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JavaTM 2 Platform Standard Ed. 5.0 |
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java.lang.Objectjava.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 put must wait for a take, 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 take it; you cannot add 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 thread is trying to add to the queue; if there are no queued threads then no element is being added and the head is 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. Fairness generally decreases throughput but reduces variability and avoids starvation.
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 | |
|---|---|
SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy. |
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SynchronousQueue(boolean fair)
Creates a SynchronousQueue with specified fairness policy. |
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| Method Summary | ||
|---|---|---|
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 given collection is empty. |
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int |
drainTo(Collection<? super E> c)
Removes all available elements from this queue and adds them into 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 into 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 o)
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. |
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| 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 |
|---|
public SynchronousQueue()
public SynchronousQueue(boolean fair)
fair - if true, threads contend in FIFO order for access;
otherwise the order is unspecified.| Method Detail |
|---|
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 null.
public 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 null.
public E take()
throws InterruptedException
take in interface BlockingQueue<E>InterruptedException - if interrupted while waiting.
public 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 waiting.public boolean offer(E o)
offer in interface BlockingQueue<E>offer in interface Queue<E>o - the element to add.
NullPointerException - if the specified element is nullpublic 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 class AbstractCollection<E>o - the element
public boolean remove(Object o)
remove in interface Collection<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
public int drainTo(Collection<? super E> c)
BlockingQueue
drainTo in interface BlockingQueue<E>c - the collection to transfer elements into
public 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
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JavaTM 2 Platform Standard Ed. 5.0 |
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Copyright 2004 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.