- Type Parameters:
E
- the type of elements held in this queue
- All Implemented Interfaces:
Serializable
,Iterable<E>
,Collection<E>
,BlockingQueue<E>
,TransferQueue<E>
,Queue<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, 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(java.util.Collection<? extends E>)
, removeIf(java.util.function.Predicate<? super E>)
or forEach(java.util.function.Consumer<? super E>)
,
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.
- Since:
- 1.7
- See Also:
-
Constructor Summary
ConstructorDescriptionCreates 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.void
clear()
Removes all of the elements from this queue.boolean
Returnstrue
if this queue contains the specified element.int
drainTo
(Collection<? super E> c) Removes all available elements from this queue and adds them to the given collection.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.void
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception.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.boolean
Inserts the specified element at the tail of this queue.boolean
Inserts the specified element at the tail of this queue.peek()
Retrieves, but does not remove, the head of this queue, or returnsnull
if this queue is empty.poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.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.boolean
removeAll
(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).boolean
Removes all of the elements of this collection that satisfy the given predicate (optional operation).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.Returns aSpliterator
over the elements in this queue.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.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 declared in class java.util.AbstractQueue
addAll, clear, element, remove
Methods declared in class java.util.AbstractCollection
containsAll, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, parallelStream, stream, 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
-
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.
- Specified by:
toArray
in interfaceCollection<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Returns:
- an array containing all of the elements in this queue
-
toArray
public <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. 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 ofString
:String[] y = x.toArray(new String[0]);
toArray(new Object[0])
is identical in function totoArray()
.- Specified by:
toArray
in interfaceCollection<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Type Parameters:
T
- the component type of the array to contain the collection- Parameters:
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- Returns:
- 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 queueNullPointerException
- if the specified array is null
-
spliterator
Returns aSpliterator
over the elements in this queue.The returned spliterator is weakly consistent.
The
Spliterator
reportsSpliterator.CONCURRENT
,Spliterator.ORDERED
, andSpliterator.NONNULL
.- Specified by:
spliterator
in interfaceCollection<E>
- Specified by:
spliterator
in interfaceIterable<E>
- Implementation Note:
- The
Spliterator
implementstrySplit
to permit limited parallelism. - Returns:
- a
Spliterator
over the elements in this queue - Since:
- 1.8
-
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>
- Parameters:
e
- the element to add- 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>
- Parameters:
e
- the element to addtimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
(as specified byBlockingQueue.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>
- Parameters:
e
- the element to add- 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>
- Parameters:
e
- the element to add- 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
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.- Specified by:
take
in interfaceBlockingQueue<E>
- Returns:
- the head of this queue
- Throws:
InterruptedException
- if interrupted while waiting
-
poll
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.- Specified by:
poll
in interfaceBlockingQueue<E>
- Parameters:
timeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- the head of this queue, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
poll
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in interfaceBlockingQueue<E>
- Parameters:
c
- the collection to transfer elements into- Returns:
- the number of elements transferred
- Throws:
NullPointerException
- if the specified collection is nullIllegalArgumentException
- if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in interfaceBlockingQueue<E>
- Parameters:
c
- the collection to transfer elements intomaxElements
- the maximum number of elements to transfer- Returns:
- the number of elements transferred
- Throws:
NullPointerException
- if the specified collection is nullIllegalArgumentException
- if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection
-
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.
- 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>
- 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 byBlockingQueue.remainingCapacity()
)
-
removeIf
Description copied from interface:Collection
Removes all of the elements of this collection that satisfy the given predicate (optional operation). Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIf
in interfaceCollection<E>
- Parameters:
filter
- a predicate which returnstrue
for elements to be removed- Returns:
true
if any elements were removed- Throws:
NullPointerException
- if the specified filter is null
-
removeAll
Description copied from class:AbstractCollection
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.- Specified by:
removeAll
in interfaceCollection<E>
- Overrides:
removeAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be removed from this collection- Returns:
true
if this collection changed as a result of the call- Throws:
NullPointerException
- if this collection contains one or more null elements and the specified collection does not support null elements (optional) or if the specified collection is null- See Also:
-
retainAll
Description copied from class:AbstractCollection
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.- Specified by:
retainAll
in interfaceCollection<E>
- Overrides:
retainAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be retained in this collection- Returns:
true
if this collection changed as a result of the call- Throws:
NullPointerException
- if this collection contains one or more null elements and the specified collection does not permit null elements (optional) or if the specified collection is null- See Also:
-
clear
public void clear()Description copied from class:AbstractQueue
Removes all of the elements from this queue. The queue will be empty after this call returns.This implementation repeatedly invokes
poll
until it returnsnull
.- Specified by:
clear
in interfaceCollection<E>
- Overrides:
clear
in classAbstractQueue<E>
-
forEach
Description copied from interface:Iterable
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEach
in interfaceIterable<E>
- Parameters:
action
- The action to be performed for each element- Throws:
NullPointerException
- if the specified action is null
-