java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.SynchronousQueue<E>
- Type Parameters:
E- the type of elements held in this queue
- All Implemented Interfaces:
Serializable,Iterable<E>,Collection<E>,BlockingQueue<E>,Queue<E>
A blocking queue in which each insert
operation must wait for a corresponding remove operation by another
thread, and vice versa. A synchronous queue does not have any
internal capacity, not even a capacity of one. You cannot
peek at a synchronous queue because an element is only
present when you try to remove it; you cannot insert an element
(using any method) unless another thread is trying to remove it;
you cannot iterate as there is nothing to iterate. The
head of the queue is the element that the first queued
inserting thread is trying to add to the queue; if there is no such
queued thread then no element is available for removal and
poll() will return null. For purposes of other
Collection methods (for example contains), a
SynchronousQueue acts as an empty collection. This queue
does not permit null elements.
Synchronous queues are similar to rendezvous channels used in CSP and Ada. They are well suited for handoff designs, in which an object running in one thread must sync up with an object running in another thread in order to hand it some information, event, or task.
This class supports an optional fairness policy for ordering
waiting producer and consumer threads. By default, this ordering
is not guaranteed. However, a queue constructed with fairness set
to true grants threads access in FIFO order.
This class and its iterator implement all of the optional
methods of the Collection and Iterator interfaces.
This class is a member of the Java Collections Framework.
- Since:
- 1.5
- See Also:
-
Constructor Summary
ConstructorsConstructorDescriptionCreates aSynchronousQueuewith nonfair access policy.SynchronousQueue(boolean fair) Creates aSynchronousQueuewith the specified fairness policy. -
Method Summary
Modifier and TypeMethodDescriptionvoidclear()Does nothing.booleanAlways returnsfalse.booleancontainsAll(Collection<?> c) Returnsfalseunless the given collection is empty.intdrainTo(Collection<? super E> c) Removes all available elements from this queue and adds them to the given collection.intdrainTo(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.booleanisEmpty()Always returnstrue.iterator()Returns an empty iterator in whichhasNextalways returnsfalse.booleanInserts the specified element into this queue, if another thread is waiting to receive it.booleanInserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.peek()Always returnsnull.poll()Retrieves and removes the head of this queue, if another thread is currently making an element available.Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.voidAdds the specified element to this queue, waiting if necessary for another thread to receive it.intAlways returns zero.booleanAlways returnsfalse.booleanremoveAll(Collection<?> c) Always returnsfalse.booleanretainAll(Collection<?> c) Always returnsfalse.intsize()Always returns zero.Returns an empty spliterator in which calls totrySplitalways returnnull.take()Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.Object[]toArray()Returns a zero-length array.<T> T[]toArray(T[] a) Sets the zeroth element of the specified array tonull(if the array has non-zero length) and returns it.toString()Always returns"[]".Methods declared in class java.util.AbstractQueue
add, addAll, element, removeMethods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.concurrent.BlockingQueue
addMethods declared in interface java.util.Collection
addAll, equals, hashCode, parallelStream, removeIf, stream, toArray
-
Constructor Details
-
SynchronousQueue
public SynchronousQueue()Creates aSynchronousQueuewith nonfair access policy. -
SynchronousQueue
public SynchronousQueue(boolean fair) Creates aSynchronousQueuewith the specified fairness policy.- Parameters:
fair- if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified.
-
-
Method Details
-
put
Adds the specified element to this queue, waiting if necessary for another thread to receive it.- Specified by:
putin interfaceBlockingQueue<E>- Parameters:
e- the element to add- Throws:
InterruptedException- if interrupted while waitingNullPointerException- if the specified element is null
-
offer
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.- Specified by:
offerin interfaceBlockingQueue<E>- Parameters:
e- the element to addtimeout- how long to wait before giving up, in units ofunitunit- aTimeUnitdetermining how to interpret thetimeoutparameter- Returns:
trueif successful, orfalseif the specified waiting time elapses before a consumer appears- Throws:
InterruptedException- if interrupted while waitingNullPointerException- if the specified element is null
-
offer
Inserts the specified element into this queue, if another thread is waiting to receive it.- Specified by:
offerin interfaceBlockingQueue<E>- Specified by:
offerin interfaceQueue<E>- Parameters:
e- the element to add- Returns:
trueif the element was added to this queue, elsefalse- Throws:
NullPointerException- if the specified element is null
-
take
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.- Specified by:
takein interfaceBlockingQueue<E>- Returns:
- the head of this queue
- Throws:
InterruptedException- if interrupted while waiting
-
poll
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.- Specified by:
pollin interfaceBlockingQueue<E>- Parameters:
timeout- how long to wait before giving up, in units ofunitunit- aTimeUnitdetermining how to interpret thetimeoutparameter- Returns:
- the head of this queue, or
nullif the specified waiting time elapses before an element is present - Throws:
InterruptedException- if interrupted while waiting
-
poll
Retrieves and removes the head of this queue, if another thread is currently making an element available. -
isEmpty
public boolean isEmpty()Always returnstrue. ASynchronousQueuehas no internal capacity.- Specified by:
isEmptyin interfaceCollection<E>- Overrides:
isEmptyin classAbstractCollection<E>- Returns:
true
-
size
public int size()Always returns zero. ASynchronousQueuehas no internal capacity.- Specified by:
sizein interfaceCollection<E>- Returns:
- zero
-
remainingCapacity
public int remainingCapacity()Always returns zero. ASynchronousQueuehas no internal capacity.- Specified by:
remainingCapacityin interfaceBlockingQueue<E>- Returns:
- zero
-
clear
public void clear()Does nothing. ASynchronousQueuehas no internal capacity.- Specified by:
clearin interfaceCollection<E>- Overrides:
clearin classAbstractQueue<E>
-
contains
Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
containsin interfaceBlockingQueue<E>- Specified by:
containsin interfaceCollection<E>- Overrides:
containsin classAbstractCollection<E>- Parameters:
o- the element- Returns:
false
-
remove
Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
removein interfaceBlockingQueue<E>- Specified by:
removein interfaceCollection<E>- Overrides:
removein classAbstractCollection<E>- Parameters:
o- the element to remove- Returns:
false
-
containsAll
Returnsfalseunless the given collection is empty. ASynchronousQueuehas no internal capacity.- Specified by:
containsAllin interfaceCollection<E>- Overrides:
containsAllin classAbstractCollection<E>- Parameters:
c- the collection- Returns:
falseunless given collection is empty- See Also:
-
removeAll
Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
removeAllin interfaceCollection<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- the collection- Returns:
false- See Also:
-
retainAll
Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
retainAllin interfaceCollection<E>- Overrides:
retainAllin classAbstractCollection<E>- Parameters:
c- the collection- Returns:
false- See Also:
-
peek
Always returnsnull. ASynchronousQueuedoes not return elements unless actively waited on. -
iterator
Returns an empty iterator in whichhasNextalways returnsfalse.- Specified by:
iteratorin interfaceCollection<E>- Specified by:
iteratorin interfaceIterable<E>- Specified by:
iteratorin classAbstractCollection<E>- Returns:
- an empty iterator
-
spliterator
Returns an empty spliterator in which calls totrySplitalways returnnull.- Specified by:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Returns:
- an empty spliterator
- Since:
- 1.8
-
toArray
Returns a zero-length array.- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Returns:
- a zero-length array
-
toArray
public <T> T[] toArray(T[] a) Sets the zeroth element of the specified array tonull(if the array has non-zero length) and returns it.- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Type Parameters:
T- the component type of the array to contain the collection- Parameters:
a- the array- Returns:
- the specified array
- Throws:
NullPointerException- if the specified array is null
-
toString
Always returns"[]".- Overrides:
toStringin classAbstractCollection<E>- Returns:
"[]"
-
drainTo
Description copied from interface:BlockingQueueRemoves 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 collectioncmay 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:
drainToin interfaceBlockingQueue<E>- Parameters:
c- the collection to transfer elements into- Returns:
- the number of elements transferred
- Throws:
UnsupportedOperationException- if addition of elements is not supported by the specified collectionClassCastException- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException- 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:BlockingQueueRemoves 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 collectioncmay 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:
drainToin interfaceBlockingQueue<E>- Parameters:
c- the collection to transfer elements intomaxElements- the maximum number of elements to transfer- Returns:
- the number of elements transferred
- Throws:
UnsupportedOperationException- if addition of elements is not supported by the specified collectionClassCastException- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException- 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
-