| java.lang.Object | |||
| ↳ | java.util.AbstractCollection<E> | ||
| ↳ | java.util.AbstractQueue<E> | ||
| ↳ | java.util.concurrent.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.
| Public Constructors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Creates a
SynchronousQueue with nonfair access policy.
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Creates a
SynchronousQueue with the specified fairness policy.
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| Public Methods | |||||||||||
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Does nothing.
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Always returns
false.
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Returns
false unless the given collection is empty.
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Removes at most the given number of available elements from
this queue and adds them to the given collection.
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Removes all available elements from this queue and adds them
to the given collection.
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Always returns
true.
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Returns an empty iterator in which
hasNext always returns
false.
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Inserts the specified element into this queue, if another thread is
waiting to receive it.
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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.
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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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Adds the specified element to this queue, waiting if necessary for
another thread to receive it.
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Always returns zero.
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Always returns
false.
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Always returns
false.
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Always returns
false.
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Always returns zero.
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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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Sets the zeroth element of the specified array to
null
(if the array has non-zero length) and returns it.
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Returns a zero-length array.
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[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.util.AbstractQueue
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|
From class
java.util.AbstractCollection
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From class
java.lang.Object
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From interface
java.util.Queue
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From interface
java.util.Collection
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From interface
java.util.concurrent.BlockingQueue
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From interface
java.lang.Iterable
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Creates a SynchronousQueue with nonfair access policy.
Creates a SynchronousQueue with the specified fairness policy.
| fair | if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified. |
|---|
Does nothing.
A SynchronousQueue has no internal capacity.
Always returns false.
A SynchronousQueue has no internal capacity.
| o | the element |
|---|
Developers
false
Returns false unless the given collection is empty.
A SynchronousQueue has no internal capacity.
| c | the collection |
|---|
false unless given collection is empty
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.
| c | the collection to transfer elements into |
|---|---|
| maxElements | the maximum number of elements to transfer |
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.
| c | the collection to transfer elements into |
|---|
Always returns true.
A SynchronousQueue has no internal capacity.
true
Returns an empty iterator in which hasNext always returns
false.
Inserts the specified element into this queue, if another thread is waiting to receive it.
| e | the element to add |
|---|
true if the element was added to this queue, else
false| NullPointerException | if the specified element is null |
|---|
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.
| 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 |
true if successful, or false if the
specified waiting time elapses before a consumer appearsAlways returns null.
A SynchronousQueue does not return elements
unless actively waited on.
null
Retrieves and removes the head of this queue, if another thread is currently making an element available.
null if no
element is available
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.
| timeout | how long to wait before giving up, in units of
unit |
|---|---|
| unit | a TimeUnit determining how to interpret the
timeout parameter |
null if the
specified waiting time elapses before an element is present| InterruptedException |
|---|
Adds the specified element to this queue, waiting if necessary for another thread to receive it.
| e | the element to add |
|---|
Always returns zero.
A SynchronousQueue has no internal capacity.
Always returns false.
A SynchronousQueue has no internal capacity.
| o | the element to remove |
|---|
false
Always returns false.
A SynchronousQueue has no internal capacity.
| c | the collection |
|---|
false
Always returns false.
A SynchronousQueue has no internal capacity.
| c | the collection |
|---|
false
Always returns zero.
A SynchronousQueue has no internal capacity.
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.
| InterruptedException |
|---|
Sets the zeroth element of the specified array to null
(if the array has non-zero length) and returns it.
| a | the array |
|---|
| NullPointerException | if the specified array is null |
|---|
Returns a zero-length array.