edu.emory.mathcs.backport.java.util.concurrent
Class ConcurrentLinkedQueue
java.util.AbstractCollection
- Collection, Queue, java.io.Serializable
public class ConcurrentLinkedQueue
implements Queue, java.io.Serializable
An unbounded thread-safe
queue based on linked nodes.
This queue orders elements FIFO (first-in-first-out).
The
head of the queue is that element that has been on the
queue the longest time.
The
tail of the queue is that element that has been on the
queue the shortest time. New elements
are inserted at the tail of the queue, and the queue retrieval
operations obtain elements at the head of the queue.
A
ConcurrentLinkedQueue is an appropriate choice when
many threads will share access to a common collection.
This queue does not permit
null elements.
This implementation employs an efficient "wait-free"
algorithm based on one described in
Simple,
Fast, and Practical Non-Blocking and Blocking Concurrent Queue
Algorithms by Maged M. Michael and Michael L. Scott.
Beware that, unlike in most collections, the
size method
is
NOT a constant-time operation. Because of the
asynchronous nature of these queues, determining the current number
of elements requires a traversal of the elements.
This class and its iterator implement all of the
optional methods of the
Collection
and
Iterator
interfaces.
Memory consistency effects: As with other concurrent
collections, actions in a thread prior to placing an object into a
ConcurrentLinkedQueue
happen-before
actions subsequent to the access or removal of that element from
the
ConcurrentLinkedQueue
in another thread.
This class is a member of the
../../../../../../../../guide/collections/index.html">
Java Collections Framework.
ConcurrentLinkedQueue() - Creates a ConcurrentLinkedQueue that is initially empty.
|
ConcurrentLinkedQueue(Collection c) - Creates a ConcurrentLinkedQueue
initially containing the elements of the given collection,
added in traversal order of the collection's iterator.
|
boolean | add(Object e) - Inserts the specified element at the tail of this queue.
|
boolean | contains(Object o) - Returns true if this queue contains the specified element.
|
boolean | isEmpty() - Returns true if this queue contains no elements.
|
Iterator | iterator() - Returns an iterator over the elements in this queue in proper sequence.
|
boolean | offer(Object e) - Inserts the specified element at the tail of this queue.
|
Object | peek() - Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
|
Object | poll() - Retrieves and removes the head of this queue,
or returns null if this queue is empty.
|
boolean | remove(Object o) - Removes a single instance of the specified element from this queue,
if it is present.
|
int | size() - Returns the number of elements in this queue.
|
ConcurrentLinkedQueue
public ConcurrentLinkedQueue()
Creates a ConcurrentLinkedQueue that is initially empty.
ConcurrentLinkedQueue
public ConcurrentLinkedQueue(Collection c)
Creates a ConcurrentLinkedQueue
initially containing the elements of the given collection,
added in traversal order of the collection's iterator.
c
- the collection of elements to initially contain
add
public boolean add(Object e)
Inserts the specified element at the tail of this queue.
- add in interface Queue
- add in interface AbstractQueue
- true (as specified by
Collection.add
)
contains
public boolean contains(Object o)
Returns true if this queue contains the specified element.
More formally, returns true if and only if this queue contains
at least one element e such that o.equals(e).
o
- object to be checked for containment in this queue
- true if this queue contains the specified element
isEmpty
public boolean isEmpty()
Returns true if this queue contains no elements.
- true if this queue contains no elements
iterator
public Iterator iterator()
Returns an iterator over the elements in this queue in proper sequence.
The returned iterator is a "weakly consistent" iterator that
will never throw 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.
- an iterator over the elements in this queue in proper sequence
offer
public boolean offer(Object e)
Inserts the specified element at the tail of this queue.
- offer in interface Queue
peek
public Object peek()
Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
- peek in interface Queue
- the head of this queue, or null if this queue is empty
poll
public Object poll()
Retrieves and removes the head of this queue,
or returns null if this queue is empty.
- poll in interface Queue
- the head of this queue, or null if this queue is empty
remove
public boolean remove(Object o)
Removes a single instance of the specified element from this queue,
if it is present. More formally, removes an element e such
that o.equals(e), if this queue contains one or more such
elements.
Returns true if this queue contained the specified element
(or equivalently, if this queue changed as a result of the call).
o
- element to be removed from this queue, if present
- true if this queue changed as a result of the call
size
public int size()
Returns the number of elements in this queue. If this queue
contains more than
Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Beware that, unlike in most collections, this method is
NOT a constant-time operation. Because of the
asynchronous nature of these queues, determining the current
number of elements requires an O(n) traversal.
- the number of elements in this queue