netflix.ocelli.util.RandomBlockingQueue Maven / Gradle / Ivy
package netflix.ocelli.util;
import java.util.AbstractQueue;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
public class RandomBlockingQueue extends AbstractQueue {
/** The queued items */
private List items = new ArrayList();
private Random rand = new Random();
/** Main lock guarding all access */
final ReentrantLock lock;
/** Condition for waiting takes */
private final Condition notEmpty;
public RandomBlockingQueue() {
this(false);
}
public RandomBlockingQueue(boolean fair) {
lock = new ReentrantLock(fair);
notEmpty = lock.newCondition();
}
private static void checkNotNull(Object v) {
if (v == null)
throw new NullPointerException();
}
@SuppressWarnings("unchecked")
static E cast(Object item) {
return (E) item;
}
/**
* Inserts element into array
* Call only when holding lock.
*/
private void insert(E x) {
if (items.size() == 0) {
items.add(x);
}
else {
int index = rand.nextInt(items.size());
items.add(items.get(index));
items.set(index, x);
}
notEmpty.signal();
}
/**
* Extracts random element. Moves the last element to the spot where the random
* element was removed. This avoids having to shift all the items in the array.
*
* Call only when holding lock.
*/
private E extract() {
return items.remove(items.size()-1);
}
public boolean offer(E e) {
checkNotNull(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
insert(e);
return true;
} finally {
lock.unlock();
}
}
public void put(E e) throws InterruptedException {
offer(e);
}
public boolean offer(E e, long timeout, TimeUnit unit) {
offer(e);
return true;
}
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (items.size() == 0) ? null : extract();
} finally {
lock.unlock();
}
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (items.size() == 0)
notEmpty.await();
return extract();
} finally {
lock.unlock();
}
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (items.size() == 0) {
if (nanos <= 0)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
return extract();
} finally {
lock.unlock();
}
}
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (items.size() == 0) ? null : items.get(rand.nextInt(items.size()));
} finally {
lock.unlock();
}
}
// 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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.size();
} finally {
lock.unlock();
}
}
// 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.
*
* 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.
*/
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return Integer.MAX_VALUE - items.size();
} finally {
lock.unlock();
}
}
/**
* 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).
*
*
Removal of interior elements in circular array based queues
* is an intrinsically slow and disruptive operation, so should
* be undertaken only in exceptional circumstances, ideally
* only when the queue is known not to be accessible by other
* threads.
*
* @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;
final ReentrantLock lock = this.lock;
lock.lock();
try {
return this.items.remove(o);
} finally {
lock.unlock();
}
}
/**
* Returns {@code true} if this queue contains the specified element.
* More formally, returns {@code true} if and only if this queue contains
* at least one element {@code e} such that {@code o.equals(e)}.
*
* @param o object to be checked for containment in this queue
* @return {@code true} if this queue contains the specified element
*/
public boolean contains(Object o) {
if (o == null) return false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.contains(o);
} finally {
lock.unlock();
}
}
/**
* Returns an array containing all of the elements in this queue, in
* proper sequence.
*
*
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.
*
*
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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return this.items.toArray(new Object[items.size()]);
} finally {
lock.unlock();
}
}
/**
* 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.
*
*
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}.
*
*
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.
*
*
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}:
*
*
* String[] y = x.toArray(new String[0]);
*
* 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
*/
public T[] toArray(T[] a) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.toArray(a);
} finally {
lock.unlock();
}
}
public String toString() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.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 ReentrantLock lock = this.lock;
lock.lock();
try {
this.items.clear();
} finally {
lock.unlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection c) {
checkNotNull(c);
if (c == this)
throw new IllegalArgumentException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = this.items.size();
this.items.removeAll(c);
return n;
} finally {
lock.unlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection c, int maxElements) {
checkNotNull(c);
if (c == this)
throw new IllegalArgumentException();
if (maxElements <= 0)
return 0;
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (maxElements < this.items.size())
maxElements = this.items.size();
int n = this.items.size();
this.items.removeAll(c);
return n;
} finally {
lock.unlock();
}
}
/**
* Returns an iterator over the elements in this queue 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 queue in proper sequence
*/
public Iterator iterator() {
throw new UnsupportedOperationException();
}
}