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Class SynchronousQueue<E>
java.util.concurrent.SynchronousQueue<E>
Type Parameters:
E - the type of elements held in this queue
All Implemented Interfaces:
public 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.
Since:
1.5
Author:
Doug Lea and Bill Scherer and Michael Scott
See Also:
Constructor Summary |
Creates a SynchronousQueue with nonfair access policy.
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Creates a SynchronousQueue with the specified fairness policy.
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Method Summary |
void |
Does nothing.
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boolean |
Always returns false.
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boolean |
Returns false unless the given collection is empty.
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int |
Removes all available elements from this queue and adds them
to the given collection.
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int |
Removes at most the given number of available elements from
this queue and adds them to the given collection.
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boolean |
Always returns true.
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Returns an empty iterator in which hasNext always returns
false.
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boolean |
Inserts the specified element into this queue, if another thread is
waiting to receive it.
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boolean |
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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Always returns null.
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Retrieves and removes the head of this queue, if another thread
is currently making an element available.
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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 |
Adds the specified element to this queue, waiting if necessary for
another thread to receive it.
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int |
Always returns zero.
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boolean |
Always returns false.
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boolean |
Always returns false.
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boolean |
Always returns false.
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int |
Always returns zero.
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Returns an empty spliterator in which calls to
trySplit always return null.
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Retrieves and removes the head of this queue, waiting if necessary
for another thread to insert it.
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Returns a zero-length array.
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Sets the zeroth element of the specified array to null
(if the array has non-zero length) and returns it.
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Always returns "[]".
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Methods inherited from class java.lang. Object |
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Methods inherited from interface java.util. Collection |
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Methods inherited from interface java.lang. Iterable |
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public SynchronousQueue |
() |
Creates a SynchronousQueue with nonfair access policy.
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.
Adds the specified element to this queue, waiting if necessary for
another thread to receive it.
Specified by:
Parameters:
e - the element to add
Throws:
public boolean offer |
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throws |
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Inserts the specified element into this queue, waiting if necessary
up to the specified wait time for another thread to receive it.
Specified by:
Parameters:
e - the element to add
timeout - how long to wait before giving up, in units of
unit
unit - a TimeUnit determining how to interpret the
timeout parameter
Returns:
true if successful, or false if the
specified waiting time elapses before a consumer appears
Throws:
Inserts the specified element into this queue, if another thread is
waiting to receive it.
Specified by:
Parameters:
e - the element to add
Returns:
true if the element was added to this queue, else
false
Throws:
Retrieves and removes the head of this queue, waiting if necessary
for another thread to insert it.
Specified by:
Returns:
the head of this queue
Throws:
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:
Parameters:
timeout - how long to wait before giving up, in units of
unit
unit - a TimeUnit determining how to interpret the
timeout parameter
Returns:
the head of this queue, or null if the
specified waiting time elapses before an element is present
Throws:
Retrieves and removes the head of this queue, if another thread
is currently making an element available.
Specified by:
Returns:
the head of this queue, or null if no
element is available
public boolean isEmpty |
() |
Always returns
true.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Returns:
true
Always returns zero.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Returns:
zero
public int remainingCapacity |
() |
Always returns zero.
A
SynchronousQueue has no internal capacity.
Specified by:
Returns:
zero
Does nothing.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Always returns
false.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Parameters:
o - the element
Returns:
false
Always returns
false.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Parameters:
o - the element to remove
Returns:
false
public boolean containsAll |
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Returns
false unless the given collection is empty.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Parameters:
c - the collection
Returns:
false unless given collection is empty
See Also:
Always returns
false.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Parameters:
c - the collection
Returns:
false
See Also:
Always returns
false.
A
SynchronousQueue has no internal capacity.
Specified by:
Overrides:
Parameters:
c - the collection
Returns:
false
See Also:
Always returns
null.
A
SynchronousQueue does not return elements
unless actively waited on.
Specified by:
Returns:
null
Returns an empty iterator in which
hasNext always returns
false.
Specified by:
Overrides:
Returns:
an empty iterator
Returns an empty spliterator in which calls to
trySplit always return
null.
Specified by:
Returns:
an empty spliterator
Since:
1.8
Returns a zero-length array.
Specified by:
Overrides:
Returns:
a zero-length array
Sets the zeroth element of the specified array to
null
(if the array has non-zero length) and returns it.
Specified by:
Overrides:
Type Parameters:
T - the component type of the array to contain the collection
Parameters:
a - the array
Returns:
the specified array
Throws:
Always returns
"[]".
Overrides:
Returns:
"[]"
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.
Specified by:
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 collection
ClassCastException - if the class of an element of this queue
prevents it from being added to the specified collection
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
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.
Specified by:
Parameters:
c - the collection to transfer elements into
maxElements - 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 collection
ClassCastException - if the class of an element of this queue
prevents it from being added to the specified collection
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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