E - the type of elements held in this collectionpublic class SynchronousQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable
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.
public SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy.
public SynchronousQueue(boolean fair)
Creates a SynchronousQueue with the specified fairness policy.
fair - if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified.public void put(E e)
throws InterruptedException Adds the specified element to this queue, waiting if necessary for another thread to receive it.
put in interface BlockingQueue<E>
e - the element to addInterruptedException - if interrupted while waitingNullPointerException - if the specified element is nullpublic boolean offer(E e,
long timeout,
TimeUnit unit)
throws InterruptedException Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.
offer in interface BlockingQueue<E>
e - the element to addtimeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parametertrue if successful, or false if the specified waiting time elapses before a consumer appearsInterruptedException - if interrupted while waitingNullPointerException - if the specified element is nullpublic boolean offer(E e)
Inserts the specified element into this queue, if another thread is waiting to receive it.
offer in interface BlockingQueue<E>
offer in interface Queue<E>
e - the element to addtrue if the element was added to this queue, else false
NullPointerException - if the specified element is nullpublic E take()
throws InterruptedException Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.
take in interface BlockingQueue<E>
InterruptedException - if interrupted while waitingpublic E poll(long timeout,
TimeUnit unit)
throws InterruptedException Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.
poll in interface BlockingQueue<E>
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameternull if the specified waiting time elapses before an element is presentInterruptedException - if interrupted while waitingpublic E poll()
Retrieves and removes the head of this queue, if another thread is currently making an element available.
poll in interface Queue<E>
null if no element is availablepublic boolean isEmpty()
Always returns true. A SynchronousQueue has no internal capacity.
isEmpty in interface Collection<E>
isEmpty in class AbstractCollection<E>
truepublic int size()
Always returns zero. A SynchronousQueue has no internal capacity.
size in interface Collection<E>
size in class AbstractCollection<E>
public int remainingCapacity()
Always returns zero. A SynchronousQueue has no internal capacity.
remainingCapacity in interface BlockingQueue<E>
public void clear()
Does nothing. A SynchronousQueue has no internal capacity.
clear in interface Collection<E>
clear in class AbstractQueue<E>
public boolean contains(Object o)
Always returns false. A SynchronousQueue has no internal capacity.
contains in interface Collection<E>
contains in interface BlockingQueue<E>
contains in class AbstractCollection<E>
o - the elementfalsepublic boolean remove(Object o)
Always returns false. A SynchronousQueue has no internal capacity.
remove in interface Collection<E>
remove in interface BlockingQueue<E>
remove in class AbstractCollection<E>
o - the element to removefalsepublic boolean containsAll(Collection<?> c)
Returns false unless the given collection is empty. A SynchronousQueue has no internal capacity.
containsAll in interface Collection<E>
containsAll in class AbstractCollection<E>
c - the collectionfalse unless given collection is emptyAbstractCollection.contains(Object)public boolean removeAll(Collection<?> c)
Always returns false. A SynchronousQueue has no internal capacity.
removeAll in interface Collection<E>
removeAll in class AbstractCollection<E>
c - the collectionfalseAbstractCollection.remove(Object), AbstractCollection.contains(Object)
public boolean retainAll(Collection<?> c)
Always returns false. A SynchronousQueue has no internal capacity.
retainAll in interface Collection<E>
retainAll in class AbstractCollection<E>
c - the collectionfalseAbstractCollection.remove(Object), AbstractCollection.contains(Object)
public E peek()
Always returns null. A SynchronousQueue does not return elements unless actively waited on.
public Iterator<E> iterator()
Returns an empty iterator in which hasNext always returns false.
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in class AbstractCollection<E>
public Spliterator<E> spliterator()
Returns an empty spliterator in which calls to Spliterator.trySplit() always return null.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
public Object[] toArray()
Returns a zero-length array.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
Sets the zeroeth element of the specified array to null (if the array has non-zero length) and returns it.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
T - the runtime type of the array to contain the collectiona - the arrayNullPointerException - if the specified array is nullpublic int drainTo(Collection<? super E> c)
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 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.
drainTo in interface BlockingQueue<E>
c - the collection to transfer elements intoUnsupportedOperationException - 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 collectionpublic int drainTo(Collection<? super E> c,
int maxElements) 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 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.
drainTo in interface BlockingQueue<E>
c - the collection to transfer elements intomaxElements - the maximum number of elements to transferUnsupportedOperationException - 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
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