co.paralleluniverse.concurrent.util

Class DelayQueue<E extends java.util.concurrent.Delayed>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

co.paralleluniverse.concurrent.util.DelayQueue<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

java.lang.Iterable<E>, java.util.Collection<E>, java.util.concurrent.BlockingQueue<E>, java.util.Queue<E>

public class DelayQueue<E extends java.util.concurrent.Delayed>
extends java.util.AbstractQueue<E>
implements java.util.concurrent.BlockingQueue<E>

An unbounded blocking queue of Delayed elements, in which an element can only be taken when its delay has expired. The head of the queue is that Delayed element whose delay expired furthest in the past. If no delay has expired there is no head and poll will return null. Expiration occurs when an element's getDelay(TimeUnit.NANOSECONDS) method returns a value less than or equal to zero. Even though unexpired elements cannot be removed using take or poll, they are otherwise treated as normal elements. For example, the size method returns the count of both expired and unexpired elements. This queue does not permit null elements.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

This class is a member of the Java Collections Framework.

Since:

1.5

Constructor Summary

Constructors

Constructor and Description
DelayQueue() Creates a new DelayQueue that is initially empty.
DelayQueue(java.util.Collection<? extends E> c) Creates a DelayQueue initially containing the elements of the given collection of Delayed instances.

Method Summary

Modifier and Type	Method and Description
boolean	add(E e) Inserts the specified element into this delay queue.
void	clear() Atomically removes all of the elements from this delay queue.
int	drainTo(java.util.Collection<? super E> c)
int	drainTo(java.util.Collection<? super E> c, int maxElements)
java.util.Iterator<E>	iterator() Returns an iterator over all the elements (both expired and unexpired) in this queue.
boolean	offer(E e) Inserts the specified element into this delay queue.
boolean	offer(E e, long timeout, java.util.concurrent.TimeUnit unit) Inserts the specified element into this delay queue.
E	peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll() Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired delay.
E	poll(long timeout, java.util.concurrent.TimeUnit unit) Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue, or the specified wait time expires.
void	put(E e) Inserts the specified element into this delay queue.
int	remainingCapacity() Always returns Integer.MAX_VALUE because a DelayQueue is not capacity constrained.
boolean	remove(java.lang.Object o) Removes a single instance of the specified element from this queue, if it is present, whether or not it has expired.
int	size()
E	take() Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue.
java.lang.Object[]	toArray() Returns an array containing all of the elements in this queue.
<T> T[]	toArray(T[] a) Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.

Methods inherited from class java.util.AbstractQueue

addAll, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, isEmpty, removeAll, retainAll, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.concurrent.BlockingQueue

contains

Methods inherited from interface java.util.Queue

element, remove

Methods inherited from interface java.util.Collection

addAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, stream

Methods inherited from interface java.lang.Iterable

forEach

Constructor Detail

DelayQueue

public DelayQueue()

Creates a new DelayQueue that is initially empty.

DelayQueue

public DelayQueue(java.util.Collection<? extends E> c)

Creates a DelayQueue initially containing the elements of the given collection of Delayed instances.

Parameters:

c - the collection of elements to initially contain

Throws:

java.lang.NullPointerException - if the specified collection or any of its elements are null

Method Detail

add

public boolean add(E e)

Inserts the specified element into this delay queue.

Specified by:

add in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Specified by:

add in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Specified by:

add in interface java.util.Queue<E extends java.util.concurrent.Delayed>

Overrides:

add in class java.util.AbstractQueue<E extends java.util.concurrent.Delayed>

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(E))

Throws:

java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(E e)

Inserts the specified element into this delay queue.

Specified by:

offer in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Specified by:

offer in interface java.util.Queue<E extends java.util.concurrent.Delayed>

Parameters:

e - the element to add

Returns:

true

Throws:

java.lang.NullPointerException - if the specified element is null

put

public void put(E e)

Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.

Specified by:

put in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Parameters:

e - the element to add

Throws:

java.lang.NullPointerException

offer

public boolean offer(E e,
                     long timeout,
                     java.util.concurrent.TimeUnit unit)

Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.

Specified by:

offer in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Parameters:

e - the element to add

timeout - This parameter is ignored as the method never blocks

unit - This parameter is ignored as the method never blocks

Returns:

true

Throws:

java.lang.NullPointerException

poll

public E poll()

Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired delay.

Specified by:

poll in interface java.util.Queue<E extends java.util.concurrent.Delayed>

Returns:

the head of this queue, or null if this queue has no elements with an expired delay

take

public E take()
       throws java.lang.InterruptedException

Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue.

Specified by:

take in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Returns:

the head of this queue

Throws:

java.lang.InterruptedException

poll

public E poll(long timeout,
              java.util.concurrent.TimeUnit unit)
       throws java.lang.InterruptedException

Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue, or the specified wait time expires.

Specified by:

poll in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Returns:

the head of this queue, or null if the specified waiting time elapses before an element with an expired delay becomes available

Throws:

java.lang.InterruptedException

peek

public E peek()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. Unlike poll, if no expired elements are available in the queue, this method returns the element that will expire next, if one exists.

Specified by:

peek in interface java.util.Queue<E extends java.util.concurrent.Delayed>

Returns:

the head of this queue, or null if this queue is empty.

size

public int size()

Specified by:

size in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Specified by:

size in class java.util.AbstractCollection<E extends java.util.concurrent.Delayed>

drainTo

public int drainTo(java.util.Collection<? super E> c)

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Throws:

java.lang.UnsupportedOperationException

java.lang.ClassCastException

java.lang.NullPointerException

java.lang.IllegalArgumentException

drainTo

public int drainTo(java.util.Collection<? super E> c,
                   int maxElements)

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Throws:

java.lang.UnsupportedOperationException

java.lang.ClassCastException

java.lang.NullPointerException

java.lang.IllegalArgumentException

clear

public void clear()

Atomically removes all of the elements from this delay queue. The queue will be empty after this call returns. Elements with an unexpired delay are not waited for; they are simply discarded from the queue.

Specified by:

clear in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Overrides:

clear in class java.util.AbstractQueue<E extends java.util.concurrent.Delayed>

remainingCapacity

public int remainingCapacity()

Always returns Integer.MAX_VALUE because a DelayQueue is not capacity constrained.

Specified by:

remainingCapacity in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Returns:

Integer.MAX_VALUE

toArray

public java.lang.Object[] toArray()

Returns an array containing all of the elements in this queue. The returned array elements are in no particular order.

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.

Specified by:

toArray in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Overrides:

toArray in class java.util.AbstractCollection<E extends java.util.concurrent.Delayed>

Returns:

an array containing all of the elements in this queue

toArray

public <T> T[] toArray(T[] a)

Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array. The returned array elements are in no particular order. 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 null.

Like the 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.

The following code can be used to dump a delay queue into a newly allocated array of Delayed:

     Delayed[] a = q.toArray(new Delayed[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Overrides:

toArray in class java.util.AbstractCollection<E extends java.util.concurrent.Delayed>

Parameters:

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

Returns:

an array containing all of the elements in this queue

Throws:

java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

java.lang.NullPointerException - if the specified array is null

remove

public boolean remove(java.lang.Object o)

Removes a single instance of the specified element from this queue, if it is present, whether or not it has expired.

Specified by:

remove in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Specified by:

remove in interface java.util.concurrent.BlockingQueue<E extends java.util.concurrent.Delayed>

Overrides:

remove in class java.util.AbstractCollection<E extends java.util.concurrent.Delayed>

iterator

public java.util.Iterator<E> iterator()

Returns an iterator over all the elements (both expired and unexpired) in this queue. The iterator does not return the elements in any particular order.

The returned iterator is a "weakly consistent" iterator that will never throw 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.

Specified by:

iterator in interface java.lang.Iterable<E extends java.util.concurrent.Delayed>

Specified by:

iterator in interface java.util.Collection<E extends java.util.concurrent.Delayed>

Specified by:

iterator in class java.util.AbstractCollection<E extends java.util.concurrent.Delayed>

Returns:

an iterator over the elements in this queue