edu.emory.mathcs.util.concurrent
Class DelayQueue

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--edu.emory.mathcs.util.AbstractQueue
              |
              +--edu.emory.mathcs.util.concurrent.DelayQueue
All Implemented Interfaces:
BlockingQueue, java.util.Collection, Queue

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. 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
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
 boolean add(java.lang.Object o)
          Adds the specified element to this 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 into 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 into the given collection.
 java.util.Iterator iterator()
          Returns an iterator over the elements in this queue.
 boolean offer(java.lang.Object o)
          Inserts the specified element into this delay queue.
 boolean offer(java.lang.Object o, 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, returning null if this queue has no elements with an unexpired delay.
 java.lang.Object poll()
          Retrieves and removes the head of this queue, or null if this queue has no elements with an unexpired delay.
 java.lang.Object poll(long timeout, TimeUnit unit)
          Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements with an unexpired delay are present on this queue.
 void put(java.lang.Object o)
          Adds the specified element to 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.
 int size()
           
 java.lang.Object take()
          Retrieves and removes the head of this queue, waiting if no elements with an unexpired delay are present on this queue.
 java.lang.Object[] toArray()
           
 java.lang.Object[] toArray(java.lang.Object[] array)
           
 
Methods inherited from class edu.emory.mathcs.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.util.Queue
element, remove
 
Methods inherited from interface java.util.Collection
addAll, contains, 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
Throws:
java.lang.NullPointerException - if c or any element within it is null
Method Detail

offer

public boolean offer(java.lang.Object o)
Inserts the specified element into this delay queue.

Specified by:
offer in interface BlockingQueue
Parameters:
o - the element to add
Returns:
true
Throws:
java.lang.NullPointerException - if the specified element is null.

put

public void put(java.lang.Object o)
Adds the specified element to this delay queue. As the queue is unbounded this method will never block.

Specified by:
put in interface BlockingQueue
Parameters:
o - the element to add
Throws:
java.lang.NullPointerException - if the specified element is null.

offer

public boolean offer(java.lang.Object o,
                     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:
o - 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.

add

public boolean add(java.lang.Object o)
Adds the specified element to this queue.

Specified by:
add in interface BlockingQueue
Overrides:
add in class AbstractQueue
Parameters:
o - the element to add
Returns:
true (as per the general contract of Collection.add).
Throws:
java.lang.NullPointerException - if the specified element is null.

take

public java.lang.Object take()
                      throws java.lang.InterruptedException
Retrieves and removes the head of this queue, waiting if no elements with an unexpired delay are present 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 up to the specified wait time if no elements with an unexpired delay are present on this queue.

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 unexpired delay is present.
Throws:
java.lang.InterruptedException - if interrupted while waiting.

poll

public java.lang.Object poll()
Retrieves and removes the head of this queue, or null if this queue has no elements with an unexpired delay.

Specified by:
poll in interface Queue
Returns:
the head of this queue, or null if this queue has no elements with an unexpired delay.

peek

public java.lang.Object peek()
Retrieves, but does not remove, the head of this queue, returning null if this queue has no elements with an unexpired delay.

Specified by:
peek in interface Queue
Returns:
the head of this queue, or null if this queue has no elements with an unexpired delay.

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 into 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.

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 into 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.

clear

public void clear()
Atomically removes all of the elements from this delay queue. The queue will be empty after this call returns.

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()
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray(java.lang.Object[] array)
Specified by:
toArray in interface java.util.Collection
Overrides:
toArray in class java.util.AbstractCollection

remove

public boolean remove(java.lang.Object o)
Removes a single instance of the specified element from this queue, if it is present.

Specified by:
remove in interface java.util.Collection
Overrides:
remove in class java.util.AbstractCollection

iterator

public java.util.Iterator iterator()
Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order. The returned iterator is a thread-safe "fast-fail" iterator that will throw ConcurrentModificationException upon detected interference.

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.