org.pvalsecc.concurrent.FArrayBlockingQueue Maven / Gradle / Ivy
/*
* Copyright (C) 2008 Patrick Valsecchi
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 U
*/
package org.pvalsecc.concurrent;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
/**
* Very much similar to the JDK ArrayBlockingQueue class.
*
* When the producer threads are blocked due to a queue full event,
* then the consumer threads will not signal the producers until a
* lower mark is reached again. The point is to give maximum CPU
* resources to the consumer threads for a while.
*/
@SuppressWarnings({"CallToSignalInsteadOfSignalAll", "LockAcquiredButNotSafelyReleased", "ObjectEquality", "AssignmentToMethodParameter"})
public final class FArrayBlockingQueue extends AbstractQueue implements BlockingQueue {
/**
* The queued items
*/
private final E[] items;
/**
* items index for next take, poll or remove
*/
private int takeIndex;
/**
* items index for next put, offer, or add.
*/
private int putIndex;
/**
* Number of items in the queue
*/
private int count;
/**
* See JAVAdoc of this class
*/
private int lowMark;
/**
* @see #lowMark
*/
private boolean movingBackToLowMark;
/*
* Concurrency control uses the classic two-condition algorithm
* found in any textbook.
*/
/**
* Main lock guarding all access
*/
private final ReentrantLock lock;
/**
* Condition for waiting takes
*/
private final Condition notEmpty;
/**
* Condition for waiting puts
*/
private final Condition notFull;
/**
* Circularly increment i.
*/
private int inc(int i) {
return (++i == items.length) ? 0 : i;
}
/**
* Insert element at current put position, advance, and signal.
* Call only when holding lock.
*/
private void insert(E x) {
items[putIndex] = x;
putIndex = inc(putIndex);
++count;
if (count == items.length) {
movingBackToLowMark = true;
}
notEmpty.signal();
}
/**
* Extract element at current take position, advance, and signal.
* Call only when holding lock.
*/
private E extract() {
final E[] items = this.items;
E x = items[takeIndex];
items[takeIndex] = null;
takeIndex = inc(takeIndex);
--count;
wakeupProducersIfNeeded();
return x;
}
/**
* Call only when holding lock.
*/
private void wakeupProducersIfNeeded() {
if (!movingBackToLowMark) // regular mode
{
notFull.signalAll();
} else // producers are waiting
{
if (count <= lowMark) {
movingBackToLowMark = false;
notFull.signalAll();
}
}
}
/**
* Utility for remove and iterator.remove: Delete item at position i.
* Call only when holding lock.
*/
void removeAt(int i) {
final E[] items = this.items;
// if removing front item, just advance
if (i == takeIndex) {
items[takeIndex] = null;
takeIndex = inc(takeIndex);
} else {
// slide over all others up through putIndex.
for (; ;) {
int nexti = inc(i);
if (nexti != putIndex) {
items[i] = items[nexti];
i = nexti;
} else {
items[i] = null;
putIndex = i;
break;
}
}
}
--count;
notFull.signal();
}
/**
* Creates an ArrayBlockingQueue with the given (fixed)
* capacity and default access policy.
*
* @param capacity the capacity of this queue
* @throws IllegalArgumentException if capacity is less than 1
*/
public FArrayBlockingQueue(int capacity) {
this(capacity, false);
}
/**
* Creates an ArrayBlockingQueue with the given (fixed)
* capacity and the specified access policy.
*
* @param capacity the capacity of this queue
* @param fair if true then queue accesses for threads blocked
* on insertion or removal, are processed in FIFO order; if false
* the access order is unspecified.
* @throws IllegalArgumentException if capacity is less than 1
*/
private FArrayBlockingQueue(int capacity, boolean fair) {
if (capacity <= 0) {
throw new IllegalArgumentException();
}
this.items = (E[]) new Object[capacity];
lock = new ReentrantLock(fair);
notEmpty = lock.newCondition();
notFull = lock.newCondition();
// This is still experimental: for the time being 1/3 is hardcoded.
{
//lowMark = capacity - (capacity / 3);
lowMark = capacity / 3;
}
}
/**
* Inserts the specified element at the tail of this queue if possible,
* returning immediately if this queue is full.
*
* @param o the element to add.
* @return true if it was possible to add the element to
* this queue, else false
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E o) {
if (o == null) {
throw new NullPointerException();
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == items.length) {
return false;
} else {
insert(o);
return true;
}
}
finally {
lock.unlock();
}
}
/**
* Inserts the specified element at the tail of this queue, waiting if
* necessary up to the specified wait time for space to become available.
*
* @param o the element to add
* @param timeout how long to wait before giving up, in units of
* unit
* @param unit a TimeUnit determining how to interpret the
* timeout parameter
* @return true if successful, or false if
* the specified waiting time elapses before space is available.
* @throws InterruptedException if interrupted while waiting.
* @throws NullPointerException if the specified element is null.
*/
public boolean offer(E o, long timeout, TimeUnit unit)
throws InterruptedException {
if (o == null) {
throw new NullPointerException();
}
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
long nanos = unit.toNanos(timeout);
for (; ;) {
if (count != items.length) {
insert(o);
return true;
}
if (nanos <= 0) {
return false;
}
try {
nanos = notFull.awaitNanos(nanos);
}
catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
}
}
finally {
lock.unlock();
}
}
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == 0) {
return null;
}
return extract();
}
finally {
lock.unlock();
}
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
long nanos = unit.toNanos(timeout);
for (; ;) {
if (count != 0) {
return extract();
}
if (nanos <= 0) {
return null;
}
try {
nanos = notEmpty.awaitNanos(nanos);
}
catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
}
}
finally {
lock.unlock();
}
}
/**
* Removes a single instance of the specified element from this
* queue, if it is present.
*/
public boolean remove(Object o) {
if (o == null) {
return false;
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
for (; ;) {
if (k++ >= count) {
return false;
}
if (o.equals(items[i])) {
removeAt(i);
return true;
}
i = inc(i);
}
}
finally {
lock.unlock();
}
}
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (count == 0) ? null : items[takeIndex];
}
finally {
lock.unlock();
}
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
while (count == 0) {
notEmpty.await();
}
}
catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
return extract();
}
finally {
lock.unlock();
}
}
/**
* Adds the specified element to the tail of this queue, waiting if
* necessary for space to become available.
*
* @param o the element to add
* @throws InterruptedException if interrupted while waiting.
* @throws NullPointerException if the specified element is null.
*/
public void put(E o) throws InterruptedException {
if (o == null) {
throw new NullPointerException();
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
while (movingBackToLowMark || count == items.length) {
notFull.await();
}
}
catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
insert(o);
}
finally {
lock.unlock();
}
}
/**
* Like {@link #put(Object)}, but for multiple entries.
*/
public void put(List objects) throws InterruptedException {
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
for (int i = 0; i < objects.size(); i++) {
E o = objects.get(i);
while (movingBackToLowMark || count == items.length) {
notFull.await();
}
insert(o);
}
}
catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
}
finally {
lock.unlock();
}
}
/**
* @return an approximative number of elements in this queue.
*/
public int size() {
return count;
}
// this doc comment is a modified copy of the inherited doc comment,
// without the reference to unlimited queues.
/**
* Returns the number of 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 size of this queue.
* Note that you cannot always tell if
* an attempt to add an element will succeed by
* inspecting remainingCapacity because it may be the
* case that a waiting consumer is ready to take an
* element out of an otherwise full queue.
*/
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.length - count;
}
finally {
lock.unlock();
}
}
public boolean contains(Object o) {
if (o == null) {
return false;
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
while (k++ < count) {
if (o.equals(items[i])) {
return true;
}
i = inc(i);
}
return false;
}
finally {
lock.unlock();
}
}
public Object[] toArray() {
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] a = new Object[count];
int k = 0;
int i = takeIndex;
while (k < count) {
a[k++] = items[i];
i = inc(i);
}
return a;
}
finally {
lock.unlock();
}
}
public T[] toArray(T[] a) {
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (a.length < count) {
a = (T[]) java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(),
count
);
}
int k = 0;
int i = takeIndex;
while (k < count) {
a[k++] = (T) items[i];
i = inc(i);
}
if (a.length > count) {
a[count] = null;
}
return a;
}
finally {
lock.unlock();
}
}
public String toString() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return super.toString();
}
finally {
lock.unlock();
}
}
/**
* Atomically removes all of the elements from this queue.
* The queue will be empty after this call returns.
*/
public void clear() {
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = count;
while (k-- > 0) {
items[i] = null;
i = inc(i);
}
count = 0;
putIndex = 0;
takeIndex = 0;
notFull.signalAll();
}
finally {
lock.unlock();
}
}
public int drainTo(Collection c) {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int n = 0;
int max = count;
while (n < max) {
c.add(items[i]);
items[i] = null;
i = inc(i);
++n;
}
if (n > 0) {
count = 0;
putIndex = 0;
takeIndex = 0;
notFull.signalAll();
}
return n;
}
finally {
lock.unlock();
}
}
public int drainTo(Collection c, int maxElements) {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
if (maxElements <= 0) {
return 0;
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int n = 0;
int max = (maxElements < count) ? maxElements : count;
while (n < max) {
c.add(items[i]);
items[i] = null;
i = inc(i);
++n;
}
if (n > 0) {
count -= n;
takeIndex = i;
notFull.signalAll();
}
return n;
}
finally {
lock.unlock();
}
}
/**
* Same as drainTo, but blocks until at least one element is available.
*/
public int blockingDrainTo(Collection c, int maxElements) throws InterruptedException {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
if (maxElements <= 0) {
return 0;
}
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (count == 0) {
notEmpty.await();
}
int i = takeIndex;
int n = 0;
int max = (maxElements < count) ? maxElements : count;
while (n < max) {
c.add(items[i]);
items[i] = null;
i = inc(i);
++n;
}
if (n > 0) {
count -= n;
takeIndex = i;
wakeupProducersIfNeeded();
}
return n;
}
catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
finally {
lock.unlock();
}
}
/**
* Returns an iterator over the elements in this queue in proper sequence.
* The returned Iterator is a "weakly consistent" iterator that
* will never throw {@link java.util.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 iterator() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return new Itr();
}
finally {
lock.unlock();
}
}
/**
* Iterator for ArrayBlockingQueue
*/
private class Itr implements Iterator {
/**
* Index of element to be returned by next,
* or a negative number if no such.
*/
private int nextIndex;
/**
* nextItem holds on to item fields because once we claim
* that an element exists in hasNext(), we must return it in
* the following next() call even if it was in the process of
* being removed when hasNext() was called.
*/
private E nextItem;
/**
* Index of element returned by most recent call to next.
* Reset to -1 if this element is deleted by a call to remove.
*/
private int lastRet;
Itr() {
lastRet = -1;
if (count == 0) {
nextIndex = -1;
} else {
nextIndex = takeIndex;
nextItem = items[takeIndex];
}
}
public boolean hasNext() {
/*
* No sync. We can return true by mistake here
* only if this iterator passed across threads,
* which we don't support anyway.
*/
return nextIndex >= 0;
}
/**
* Check whether nextIndex is valid; if so setting nextItem.
* Stops iterator when either hits putIndex or sees null item.
*/
private void checkNext() {
if (nextIndex == putIndex) {
nextIndex = -1;
nextItem = null;
} else {
nextItem = items[nextIndex];
if (nextItem == null) {
nextIndex = -1;
}
}
}
public E next() {
final ReentrantLock lock = FArrayBlockingQueue.this.lock;
lock.lock();
try {
if (nextIndex < 0) {
throw new NoSuchElementException();
}
lastRet = nextIndex;
E x = nextItem;
nextIndex = inc(nextIndex);
checkNext();
return x;
}
finally {
lock.unlock();
}
}
public void remove() {
final ReentrantLock lock = FArrayBlockingQueue.this.lock;
lock.lock();
try {
int i = lastRet;
if (i == -1) {
throw new IllegalStateException();
}
lastRet = -1;
int ti = takeIndex;
removeAt(i);
// back up cursor (reset to front if was first element)
nextIndex = (i == ti) ? takeIndex : i;
checkNext();
}
finally {
lock.unlock();
}
}
}
}