| 9 |
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|
| 10 |
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/** |
| 11 |
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* A {@link BlockingQueue} in which producers may wait for consumers |
| 12 |
< |
* to receive elements. A <tt>TransferQueue</tt> may be useful for |
| 12 |
> |
* to receive elements. A {@code TransferQueue} may be useful for |
| 13 |
|
* example in message passing applications in which producers |
| 14 |
< |
* sometimes (using method <tt>transfer</tt>) await receipt of |
| 15 |
< |
* elements by consumers invoking <tt>take</tt> or <tt>poll</tt>, |
| 16 |
< |
* while at other times enqueue elements (via method <tt>put</tt>) |
| 17 |
< |
* without waiting for receipt. Non-blocking and time-out versions of |
| 18 |
< |
* <tt>tryTransfer</tt> are also available. A TransferQueue may also |
| 19 |
< |
* be queried via <tt>hasWaitingConsumer</tt> whether there are any |
| 20 |
< |
* threads waiting for items, which is a converse analogy to a |
| 21 |
< |
* <tt>peek</tt> operation |
| 14 |
> |
* sometimes (using method {@link #transfer}) await receipt of |
| 15 |
> |
* elements by consumers invoking {@code take} or {@code poll}, while |
| 16 |
> |
* at other times enqueue elements (via method {@code put}) without |
| 17 |
> |
* waiting for receipt. |
| 18 |
> |
* {@linkplain #tryTransfer(Object) Non-blocking} and |
| 19 |
> |
* {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of |
| 20 |
> |
* {@code tryTransfer} are also available. |
| 21 |
> |
* A {@code TransferQueue} may also be queried, via {@link |
| 22 |
> |
* #hasWaitingConsumer}, whether there are any threads waiting for |
| 23 |
> |
* items, which is a converse analogy to a {@code peek} operation. |
| 24 |
|
* |
| 25 |
< |
* <p>Like any <tt>BlockingQueue</tt>, a <tt>TransferQueue</tt> may be |
| 26 |
< |
* capacity bounded. If so, an attempted <tt>transfer</tt> operation |
| 27 |
< |
* may initially block waiting for available space, and/or |
| 28 |
< |
* subsequently block waiting for reception by a consumer. Note that |
| 29 |
< |
* in a queue with zero capacity, such as {@link SynchronousQueue}, |
| 30 |
< |
* <tt>put</tt> and <tt>transfer</tt> are effectively synonymous. |
| 25 |
> |
* <p>Like other blocking queues, a {@code TransferQueue} may be |
| 26 |
> |
* capacity bounded. If so, an attempted transfer operation may |
| 27 |
> |
* initially block waiting for available space, and/or subsequently |
| 28 |
> |
* block waiting for reception by a consumer. Note that in a queue |
| 29 |
> |
* with zero capacity, such as {@link SynchronousQueue}, {@code put} |
| 30 |
> |
* and {@code transfer} are effectively synonymous. |
| 31 |
|
* |
| 32 |
|
* <p>This interface is a member of the |
| 33 |
|
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 39 |
|
*/ |
| 40 |
|
public interface TransferQueue<E> extends BlockingQueue<E> { |
| 41 |
|
/** |
| 42 |
< |
* Transfers the specified element if there exists a consumer |
| 43 |
< |
* already waiting to receive it, otherwise returning <tt>false</tt> |
| 44 |
< |
* without enqueuing the element. |
| 42 |
> |
* Transfers the element to a waiting consumer immediately, if possible. |
| 43 |
> |
* |
| 44 |
> |
* <p>More precisely, transfers the specified element immediately |
| 45 |
> |
* if there exists a consumer already waiting to receive it (in |
| 46 |
> |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
| 47 |
> |
* otherwise returning {@code false} without enqueuing the element. |
| 48 |
|
* |
| 49 |
|
* @param e the element to transfer |
| 50 |
< |
* @return <tt>true</tt> if the element was transferred, else |
| 51 |
< |
* <tt>false</tt> |
| 50 |
> |
* @return {@code true} if the element was transferred, else |
| 51 |
> |
* {@code false} |
| 52 |
|
* @throws ClassCastException if the class of the specified element |
| 53 |
|
* prevents it from being added to this queue |
| 54 |
|
* @throws NullPointerException if the specified element is null |
| 58 |
|
boolean tryTransfer(E e); |
| 59 |
|
|
| 60 |
|
/** |
| 61 |
< |
* Inserts the specified element into this queue, waiting if |
| 62 |
< |
* necessary for space to become available and the element to be |
| 63 |
< |
* dequeued by a consumer invoking <tt>take</tt> or <tt>poll</tt>. |
| 61 |
> |
* Transfers the element to a consumer, waiting if necessary to do so. |
| 62 |
> |
* |
| 63 |
> |
* <p>More precisely, transfers the specified element immediately |
| 64 |
> |
* if there exists a consumer already waiting to receive it (in |
| 65 |
> |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
| 66 |
> |
* else waits until the element is received by a consumer. |
| 67 |
|
* |
| 68 |
|
* @param e the element to transfer |
| 69 |
|
* @throws InterruptedException if interrupted while waiting, |
| 70 |
< |
* in which case the element is not enqueued. |
| 70 |
> |
* in which case the element is not left enqueued |
| 71 |
|
* @throws ClassCastException if the class of the specified element |
| 72 |
|
* prevents it from being added to this queue |
| 73 |
|
* @throws NullPointerException if the specified element is null |
| 77 |
|
void transfer(E e) throws InterruptedException; |
| 78 |
|
|
| 79 |
|
/** |
| 80 |
< |
* Inserts the specified element into this queue, waiting up to |
| 81 |
< |
* the specified wait time if necessary for space to become |
| 82 |
< |
* available and the element to be dequeued by a consumer invoking |
| 83 |
< |
* <tt>take</tt> or <tt>poll</tt>. |
| 80 |
> |
* Transfers the element to a consumer if it is possible to do so |
| 81 |
> |
* before the timeout elapses. |
| 82 |
> |
* |
| 83 |
> |
* <p>More precisely, transfers the specified element immediately |
| 84 |
> |
* if there exists a consumer already waiting to receive it (in |
| 85 |
> |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
| 86 |
> |
* else waits until the element is received by a consumer, |
| 87 |
> |
* returning {@code false} if the specified wait time elapses |
| 88 |
> |
* before the element can be transferred. |
| 89 |
|
* |
| 90 |
|
* @param e the element to transfer |
| 91 |
|
* @param timeout how long to wait before giving up, in units of |
| 92 |
< |
* <tt>unit</tt> |
| 93 |
< |
* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| 94 |
< |
* <tt>timeout</tt> parameter |
| 95 |
< |
* @return <tt>true</tt> if successful, or <tt>false</tt> if |
| 92 |
> |
* {@code unit} |
| 93 |
> |
* @param unit a {@code TimeUnit} determining how to interpret the |
| 94 |
> |
* {@code timeout} parameter |
| 95 |
> |
* @return {@code true} if successful, or {@code false} if |
| 96 |
|
* the specified waiting time elapses before completion, |
| 97 |
< |
* in which case the element is not enqueued. |
| 97 |
> |
* in which case the element is not left enqueued |
| 98 |
|
* @throws InterruptedException if interrupted while waiting, |
| 99 |
< |
* in which case the element is not enqueued. |
| 99 |
> |
* in which case the element is not left enqueued |
| 100 |
|
* @throws ClassCastException if the class of the specified element |
| 101 |
|
* prevents it from being added to this queue |
| 102 |
|
* @throws NullPointerException if the specified element is null |
| 103 |
|
* @throws IllegalArgumentException if some property of the specified |
| 104 |
|
* element prevents it from being added to this queue |
| 105 |
|
*/ |
| 106 |
< |
boolean tryTransfer(E e, long timeout, TimeUnit unit) |
| 106 |
> |
boolean tryTransfer(E e, long timeout, TimeUnit unit) |
| 107 |
|
throws InterruptedException; |
| 108 |
|
|
| 109 |
|
/** |
| 110 |
< |
* Returns true if there is at least one consumer waiting to |
| 111 |
< |
* dequeue an element via <tt>take</tt> or <tt>poll</tt>. The |
| 112 |
< |
* return value represents a momentary state of affairs. |
| 113 |
< |
* @return true if there is at least one waiting consumer. |
| 110 |
> |
* Returns {@code true} if there is at least one consumer waiting |
| 111 |
> |
* to receive an element via {@link #take} or |
| 112 |
> |
* timed {@link #poll(long,TimeUnit) poll}. |
| 113 |
> |
* The return value represents a momentary state of affairs. |
| 114 |
> |
* |
| 115 |
> |
* @return {@code true} if there is at least one waiting consumer |
| 116 |
|
*/ |
| 117 |
|
boolean hasWaitingConsumer(); |
| 118 |
|
|
| 104 |
– |
|
| 119 |
|
/** |
| 120 |
|
* Returns an estimate of the number of consumers waiting to |
| 121 |
< |
* dequeue elements via <tt>take</tt> or <tt>poll</tt>. The return |
| 122 |
< |
* value is an approximation of a momentary state of affairs, that |
| 123 |
< |
* may be inaccurate if consumers have completed or given up |
| 124 |
< |
* waiting. The value may be useful for monitoring and heuristics, |
| 125 |
< |
* but not for synchronization control. Implementations of this |
| 121 |
> |
* receive elements via {@link #take} or timed |
| 122 |
> |
* {@link #poll(long,TimeUnit) poll}. The return value is an |
| 123 |
> |
* approximation of a momentary state of affairs, that may be |
| 124 |
> |
* inaccurate if consumers have completed or given up waiting. |
| 125 |
> |
* The value may be useful for monitoring and heuristics, but |
| 126 |
> |
* not for synchronization control. Implementations of this |
| 127 |
|
* method are likely to be noticeably slower than those for |
| 128 |
< |
* <tt>hasWaitingConsumer</tt>. |
| 129 |
< |
* @return the number of consumers waiting to dequeue elements |
| 128 |
> |
* {@link #hasWaitingConsumer}. |
| 129 |
> |
* |
| 130 |
> |
* @return the number of consumers waiting to receive elements |
| 131 |
|
*/ |
| 132 |
|
int getWaitingConsumerCount(); |
| 133 |
|
} |
