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.
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 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.
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. |
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. |
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. |
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 | |
---|---|
From
class
java.util.AbstractQueue
| |
From
class
java.util.AbstractCollection
| |
From
class
java.lang.Object
| |
From
interface
java.util.Queue
| |
From
interface
java.util.Collection
| |
From
interface
java.util.concurrent.TransferQueue
| |
From
interface
java.lang.Iterable
| |
From
interface
java.util.concurrent.BlockingQueue
|
LinkedTransferQueue ()
Creates an initially empty LinkedTransferQueue
.
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 |
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 add(E) ) |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
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
|
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 |
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 |
int getWaitingConsumerCount ()
Returns an estimate of the number of consumers waiting to
receive elements via 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 |
boolean hasWaitingConsumer ()
Returns true
if there is at least one consumer waiting
to receive an element via take()
or
timed poll
.
The return value represents a momentary state of affairs.
Returns | |
---|---|
boolean |
true if there is at least one waiting consumer
|
boolean isEmpty ()
Returns true
if this queue contains no elements.
Returns | |
---|---|
boolean |
true if this queue contains no elements
|
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 |
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 |
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 offer(E) ) |
Throws | |
---|---|
NullPointerException |
if the specified element is null |
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
|
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 |
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
|
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 |
int remainingCapacity ()
Always returns Integer.MAX_VALUE
because a
LinkedTransferQueue
is not capacity constrained.
Returns | |
---|---|
int |
Integer.MAX_VALUE (as specified by
BlockingQueue.remainingCapacity )
|
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
|
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<E> spliterator ()
Returns a Spliterator
over the elements in this queue.
The returned spliterator is weakly consistent.
The Spliterator
reports CONCURRENT
,
ORDERED
, and NONNULL
.
Spliterator
implements trySplit
to permit limited
parallelism.Returns | |
---|---|
Spliterator<E> |
a Spliterator over the elements in this queue |
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 |
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 |
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]);
Note that 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 |
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 valueOf(Object)
.
Returns | |
---|---|
String |
a string representation of this collection |
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 |
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 |
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 |