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java.lang.Objectjava.util.AbstractCollection
org.apache.openjpa.lib.util.concurrent.ConcurrentLinkedQueue
public class ConcurrentLinkedQueue
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
Java Collections Framework.
Constructor Summary | |
---|---|
ConcurrentLinkedQueue()
|
|
ConcurrentLinkedQueue(java.util.Collection c)
Creates a ConcurrentLinkedQueue initially containing the elements of the given collection, added in traversal order of the collection's iterator. |
Method Summary | |
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boolean |
add(java.lang.Object e)
Inserts the specified element at the tail of this queue. |
boolean |
addAll(java.util.Collection c)
Adds all of the elements in the specified collection to this queue. |
void |
clear()
Removes all of the elements from this queue. |
boolean |
contains(java.lang.Object o)
Returns true if this queue contains the specified element. |
java.lang.Object |
element()
Retrieves, but does not remove, the head of this queue. |
boolean |
isEmpty()
Returns true if this queue contains no elements. |
java.util.Iterator |
iterator()
Returns an iterator over the elements in this queue in proper sequence. |
boolean |
offer(java.lang.Object e)
Inserts the specified element at the tail of this 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 is empty. |
java.lang.Object |
remove()
Retrieves and removes the head of this queue. |
boolean |
remove(java.lang.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. |
java.lang.Object[] |
toArray()
|
java.lang.Object[] |
toArray(java.lang.Object[] a)
|
Methods inherited from class java.util.AbstractCollection |
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containsAll, removeAll, retainAll, toString |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface org.apache.openjpa.lib.util.concurrent.Queue |
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element, remove |
Methods inherited from interface java.util.Collection |
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addAll, clear, containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray |
Constructor Detail |
---|
public ConcurrentLinkedQueue()
public ConcurrentLinkedQueue(java.util.Collection c)
c
- the collection of elements to initially contain
java.lang.NullPointerException
- if the specified collection or any
of its elements are nullMethod Detail |
---|
public boolean add(java.lang.Object e)
add
in interface java.util.Collection
add
in interface Queue
e
- the element to add
Collection.add(E)
)
java.lang.NullPointerException
- if the specified element is nullpublic boolean offer(java.lang.Object e)
offer
in interface Queue
e
- the element to add
Queue.offer(java.lang.Object)
)
java.lang.NullPointerException
- if the specified element is nullpublic java.lang.Object poll()
Queue
poll
in interface Queue
public java.lang.Object peek()
Queue
peek
in interface Queue
public boolean isEmpty()
isEmpty
in interface java.util.Collection
isEmpty
in class java.util.AbstractCollection
public int size()
size
in interface java.util.Collection
size
in class java.util.AbstractCollection
public boolean contains(java.lang.Object o)
contains
in interface java.util.Collection
contains
in class java.util.AbstractCollection
o
- object to be checked for containment in this queue
public boolean remove(java.lang.Object o)
remove
in interface java.util.Collection
remove
in class java.util.AbstractCollection
o
- element to be removed from this queue, if present
public java.util.Iterator iterator()
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.
iterator
in interface java.lang.Iterable
iterator
in interface java.util.Collection
iterator
in class java.util.AbstractCollection
public java.lang.Object remove()
poll
only in that it throws an exception if this
queue is empty. This implementation returns the result of poll
unless the queue is empty.
remove
in interface Queue
java.util.NoSuchElementException
- if this queue is emptypublic java.lang.Object element()
peek
only in that it throws an exception if
this queue is empty.
This implementation returns the result of peek
unless the queue is empty.
element
in interface Queue
java.util.NoSuchElementException
- if this queue is emptypublic void clear()
poll
until it
returns null.
clear
in interface java.util.Collection
clear
in class java.util.AbstractCollection
public boolean addAll(java.util.Collection c)
addAll
in interface java.util.Collection
addAll
in class java.util.AbstractCollection
c
- collection containing elements to be added to this queue
java.lang.ClassCastException
- if the class of an element of the specified
collection prevents it from being added to this queue
java.lang.NullPointerException
- if the specified collection contains a
null element and this queue does not permit null elements,
or if the specified collection is null
java.lang.IllegalArgumentException
- if some property of an element of the
specified collection prevents it from being added to this
queue, or if the specified collection is this queue
java.lang.IllegalStateException
- if not all the elements can be added at
this time due to insertion restrictionsadd(Object)
public java.lang.Object[] toArray()
toArray
in interface java.util.Collection
toArray
in class java.util.AbstractCollection
public java.lang.Object[] toArray(java.lang.Object[] a)
toArray
in interface java.util.Collection
toArray
in class java.util.AbstractCollection
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