java.util.concurrent.ConcurrentLinkedQueue<E>
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 implements all of the optional methods
of the Collection and Iterator interfaces.
Summary
Public Constructors
Public Methods
add,
addAll,
clear,
contains,
containsAll,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray,
toString
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
add,
addAll,
clear,
contains,
containsAll,
equals,
hashCode,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray
Methods inherited
from interface
java.util.Queue
Details
Public Constructors
public
ConcurrentLinkedQueue()
Creates a ConcurrentLinkedQueue that is initially empty.
public
ConcurrentLinkedQueue(Collection<? extends E> c)
Creates a
ConcurrentLinkedQueue
initially containing the elements of the given collection,
added in traversal order of the collection's iterator.
Parameters
c
| the collection of elements to initially contain |
Public Methods
public
boolean
add(E o)
Adds the specified element to the tail of this queue.
Returns
- true (as per the general contract of
Collection.add).
public
boolean
contains(Object o)
Searches this Collection for the specified object.
Parameters
o
| the object to search for |
Returns
- true if
object
is an element of this Collection,
false otherwise
public
boolean
isEmpty()
Returns true if the collection has no element, otherwise false.
Returns
- true if the collection has no element.
public
Iterator<E>
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
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.
Returns
- an iterator over the elements in this queue in proper sequence.
public
boolean
offer(E o)
Inserts the specified element to the tail of this queue.
Returns
- true (as per the general contract of
Queue.offer).
public
E
peek()
Gets but not removes the element in the head of the queue, or throws
exception if there is no element in the queue.
public
E
poll()
Gets and removes the element in the head of the queue, or returns null if
there is no element in the queue.
public
boolean
remove(Object o)
Removes the first occurrence of the specified object from this
Collection. This operation traverses over the collection, looking
for the specified object. Once the object is found, the object will
be removed from the collection using the iterator's remove method.
This collection will throw an UnsupportedOperationException if the
iterator returned does not implement remove method, and the specified
object is in this collection.
Returns
- true if this Collection is modified, false otherwise
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.
Returns
- the number of elements in this queue.
public
T[]
toArray(T[] a)
Returns an array containing all elements contained in this Collection. If
the specified array is large enough to hold the elements, the specified
array is used, otherwise an array of the same type is created. If the
specified array is used and is larger than this Collection, the array
element following the collection elements is set to null.
Returns
- an array of the elements from this Collection
public
Object[]
toArray()
Returns a new array containing all elements contained in this Collection.
All the elements in the array will not be referenced by the collection.
The elements in the returned array will be sorted to the same order as
those returned by the iterator of this collection itself if the collection
guarantees the order.
Returns
- an array of the elements from this Collection