LinkedTransferQueue
public
class
LinkedTransferQueue
extends AbstractQueue<E>
implements
TransferQueue<E>,
Serializable
java.lang.Object | |||
↳ | java.util.AbstractCollection<E> | ||
↳ | java.util.AbstractQueue<E> | ||
↳ | java.util.concurrent.LinkedTransferQueue<E> |
An unbounded TransferQueue
based on linked nodes.
This queue orders elements FIFO (first-in-first-out) with respect
to any given producer. The head of the queue is that
element that has been on the queue the longest time for some
producer. The tail of the queue is that element that has
been on the queue the shortest time for some producer.
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.
Bulk operations that add, remove, or examine multiple elements,
such as AbstractQueue.addAll(Collection)
, removeIf(Predicate)
or forEach(Consumer)
,
are not guaranteed to be performed atomically.
For example, a forEach
traversal concurrent with an addAll
operation might observe only some of the added 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
LinkedTransferQueue
happen-before
actions subsequent to the access or removal of that element from
the LinkedTransferQueue
in another thread.
This class is a member of the Java Collections Framework.
Summary
Public constructors | |
---|---|
LinkedTransferQueue()
Creates an initially empty |
|
LinkedTransferQueue(Collection<? extends E> c)
Creates a |
Public methods | |
---|---|
boolean
|
add(E e)
Inserts the specified element at the tail of this queue. |
void
|
clear()
Removes all of the elements from this queue. |
boolean
|
contains(Object o)
Returns |
int
|
drainTo(Collection<? super E> c, int maxElements)
Removes at most the given number of available elements from this queue and adds them to the given collection. |
int
|
drainTo(Collection<? super E> c)
Removes all available elements from this queue and adds them to the given collection. |
void
|
forEach(Consumer<? super E> action)
|
int
|
getWaitingConsumerCount()
Returns an estimate of the number of consumers waiting to
receive elements via |
boolean
|
hasWaitingConsumer()
Returns |
boolean
|
isEmpty()
Returns |
Iterator<E>
|
iterator()
Returns an iterator over the elements in this queue in proper sequence. |
boolean
|
offer(E e, long timeout, TimeUnit unit)
Inserts the specified element at the tail of this queue. |
boolean
|
offer(E e)
Inserts the specified element at the tail of this queue. |
E
|
peek()
Retrieves, but does not remove, the head of this queue,
or returns |
E
|
poll(long timeout, TimeUnit unit)
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available. |
E
|
poll()
Retrieves and removes the head of this queue,
or returns |
void
|
put(E e)
Inserts the specified element at the tail of this queue. |
int
|
remainingCapacity()
Always returns |
boolean
|
remove(Object o)
Removes a single instance of the specified element from this queue, if it is present. |
boolean
|
removeAll(Collection<?> c)
Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
boolean
|
removeIf(Predicate<? super E> filter)
Removes all of the elements of this collection that satisfy the given predicate. |
boolean
|
retainAll(Collection<?> c)
Retains only the elements in this collection that are contained in the specified collection (optional operation). |
int
|
size()
Returns the number of elements in this queue. |
Spliterator<E>
|
spliterator()
Returns a |
E
|
take()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available. |
Object[]
|
toArray()
Returns an array containing all of the elements in this queue, in proper sequence. |
<T>
T[]
|
toArray(T[] 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. |
String
|
toString()
Returns a string representation of this collection. |
void
|
transfer(E e)
Transfers the element to a consumer, waiting if necessary to do so. |
boolean
|
tryTransfer(E e)
Transfers the element to a waiting consumer immediately, if possible. |
boolean
|
tryTransfer(E e, long timeout, TimeUnit unit)
Transfers the element to a consumer if it is possible to do so before the timeout elapses. |
Inherited methods | |
---|---|
Public constructors
LinkedTransferQueue
public LinkedTransferQueue ()
Creates an initially empty LinkedTransferQueue
.
LinkedTransferQueue
public LinkedTransferQueue (Collection<? extends E> c)
Creates a LinkedTransferQueue
initially containing the elements of the given collection,
added in traversal order of the collection's iterator.
Parameters | |
---|---|
c |
Collection : the collection of elements to initially contain |
Throws | |
---|---|
NullPointerException |
if the specified collection or any of its elements are null |
Public methods
add
public boolean add (E 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
.
Parameters | |
---|---|
e |
E : the element to add |
Returns | |
---|---|
boolean |
true (as specified by Collection#add ) |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
clear
public void clear ()
Removes all of the elements from this queue. The queue will be empty after this call returns.
This implementation repeatedly invokes poll
until it
returns null
.
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)
.
Parameters | |
---|---|
o |
Object : object to be checked for containment in this queue |
Returns | |
---|---|
boolean |
true if this queue contains the specified element |
drainTo
public int drainTo (Collection<? super E> c, int maxElements)
Removes at most the given number of available elements from
this queue and adds them to 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.
Parameters | |
---|---|
c |
Collection : the collection to transfer elements into |
maxElements |
int : the maximum number of elements to transfer |
Returns | |
---|---|
int |
the number of elements transferred |
Throws | |
---|---|
NullPointerException |
|
IllegalArgumentException |
drainTo
public int drainTo (Collection<? super E> c)
Removes all available elements from this queue and adds them
to 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.
Parameters | |
---|---|
c |
Collection : the collection to transfer elements into |
Returns | |
---|---|
int |
the number of elements transferred |
Throws | |
---|---|
NullPointerException |
|
IllegalArgumentException |
forEach
public void forEach (Consumer<? super E> action)
Parameters | |
---|---|
action |
Consumer |
Throws | |
---|---|
NullPointerException |
getWaitingConsumerCount
public int getWaitingConsumerCount ()
Returns an estimate of the number of consumers waiting to
receive elements via BlockingQueue.take()
or timed
poll
. The return value is an
approximation of a momentary state of affairs, that may be
inaccurate if consumers have completed or given up waiting.
The value may be useful for monitoring and heuristics, but
not for synchronization control. Implementations of this
method are likely to be noticeably slower than those for
hasWaitingConsumer()
.
Returns | |
---|---|
int |
the number of consumers waiting to receive elements |
hasWaitingConsumer
public boolean hasWaitingConsumer ()
Returns true
if there is at least one consumer waiting
to receive an element via BlockingQueue.take()
or
timed poll
.
The return value represents a momentary state of affairs.
Returns | |
---|---|
boolean |
true if there is at least one waiting consumer |
isEmpty
public boolean isEmpty ()
Returns true
if this queue contains no elements.
Returns | |
---|---|
boolean |
true if this queue contains no elements |
iterator
public Iterator<E> iterator ()
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 | |
---|---|
Iterator<E> |
an iterator over the elements in this queue in proper sequence |
offer
public boolean offer (E e, long timeout, TimeUnit unit)
Inserts the specified element at the tail of this queue.
As the queue is unbounded, this method will never block or
return false
.
Parameters | |
---|---|
e |
E : the element to add |
timeout |
long : how long to wait before giving up, in units of
unit |
unit |
TimeUnit : a TimeUnit determining how to interpret the
timeout parameter |
Returns | |
---|---|
boolean |
true (as specified by
BlockingQueue.offer ) |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
offer
public boolean offer (E e)
Inserts the specified element at the tail of this queue.
As the queue is unbounded, this method will never return false
.
Parameters | |
---|---|
e |
E : the element to add |
Returns | |
---|---|
boolean |
true (as specified by Queue#offer ) |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
peek
public E peek ()
Retrieves, but does not remove, the head of this queue,
or returns null
if this queue is empty.
Returns | |
---|---|
E |
the head of this queue, or null if this queue is empty |
poll
public E poll (long timeout, TimeUnit unit)
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
Parameters | |
---|---|
timeout |
long : how long to wait before giving up, in units of
unit |
unit |
TimeUnit : a TimeUnit determining how to interpret the
timeout parameter |
Returns | |
---|---|
E |
the head of this queue, or null if the
specified waiting time elapses before an element is available |
Throws | |
---|---|
InterruptedException |
poll
public E poll ()
Retrieves and removes the head of this queue,
or returns null
if this queue is empty.
Returns | |
---|---|
E |
the head of this queue, or null if this queue is empty |
put
public void put (E e)
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block.
Parameters | |
---|---|
e |
E : the element to add |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
remainingCapacity
public int remainingCapacity ()
Always returns Integer.MAX_VALUE
because a
LinkedTransferQueue
is not capacity constrained.
Returns | |
---|---|
int |
Integer.MAX_VALUE (as specified by
BlockingQueue#remainingCapacity() ) |
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).
Parameters | |
---|---|
o |
Object : element to be removed from this queue, if present |
Returns | |
---|---|
boolean |
true if this queue changed as a result of the call |
removeAll
public boolean removeAll (Collection<?> c)
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
Parameters | |
---|---|
c |
Collection : collection containing elements to be removed from this collection |
Returns | |
---|---|
boolean |
true if this collection changed as a result of the
call |
Throws | |
---|---|
NullPointerException |
removeIf
public boolean removeIf (Predicate<? super E> filter)
Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.
Parameters | |
---|---|
filter |
Predicate : a predicate which returns true for elements to be
removed |
Returns | |
---|---|
boolean |
true if any elements were removed |
Throws | |
---|---|
NullPointerException |
retainAll
public boolean retainAll (Collection<?> c)
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
Parameters | |
---|---|
c |
Collection : collection containing elements to be retained in this collection |
Returns | |
---|---|
boolean |
true if this collection changed as a result of the call |
Throws | |
---|---|
NullPointerException |
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.
Returns | |
---|---|
int |
the number of elements in this queue |
spliterator
public Spliterator<E> spliterator ()
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
.
Implementation Note:
- The
Spliterator
implementstrySplit
to permit limited parallelism.
Returns | |
---|---|
Spliterator<E> |
a Spliterator over the elements in this queue |
take
public E take ()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
Returns | |
---|---|
E |
the head of this queue |
Throws | |
---|---|
InterruptedException |
toArray
public Object[] toArray ()
Returns an array containing all of the elements in this queue, in proper sequence.
The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
Returns | |
---|---|
Object[] |
an array containing all of the elements in this queue |
toArray
public T[] toArray (T[] 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]);
toArray(new Object[0])
is identical in function to
toArray()
.
Parameters | |
---|---|
a |
T : 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 |
Returns | |
---|---|
T[] |
an array containing all of the elements in this queue |
Throws | |
---|---|
ArrayStoreException |
if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue |
NullPointerException |
if the specified array is null |
toString
public String toString ()
Returns a string representation of this collection. The string
representation consists of a list of the collection's elements in the
order they are returned by its iterator, enclosed in square brackets
("[]"
). Adjacent elements are separated by the characters
", "
(comma and space). Elements are converted to strings as
by String#valueOf(Object)
.
Returns | |
---|---|
String |
a string representation of this collection |
transfer
public void transfer (E e)
Transfers the element to a consumer, waiting if necessary to do so.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
take()
or timed poll
),
else inserts the specified element at the tail of this queue
and waits until the element is received by a consumer.
Parameters | |
---|---|
e |
E : the element to transfer |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
InterruptedException |
tryTransfer
public boolean tryTransfer (E e)
Transfers the element to a waiting consumer immediately, if possible.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
take()
or timed poll
),
otherwise returning false
without enqueuing the element.
Parameters | |
---|---|
e |
E : the element to transfer |
Returns | |
---|---|
boolean |
true if the element was transferred, else
false |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
tryTransfer
public boolean tryTransfer (E e, long timeout, TimeUnit unit)
Transfers the element to a consumer if it is possible to do so before the timeout elapses.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
take()
or timed poll
),
else inserts the specified element at the tail of this queue
and waits until the element is received by a consumer,
returning false
if the specified wait time elapses
before the element can be transferred.
Parameters | |
---|---|
e |
E : the element to transfer |
timeout |
long : how long to wait before giving up, in units of
unit |
unit |
TimeUnit : a TimeUnit determining how to interpret the
timeout parameter |
Returns | |
---|---|
boolean |
true if successful, or false if
the specified waiting time elapses before completion,
in which case the element is not left enqueued |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
InterruptedException |