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Java™ Platform Standard Ed. 6 |
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java.lang.Object java.util.AbstractCollection<E> java.util.AbstractQueue<E> java.util.concurrent.SynchronousQueue<E>
E
- the type of elements held in this collectionpublic class SynchronousQueue<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.
Constructor Summary | |
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SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy. |
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SynchronousQueue(boolean fair)
Creates a SynchronousQueue with the specified fairness policy. |
Method Summary | ||
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void |
clear()
Does nothing. |
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boolean |
contains(Object o)
Always returns false. |
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boolean |
containsAll(Collection<?> c)
Returns false unless the given collection is empty. |
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int |
drainTo(Collection<? super E> c)
Removes all available elements from this queue and adds them to the given collection. |
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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. |
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boolean |
isEmpty()
Always returns true. |
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Iterator<E> |
iterator()
Returns an empty iterator in which hasNext always returns false. |
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boolean |
offer(E e)
Inserts the specified element into this queue, if another thread is waiting to receive it. |
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boolean |
offer(E o,
long timeout,
TimeUnit unit)
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it. |
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E |
peek()
Always returns null. |
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E |
poll()
Retrieves and removes the head of this queue, if another thread is currently making an element available. |
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E |
poll(long timeout,
TimeUnit unit)
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it. |
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void |
put(E o)
Adds the specified element to this queue, waiting if necessary for another thread to receive it. |
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int |
remainingCapacity()
Always returns zero. |
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boolean |
remove(Object o)
Always returns false. |
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boolean |
removeAll(Collection<?> c)
Always returns false. |
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boolean |
retainAll(Collection<?> c)
Always returns false. |
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int |
size()
Always returns zero. |
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E |
take()
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it. |
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Object[] |
toArray()
Returns a zero-length array. |
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toArray(T[] a)
Sets the zeroeth element of the specified array to null (if the array has non-zero length) and returns it. |
Methods inherited from class java.util.AbstractQueue |
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add, addAll, element, remove |
Methods inherited from class java.util.AbstractCollection |
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toString |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface java.util.concurrent.BlockingQueue |
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add |
Methods inherited from interface java.util.Queue |
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element, remove |
Methods inherited from interface java.util.Collection |
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addAll, equals, hashCode |
Constructor Detail |
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public SynchronousQueue()
public SynchronousQueue(boolean fair)
fair
- if true, waiting threads contend in FIFO order for
access; otherwise the order is unspecified.Method Detail |
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public void put(E o) throws InterruptedException
put
in interface BlockingQueue<E>
o
- the element to add
InterruptedException
- if interrupted while waiting
NullPointerException
- if the specified element is nullpublic boolean offer(E o, long timeout, TimeUnit unit) throws InterruptedException
offer
in interface BlockingQueue<E>
o
- the element to addtimeout
- how long to wait before giving up, in units of
unitunit
- a TimeUnit determining how to interpret the
timeout parameter
InterruptedException
- if interrupted while waiting
NullPointerException
- if the specified element is nullpublic boolean offer(E e)
offer
in interface BlockingQueue<E>
offer
in interface Queue<E>
e
- the element to add
NullPointerException
- if the specified element is nullpublic E take() throws InterruptedException
take
in interface BlockingQueue<E>
InterruptedException
- if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
poll
in interface BlockingQueue<E>
timeout
- how long to wait before giving up, in units of
unitunit
- a TimeUnit determining how to interpret the
timeout parameter
InterruptedException
- if interrupted while waitingpublic E poll()
poll
in interface Queue<E>
public boolean isEmpty()
isEmpty
in interface Collection<E>
isEmpty
in class AbstractCollection<E>
public int size()
size
in interface Collection<E>
size
in class AbstractCollection<E>
public int remainingCapacity()
remainingCapacity
in interface BlockingQueue<E>
public void clear()
clear
in interface Collection<E>
clear
in class AbstractQueue<E>
public boolean contains(Object o)
contains
in interface Collection<E>
contains
in interface BlockingQueue<E>
contains
in class AbstractCollection<E>
o
- the element
public boolean remove(Object o)
remove
in interface Collection<E>
remove
in interface BlockingQueue<E>
remove
in class AbstractCollection<E>
o
- the element to remove
public boolean containsAll(Collection<?> c)
containsAll
in interface Collection<E>
containsAll
in class AbstractCollection<E>
c
- the collection
AbstractCollection.contains(Object)
public boolean removeAll(Collection<?> c)
removeAll
in interface Collection<E>
removeAll
in class AbstractCollection<E>
c
- the collection
AbstractCollection.remove(Object)
,
AbstractCollection.contains(Object)
public boolean retainAll(Collection<?> c)
retainAll
in interface Collection<E>
retainAll
in class AbstractCollection<E>
c
- the collection
AbstractCollection.remove(Object)
,
AbstractCollection.contains(Object)
public E peek()
peek
in interface Queue<E>
public Iterator<E> iterator()
iterator
in interface Iterable<E>
iterator
in interface Collection<E>
iterator
in class AbstractCollection<E>
public Object[] toArray()
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
a
- the array
NullPointerException
- if the specified array is nullpublic int drainTo(Collection<? super E> c)
BlockingQueue
drainTo
in interface BlockingQueue<E>
c
- the collection to transfer elements into
UnsupportedOperationException
- if addition of elements
is not supported by the specified collection
ClassCastException
- if the class of an element of this queue
prevents it from being added to the specified collection
NullPointerException
- if the specified collection is null
IllegalArgumentException
- 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)
BlockingQueue
drainTo
in interface BlockingQueue<E>
c
- the collection to transfer elements intomaxElements
- the maximum number of elements to transfer
UnsupportedOperationException
- if addition of elements
is not supported by the specified collection
ClassCastException
- if the class of an element of this queue
prevents it from being added to the specified collection
NullPointerException
- if the specified collection is null
IllegalArgumentException
- 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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Java™ Platform Standard Ed. 6 |
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