edu.emory.mathcs.backport.java.util.concurrent

Class DelayQueue

java.lang.Object

java.util.AbstractCollection

edu.emory.mathcs.backport.java.util.AbstractCollection

edu.emory.mathcs.backport.java.util.AbstractQueue

edu.emory.mathcs.backport.java.util.concurrent.DelayQueue

All Implemented Interfaces:

BlockingQueue, Queue, java.lang.Iterable, java.util.Collection

public class DelayQueue
extends AbstractQueue
implements BlockingQueue

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

Author:

Doug Lea

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
boolean	add(java.lang.Object 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 c) Removes all available elements from this queue and adds them to the given collection.
int	drainTo(java.util.Collection c, int maxElements) Removes at most the given number of available elements from this queue and adds them to the given collection.
java.util.Iterator	iterator() Returns an iterator over all the elements (both expired and unexpired) in this queue.
boolean	offer(java.lang.Object e) Inserts the specified element into this delay queue.
boolean	offer(java.lang.Object e, long timeout, TimeUnit unit) Inserts the specified element into this delay queue.
java.lang.Object	peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
java.lang.Object	poll() Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired delay.
java.lang.Object	poll(long timeout, 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(java.lang.Object 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()
java.lang.Object	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.
java.lang.Object[]	toArray(java.lang.Object[] 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 edu.emory.mathcs.backport.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 edu.emory.mathcs.backport.java.util.concurrent.BlockingQueue

contains

Methods inherited from interface edu.emory.mathcs.backport.java.util.Queue

element, remove

Methods inherited from interface java.util.Collection

addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll

Constructor Detail

DelayQueue

public DelayQueue()

Creates a new DelayQueue that is initially empty.

DelayQueue

public DelayQueue(java.util.Collection 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(java.lang.Object e)

Inserts the specified element into this delay queue.

Specified by:

add in interface BlockingQueue

Specified by:

add in interface Queue

Specified by:

add in interface java.util.Collection

Overrides:

add in class AbstractQueue

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(java.lang.Object))

Throws:

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

offer

public boolean offer(java.lang.Object e)

Inserts the specified element into this delay queue.

Specified by:

offer in interface BlockingQueue

Specified by:

offer in interface Queue

Parameters:

e - the element to add

Returns:

true

Throws:

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

put

public void put(java.lang.Object e)

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

Specified by:

put in interface BlockingQueue

Parameters:

e - the element to add

Throws:

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

offer

public boolean offer(java.lang.Object e,
            long timeout,
            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 BlockingQueue

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 - if the specified element is null

poll

public java.lang.Object 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 Queue

Returns:

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

take

public java.lang.Object 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 BlockingQueue

Returns:

the head of this queue

Throws:

java.lang.InterruptedException - if interrupted while waiting

poll

public java.lang.Object poll(long timeout,
                    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 BlockingQueue

Parameters:

timeout - how long to wait before giving up, in units of unit

unit - a TimeUnit determining how to interpret the timeout parameter

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 - if interrupted while waiting

peek

public java.lang.Object 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 Queue

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

Specified by:

size in class java.util.AbstractCollection

drainTo

public int drainTo(java.util.Collection c)

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

java.lang.UnsupportedOperationException - if addition of elements is not supported by the specified collection

java.lang.ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

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

java.lang.IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

drainTo

public int drainTo(java.util.Collection c,
          int maxElements)

Description copied from interface: BlockingQueue

Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

java.lang.UnsupportedOperationException - if addition of elements is not supported by the specified collection

java.lang.ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

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

java.lang.IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

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

Overrides:

clear in class AbstractQueue

remainingCapacity

public int remainingCapacity()

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

Specified by:

remainingCapacity in interface BlockingQueue

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

Overrides:

toArray in class AbstractCollection

Returns:

an array containing all of the elements in this queue

toArray

public java.lang.Object[] toArray(java.lang.Object[] 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

Overrides:

toArray in class AbstractCollection

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 BlockingQueue

Specified by:

remove in interface java.util.Collection

Overrides:

remove in class java.util.AbstractCollection

Parameters:

o - element to be removed from this queue, if present

Returns:

true if this queue changed as a result of the call

iterator

public java.util.Iterator 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

Specified by:

iterator in interface java.util.Collection

Specified by:

iterator in class java.util.AbstractCollection

Returns:

an iterator over the elements in this queue