jdk.util.concurrent.ConcurrentLinkedQueue — clojure-interop/java.util.concurrent 1.0.5

An unbounded thread-safe java.util.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. Like most other concurrent collection implementations, this class does not permit the use of null elements.

This implementation employs an efficient non-blocking 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.

Iterators are weakly consistent, returning elements reflecting the state of the queue at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations. Elements contained in the queue since the creation of the iterator will be returned exactly once.

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, and so may report inaccurate results if this collection is modified during traversal. Additionally, the bulk operations addAll, removeAll, retainAll, containsAll, equals, and toArray are not guaranteed to be performed atomically. For example, an iterator operating concurrently with an addAll operation might view only some of the added elements.

This class and its iterator implement all of the optional methods of the Queue 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.

->concurrent-linked-queue clj

(->concurrent-linked-queue)

(->concurrent-linked-queue c)

Constructor.

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 - java.util.Collection

throws: java.lang.NullPointerException - if the specified collection or any of its elements are null

add clj

(add this e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throw IllegalStateException or return false.

e - the element to add - E

returns: true (as specified by Collection.add(E)) - boolean

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

add-all clj

(add-all this c)

Appends all of the elements in the specified collection to the end of this queue, in the order that they are returned by the specified collection's iterator. Attempts to addAll of a queue to itself result in IllegalArgumentException.

c - the elements to be inserted into this queue - java.util.Collection

returns: true if this queue changed as a result of the call - boolean

throws: java.lang.NullPointerException - if the specified collection or any of its elements are null

contains clj

(contains this 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 - java.lang.Object

returns: true if this queue contains the specified element - boolean

empty? clj

(empty? this)

Returns true if this queue contains no elements.

returns: true if this queue contains no elements - boolean

iterator clj

(iterator this)

Returns an iterator over the elements in this queue in proper sequence. The elements will be returned in order from first (head) to last (tail).

The returned iterator is weakly consistent.

returns: an iterator over the elements in this queue in proper sequence - java.util.Iterator<E>

offer clj

(offer this e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never return false.

e - the element to add - E

returns: true (as specified by Queue.offer(E)) - boolean

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

peek clj

(peek this)

Description copied from interface: Queue

returns: the head of this queue, or null if this queue is empty - E

poll clj

(poll this)

Description copied from interface: Queue

returns: the head of this queue, or null if this queue is empty - E

remove clj

(remove this 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 - java.lang.Object

returns: true if this queue changed as a result of the call - boolean

size clj

(size this)

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. Additionally, if elements are added or removed during execution of this method, the returned result may be inaccurate. Thus, this method is typically not very useful in concurrent applications.

returns: the number of elements in this queue - int

spliterator clj

(spliterator this)

Returns a Spliterator over the elements in this queue.

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator.CONCURRENT, Spliterator.ORDERED, and Spliterator.NONNULL.

returns: a Spliterator over the elements in this queue - java.util.Spliterator<E>

to-array clj

(to-array this)

(to-array this a)

Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array. 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.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:

String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

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 - T[]

returns: an array containing all of the elements in this queue - <T> T[]

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