Class LinkedTransferQueue<E>
- Type Parameters:
E
- the type of elements held in this collection
- All Implemented Interfaces:
Serializable
,Iterable<E>
,Collection<E>
,BlockingQueue<E>
,Queue<E>
,TransferQueue<E>
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.
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.
- Since:
- 1.7
- See Also:
-
Constructor Summary
ConstructorsConstructorDescriptionCreates an initially emptyLinkedTransferQueue
.LinkedTransferQueue
(Collection<? extends E> c) Creates aLinkedTransferQueue
initially containing the elements of the given collection, added in traversal order of the collection's iterator. -
Method Summary
Modifier and TypeMethodDescriptionboolean
Inserts the specified element at the tail of this queue.boolean
Returnstrue
if this queue contains the specified element.int
drainTo
(Collection<? super E> c) int
drainTo
(Collection<? super E> c, int maxElements) int
Returns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()
or timedpoll
.boolean
Returnstrue
if there is at least one consumer waiting to receive an element viaBlockingQueue.take()
or timedpoll
.boolean
isEmpty()
Returnstrue
if this queue contains no elements.iterator()
Returns an iterator over the elements in this queue in proper sequence, from head to tail.boolean
Inserts the specified element at the tail of this queue.boolean
Inserts the specified element at the tail of this queue.peek()
poll()
void
Inserts the specified element at the tail of this queue.int
Always returnsInteger.MAX_VALUE
because aLinkedTransferQueue
is not capacity constrained.boolean
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.take()
void
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.Methods inherited from class java.util.AbstractQueue
addAll, clear, element, remove
Methods inherited from class java.util.AbstractCollection
containsAll, removeAll, retainAll, toArray, toArray, toString
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Collection
addAll, clear, containsAll, equals, hashCode, parallelStream, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray
-
Constructor Details
-
LinkedTransferQueue
public LinkedTransferQueue()Creates an initially emptyLinkedTransferQueue
. -
LinkedTransferQueue
Creates aLinkedTransferQueue
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- Throws:
NullPointerException
- if the specified collection or any of its elements are null
-
-
Method Details
-
put
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block.- Specified by:
put
in interfaceBlockingQueue<E>
- Throws:
NullPointerException
- if the specified element is null
-
offer
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block or returnfalse
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Returns:
true
(as specified byinvalid reference
BlockingQueue.offer
- Throws:
NullPointerException
- if the specified element is null
-
offer
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never returnfalse
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Specified by:
offer
in interfaceQueue<E>
- Returns:
true
(as specified byQueue.offer(E)
)- Throws:
NullPointerException
- if the specified element is null
-
add
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throwIllegalStateException
or returnfalse
.- Specified by:
add
in interfaceBlockingQueue<E>
- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceQueue<E>
- Overrides:
add
in classAbstractQueue<E>
- Returns:
true
(as specified byCollection.add(E)
)- Throws:
NullPointerException
- if the specified element is null
-
tryTransfer
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 timedpoll
), otherwise returningfalse
without enqueuing the element.- Specified by:
tryTransfer
in interfaceTransferQueue<E>
- Parameters:
e
- the element to transfer- Returns:
true
if the element was transferred, elsefalse
- Throws:
NullPointerException
- if the specified element is null
-
transfer
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 timedpoll
), else inserts the specified element at the tail of this queue and waits until the element is received by a consumer.- Specified by:
transfer
in interfaceTransferQueue<E>
- Parameters:
e
- the element to transfer- Throws:
NullPointerException
- if the specified element is nullInterruptedException
- if interrupted while waiting, in which case the element is not left enqueued
-
tryTransfer
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 timedpoll
), else inserts the specified element at the tail of this queue and waits until the element is received by a consumer, returningfalse
if the specified wait time elapses before the element can be transferred.- Specified by:
tryTransfer
in interfaceTransferQueue<E>
- Parameters:
e
- the element to transfertimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if successful, orfalse
if the specified waiting time elapses before completion, in which case the element is not left enqueued- Throws:
NullPointerException
- if the specified element is nullInterruptedException
- if interrupted while waiting, in which case the element is not left enqueued
-
take
- Specified by:
take
in interfaceBlockingQueue<E>
- Throws:
InterruptedException
-
poll
- Specified by:
poll
in interfaceBlockingQueue<E>
- Throws:
InterruptedException
-
poll
-
drainTo
- Specified by:
drainTo
in interfaceBlockingQueue<E>
-
drainTo
- Specified by:
drainTo
in interfaceBlockingQueue<E>
-
iterator
Returns an iterator over the elements in this queue in proper sequence, from head to tail.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.- Specified by:
iterator
in interfaceCollection<E>
- Specified by:
iterator
in interfaceIterable<E>
- Specified by:
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this queue in proper sequence
-
peek
-
isEmpty
public boolean isEmpty()Returnstrue
if this queue contains no elements.- Specified by:
isEmpty
in interfaceCollection<E>
- Overrides:
isEmpty
in classAbstractCollection<E>
- Returns:
true
if this queue contains no elements
-
hasWaitingConsumer
public boolean hasWaitingConsumer()Description copied from interface:TransferQueue
Returnstrue
if there is at least one consumer waiting to receive an element viaBlockingQueue.take()
or timedpoll
. The return value represents a momentary state of affairs.- Specified by:
hasWaitingConsumer
in interfaceTransferQueue<E>
- Returns:
true
if there is at least one waiting consumer
-
size
public int size()Returns the number of elements in this queue. If this queue contains more thanInteger.MAX_VALUE
elements, returnsInteger.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.
- Specified by:
size
in interfaceCollection<E>
- Specified by:
size
in classAbstractCollection<E>
- Returns:
- the number of elements in this queue
-
getWaitingConsumerCount
public int getWaitingConsumerCount()Description copied from interface:TransferQueue
Returns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()
or timedpoll
. 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 forTransferQueue.hasWaitingConsumer()
.- Specified by:
getWaitingConsumerCount
in interfaceTransferQueue<E>
- Returns:
- the number of consumers waiting to receive elements
-
remove
Removes a single instance of the specified element from this queue, if it is present. More formally, removes an elemente
such thato.equals(e)
, if this queue contains one or more such elements. Returnstrue
if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).- Specified by:
remove
in interfaceBlockingQueue<E>
- Specified by:
remove
in interfaceCollection<E>
- Overrides:
remove
in classAbstractCollection<E>
- Parameters:
o
- element to be removed from this queue, if present- Returns:
true
if this queue changed as a result of the call
-
contains
Returnstrue
if this queue contains the specified element. More formally, returnstrue
if and only if this queue contains at least one elemente
such thato.equals(e)
.- Specified by:
contains
in interfaceBlockingQueue<E>
- Specified by:
contains
in interfaceCollection<E>
- Overrides:
contains
in classAbstractCollection<E>
- Parameters:
o
- object to be checked for containment in this queue- Returns:
true
if this queue contains the specified element
-
remainingCapacity
public int remainingCapacity()Always returnsInteger.MAX_VALUE
because aLinkedTransferQueue
is not capacity constrained.- Specified by:
remainingCapacity
in interfaceBlockingQueue<E>
- Returns:
Integer.MAX_VALUE
(as specified byinvalid reference
BlockingQueue#remainingCapacity()
-