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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package java.util.concurrent; |
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/** |
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* A {@link BlockingQueue} in which producers may wait for consumers |
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* to receive elements. A {@code TransferQueue} may be useful for |
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* example in message passing applications in which producers |
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* sometimes (using method {@link #transfer}) await receipt of |
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* elements by consumers invoking {@code take} or {@code poll}, while |
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* at other times enqueue elements (via method {@code put}) without |
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* waiting for receipt. |
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* {@linkplain #tryTransfer(Object) Non-blocking} and |
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* {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of |
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* {@code tryTransfer} are also available. |
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* A {@code TransferQueue} may also be queried, via {@link |
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* #hasWaitingConsumer}, whether there are any threads waiting for |
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* items, which is a converse analogy to a {@code peek} operation. |
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* |
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* <p>Like other blocking queues, a {@code TransferQueue} may be |
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* capacity bounded. If so, an attempted transfer operation may |
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* initially block waiting for available space, and/or subsequently |
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* block waiting for reception by a consumer. Note that in a queue |
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* with zero capacity, such as {@link SynchronousQueue}, {@code put} |
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* and {@code transfer} are effectively synonymous. |
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* |
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* <p>This interface is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this collection |
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*/ |
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public interface TransferQueue<E> extends BlockingQueue<E> { |
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/** |
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* Transfers the element to a waiting consumer immediately, if possible. |
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* |
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* <p>More precisely, transfers the specified element immediately |
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* if there exists a consumer already waiting to receive it (in |
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* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
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* otherwise returning {@code false} without enqueuing the element. |
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* |
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* @param e the element to transfer |
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* @return {@code true} if the element was transferred, else |
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* {@code false} |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this queue |
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* @throws NullPointerException if the specified element is null |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this queue |
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*/ |
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boolean tryTransfer(E e); |
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/** |
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* Transfers the element to a consumer, waiting if necessary to do so. |
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* |
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* <p>More precisely, transfers the specified element immediately |
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* if there exists a consumer already waiting to receive it (in |
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* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
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* else waits until the element is received by a consumer. |
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* |
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* @param e the element to transfer |
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* @throws InterruptedException if interrupted while waiting, |
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* in which case the element is not left enqueued |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this queue |
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* @throws NullPointerException if the specified element is null |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this queue |
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*/ |
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void transfer(E e) throws InterruptedException; |
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/** |
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* Transfers the element to a consumer if it is possible to do so |
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* before the timeout elapses. |
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* |
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* <p>More precisely, transfers the specified element immediately |
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* if there exists a consumer already waiting to receive it (in |
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* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
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* else waits until the element is received by a consumer, |
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* returning {@code false} if the specified wait time elapses |
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* before the element can be transferred. |
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* |
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* @param e the element to transfer |
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* @param timeout how long to wait before giving up, in units of |
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* {@code unit} |
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* @param unit a {@code TimeUnit} determining how to interpret the |
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* {@code timeout} parameter |
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* @return {@code true} if successful, or {@code false} if |
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* the specified waiting time elapses before completion, |
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* in which case the element is not left enqueued |
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* @throws InterruptedException if interrupted while waiting, |
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* in which case the element is not left enqueued |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this queue |
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* @throws NullPointerException if the specified element is null |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this queue |
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*/ |
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boolean tryTransfer(E e, long timeout, TimeUnit unit) |
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throws InterruptedException; |
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/** |
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* Returns {@code true} if there is at least one consumer waiting |
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* to receive an element via {@link #take} or |
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* timed {@link #poll(long,TimeUnit) poll}. |
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* The return value represents a momentary state of affairs. |
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* |
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* @return {@code true} if there is at least one waiting consumer |
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*/ |
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boolean hasWaitingConsumer(); |
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/** |
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* Returns an estimate of the number of consumers waiting to |
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* receive elements via {@link #take} or timed |
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* {@link #poll(long,TimeUnit) poll}. The return value is an |
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* approximation of a momentary state of affairs, that may be |
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* inaccurate if consumers have completed or given up waiting. |
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* The value may be useful for monitoring and heuristics, but |
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* not for synchronization control. Implementations of this |
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* method are likely to be noticeably slower than those for |
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* {@link #hasWaitingConsumer}. |
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* |
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* @return the number of consumers waiting to receive elements |
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*/ |
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int getWaitingConsumerCount(); |
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} |