11 |
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* A {@link BlockingQueue} in which producers may wait for consumers |
12 |
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* to receive elements. A {@code TransferQueue} may be useful for |
13 |
|
* example in message passing applications in which producers |
14 |
< |
* sometimes (using method {@code transfer}) await receipt of |
15 |
< |
* elements by consumers invoking {@code take} or {@code poll}, |
16 |
< |
* while at other times enqueue elements (via method {@code put}) |
17 |
< |
* without waiting for receipt. Non-blocking and time-out versions of |
18 |
< |
* {@code tryTransfer} are also available. A TransferQueue may also |
19 |
< |
* be queried via {@code hasWaitingConsumer} whether there are any |
20 |
< |
* threads waiting for items, which is a converse analogy to a |
21 |
< |
* {@code peek} 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. {@linkplain |
18 |
> |
* #tryTransfer(Object) Non-blocking} and {@linkplain |
19 |
> |
* #tryTransfer(Object,long,TimeUnit) time-out} versions of {@code |
20 |
> |
* tryTransfer} are also available. A {@code TransferQueue} may also |
21 |
> |
* be queried, via {@link #hasWaitingConsumer}, whether there are any |
22 |
> |
* threads waiting for items, which is a converse analogy to a {@code |
23 |
> |
* peek} operation. |
24 |
|
* |
25 |
< |
* <p>Like any {@code BlockingQueue}, a {@code TransferQueue} may be |
25 |
> |
* <p>Like other blocking queues, a {@code TransferQueue} may be |
26 |
|
* capacity bounded. If so, an attempted {@code transfer} operation |
27 |
|
* may initially block waiting for available space, and/or |
28 |
|
* subsequently block waiting for reception by a consumer. Note that |
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 {@code false} |
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 {@code true} if the element was transferred, else |
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 {@code take} or {@code poll}. |
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 |
< |
* {@code take} or {@code poll}. |
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 |
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 |
108 |
|
|
109 |
|
/** |
110 |
|
* Returns {@code true} if there is at least one consumer waiting |
111 |
< |
* to dequeue an element via {@code take} or {@code poll}. |
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 |
118 |
|
|
119 |
|
/** |
120 |
|
* Returns an estimate of the number of consumers waiting to |
121 |
< |
* dequeue elements via {@code take} or {@code poll}. 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 |
|
* {@link #hasWaitingConsumer}. |
129 |
|
* |
130 |
< |
* @return the number of consumers waiting to dequeue elements |
130 |
> |
* @return the number of consumers waiting to receive elements |
131 |
|
*/ |
132 |
|
int getWaitingConsumerCount(); |
133 |
|
} |