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java.util.concurrent
class SynchronousQueue

java.lang.Object extended by java.util.AbstractCollection extended by java.util.AbstractQueue extended by java.util.concurrent.SynchronousQueue
All Implemented Interfaces:
Serializable, Collection, Queue, BlockingQueue

Most common way to construct:

SynchronousQueue q = new SynchronousQueue();

Based on 113 examples


public class SynchronousQueue
extends AbstractQueue
implements BlockingQueue, Serializable

A {@linkplain BlockingQueue 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 {@link Collection} and {@link Iterator} interfaces.

This class is a member of the Java Collections Framework.


Constructor Summary

          Creates a SynchronousQueue with nonfair access policy.
SynchronousQueue(boolean fair)

          Creates a SynchronousQueue with the specified fairness policy.
 
Method Summary
 void

          Does nothing.
 boolean

          Always returns false.
 boolean

          Returns false unless the given collection is empty.
 int

          
 int
drainTo(Collection c, int maxElements)

          
 boolean

          Always returns true.
 Iterator

          Returns an empty iterator in which hasNext always returns false.
 boolean

          Inserts the specified element into this queue, if another thread is waiting to receive it.
 boolean
offer(Object 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.
 Object

          Always returns null.
 Object

          Retrieves and removes the head of this queue, if another thread is currently making an element available.
 Object
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.
 void

          Adds the specified element to this queue, waiting if necessary for another thread to receive it.
 int

          Always returns zero.
 boolean

          Always returns false.
 boolean

          Always returns false.
 boolean

          Always returns false.
 int

          Always returns zero.
 Object

          Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.
 Object[]

          Returns a zero-length array.
 Object[]

          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
add, addAll, clear, element, remove
 
Methods inherited from class java.util.AbstractCollection
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

SynchronousQueue

public SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy.


SynchronousQueue

public SynchronousQueue(boolean fair)
Creates a SynchronousQueue with the specified fairness policy.

Parameters:
fair - if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified.
Method Detail

clear

public void clear()
Does nothing. A SynchronousQueue has no internal capacity.

Overrides:
clear in class AbstractQueue

contains

public boolean contains(Object o)
Always returns false. A SynchronousQueue has no internal capacity.

Overrides:
contains in class AbstractCollection
Parameters:
o - the element
Returns:
false

containsAll

public boolean containsAll(Collection c)
Returns false unless the given collection is empty. A SynchronousQueue has no internal capacity.

Overrides:
containsAll in class AbstractCollection
Parameters:
c - the collection
Returns:
false unless given collection is empty

drainTo

public int drainTo(Collection c)
Parameters:
c

drainTo

public int drainTo(Collection c,
                   int maxElements)
Parameters:
c
maxElements

isEmpty

public boolean isEmpty()
Always returns true. A SynchronousQueue has no internal capacity.

Overrides:
isEmpty in class AbstractCollection
Returns:
true

iterator

public Iterator iterator()
Returns an empty iterator in which hasNext always returns false.

Overrides:
iterator in class AbstractCollection
Returns:
an empty iterator

offer

public boolean offer(Object e)
Inserts the specified element into this queue, if another thread is waiting to receive it.

Parameters:
e - the element to add
Returns:
true if the element was added to this queue, else false

offer

public boolean offer(Object o,
                     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.

Parameters:
o
timeout
unit
Returns:
true if successful, or false if the specified waiting time elapses before a consumer appears.
Throws:
InterruptedException - {@inheritDoc}

peek

public Object peek()
Always returns null. A SynchronousQueue does not return elements unless actively waited on.

Returns:
null

poll

public Object poll()
Retrieves and removes the head of this queue, if another thread is currently making an element available.

Returns:
the head of this queue, or null if no element is available.

poll

public Object 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.

Parameters:
timeout
unit
Returns:
the head of this queue, or null if the specified waiting time elapses before an element is present.
Throws:
InterruptedException - {@inheritDoc}

put

public void put(Object o)
         throws InterruptedException
Adds the specified element to this queue, waiting if necessary for another thread to receive it.

Parameters:
o
Throws:
InterruptedException - {@inheritDoc}

remainingCapacity

public int remainingCapacity()
Always returns zero. A SynchronousQueue has no internal capacity.

Returns:
zero.

remove

public boolean remove(Object o)
Always returns false. A SynchronousQueue has no internal capacity.

Overrides:
remove in class AbstractCollection
Parameters:
o - the element to remove
Returns:
false

removeAll

public boolean removeAll(Collection c)
Always returns false. A SynchronousQueue has no internal capacity.

Overrides:
removeAll in class AbstractCollection
Parameters:
c - the collection
Returns:
false

retainAll

public boolean retainAll(Collection c)
Always returns false. A SynchronousQueue has no internal capacity.

Overrides:
retainAll in class AbstractCollection
Parameters:
c - the collection
Returns:
false

size

public int size()
Always returns zero. A SynchronousQueue has no internal capacity.

Overrides:
size in class AbstractCollection
Returns:
zero.

take

public Object take()
            throws InterruptedException
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.

Returns:
the head of this queue
Throws:
InterruptedException - {@inheritDoc}

toArray

public Object[] toArray()
Returns a zero-length array.

Overrides:
toArray in class AbstractCollection
Returns:
a zero-length array

toArray

public Object[] toArray(Object[] a)
Sets the zeroeth element of the specified array to null (if the array has non-zero length) and returns it.

Overrides:
toArray in class AbstractCollection
Parameters:
a - the array
Returns:
the specified array


This documentation differs from the official API. Jadeite adds extra features to the API including: variable font sizes, constructions examples, placeholders for classes and methods, and auto-generated “See Also” links. Additionally it is missing some items found in standard Javadoc documentation, including: generics type information, “Deprecated” tags and comments, “See Also” links, along with other minor differences. Please send any questions or feedback to bam@cs.cmu.edu.
This page displays the Jadeite version of the documention, which is derived from the offical documentation that contains this copyright notice:
Copyright 2008 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
The official Sun™ documentation can be found here at http://java.sun.com/javase/6/docs/api/.