
}
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;
}
public E peek() {
if (count.get() == 0)
return null;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
Node<E> first = head.next;
if (first == null)
return null;
else
return first.item;
} finally {
takeLock.unlock();
}
}
/**
* Unlinks interior Node p with predecessor trail.
*/
void unlink(Node<E> p, Node<E> trail) {
// assert isFullyLocked();
// p.next is not changed, to allow iterators that are
// traversing p to maintain their weak-consistency guarantee.
p.item = null;
trail.next = p.next;
if (last == p)
last = trail;
if (count.getAndDecrement() == capacity)
notFull.signal();
}
/**
* Removes a single instance of the specified element from this queue, if it is present. More
* formally, removes an element {@code e} such that {@code o.equals(e)}, if this queue contains
* one or more such elements. Returns {@code true} if this queue contained the specified element
* (or equivalently, if this queue changed as a result of the call).
*
* @param o element to be removed from this queue, if present
* @return {@code true} if this queue changed as a result of the call
*/
public boolean remove(Object o) {
if (o == null)
return false;
fullyLock();
try {
for (Node<E> trail = head, p = trail.next; p != null; trail = p, p = p.next) {
if (o.equals(p.item)) {
unlink(p, trail);
return true;
}
}
return false;
} finally {
fullyUnlock();
}
}
/**
* Returns an array containing all of the elements in this queue, in proper sequence.
*
* <p>
* The returned array will be "safe" in that no references to it are maintained by this queue. (In
* other words, this method must allocate a new array). The caller is thus free to modify the
* returned array.
*
* <p>
* This method acts as bridge between array-based and collection-based APIs.
*
* @return an array containing all of the elements in this queue
*/
public Object[] toArray() {
fullyLock();
try {
int size = count.get();
Object[] a = new Object[size];
int k = 0;
for (Node<E> p = head.next; p != null; p = p.next)
a[k++] = p.item;
return a;
} finally {
fullyUnlock();
}
}
/**
* Returns an array containing all of the elements in this queue, in proper sequence; the runtime
* type of the returned array is that of the specified array. If the queue fits in the specified
* array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the
* specified array and the size of this queue.
*
* <p>
* If this queue fits in the specified array with room to spare (i.e., the array has more elements
* than this queue), the element in the array immediately following the end of the queue is set to
* {@code null}.
*
* <p>
* Like the {@link #toArray()} method, this method acts as bridge between array-based and
* collection-based APIs. Further, this method allows precise control over the runtime type of the
* output array, and may, under certain circumstances, be used to save allocation costs.
*
* <p>
* Suppose {@code x} is a queue known to contain only strings. The following code can be used to
* dump the queue into a newly allocated array of {@code String}:
*
* <pre>
* String[] y = x.toArray(new String[0]);
* </pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to {@code toArray()}.
*
* @param a the array into which the elements of the queue are to be stored, if it is big enough;
* otherwise, a new array of the same runtime type is allocated for this purpose
* @return an array containing all of the elements in this queue
* @throws ArrayStoreException if the runtime type of the specified array is not a supertype of
* the runtime type of every element in this queue
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
fullyLock();
try {
int size = count.get();
if (a.length < size)
a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size);
int k = 0;
for (Node<E> p = head.next; p != null; p = p.next)
a[k++] = (T) p.item;
if (a.length > k)
a[k] = null;
return a;
} finally {
fullyUnlock();
}
}
public String toString() {
fullyLock();
try {
return super.toString();
} finally {
fullyUnlock();
}
}
/**
* Atomically removes all of the elements from this queue. The queue will be empty after this call
* returns.
*/
public void clear() {
fullyLock();
try {
for (Node<E> p, h = head; (p = h.next) != null; h = p) {
h.next = h;
p.item = null;
}
head = last;
// assert head.item == null && head.next == null;
if (count.getAndSet(0) >= capacity) // GEMFIRE changed == to >=
notFull.signal();
} finally {
fullyUnlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
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());
// count.get provides visibility to first n Nodes
Node<E> h = head;
int i = 0;
try {
while (i < n) {
Node<E> p = h.next;
c.add(p.item);
p.item = null;
h.next = h;
h = p;
++i;
}
return n;
} finally {
// Restore invariants even if c.add() threw
if (i > 0) {
// assert h.item == null;
head = h;
signalNotFull = (count.getAndAdd(-i) >= capacity); // GEMFIRE changed == to >=
}
}
} finally {
takeLock.unlock();
if (signalNotFull)
signalNotFull();
}
}
/**
* Returns an iterator over the elements in this queue in proper sequence. 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 queue in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
}
private class Itr implements Iterator<E> {
/*
* Basic weakly-consistent iterator. At all times hold the next item to hand out so that if
* hasNext() reports true, we will still have it to return even if lost race with a take etc.
*/
private Node<E> current;
private Node<E> lastRet;
private E currentElement;
Itr() {
fullyLock();
try {
current = head.next;
if (current != null)
currentElement = current.item;
} finally {
fullyUnlock();
}
}
public boolean hasNext() {
return current != null;
}
/**
* Returns the next live successor of p, or null if no such.
*
* Unlike other traversal methods, iterators need to handle both: - dequeued nodes (p.next == p)
* - (possibly multiple) interior removed nodes (p.item == null)
*/
private Node<E> nextNode(Node<E> p) {
for (;;) {
Node<E> s = p.next;
if (s == p)
return head.next;
if (s == null || s.item != null)
return s;
p = s;
}
}
public E next() {
fullyLock();
try {
if (current == null)
throw new NoSuchElementException();
E x = currentElement;
lastRet = current;
current = nextNode(current);
currentElement = (current == null) ? null : current.item;
return x;
} finally {
fullyUnlock();
}
}
public void remove() {
if (lastRet == null)
throw new IllegalStateException();
fullyLock();
try {
Node<E> node = lastRet;
lastRet = null;
for (Node<E> trail = head, p = trail.next; p != null; trail = p, p = p.next) {
if (p == node) {
unlink(p, trail);
break;
}
}
} finally {
fullyUnlock();
}
}
}
/**
* Save the state to a stream (that is, serialize it).
*
* @serialData The capacity is emitted (int), followed by all of its elements (each an
* {@code Object}) in the proper order, followed by a null
* @param s the stream
*/
private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
fullyLock();
try {
// Write out any hidden stuff, plus capacity
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node<E> p = head.next; p != null; p = p.next)
s.writeObject(p.item);
// Use trailing null as sentinel
s.writeObject(null);
} finally {
fullyUnlock();
}
}
/**
* Reconstitute this queue instance from a stream (that is, deserialize it).
*
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in capacity, and any hidden stuff
s.defaultReadObject();
count.set(0);
last = head = new Node<E>(null);
// Read in all elements and place in queue
for (;;) {
@SuppressWarnings("unchecked")
E item = (E) s.readObject();
if (item == null)
break;
add(item);
}
}
}