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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/licenses/publicdomain |
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*/ |
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|
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package jsr166y; |
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import java.util.concurrent.*; |
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|
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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 <tt>TransferQueue</tt> may be useful for |
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* example in message passing applications in which producers |
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* sometimes (using method <tt>transfer</tt>) await receipt of |
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* elements by consumers invoking <tt>take</tt> or <tt>poll</tt>, |
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* while at other times enqueue elements (via method <tt>put</tt>) |
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* without waiting for receipt. Non-blocking and time-out versions of |
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* <tt>tryTransfer</tt> are also available. A TransferQueue may also |
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* be queried via <tt>hasWaitingConsumer</tt> whether there are any |
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* threads waiting for items, which is a converse analogy to a |
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* <tt>peek</tt> operation |
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* |
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* <p>Like any <tt>BlockingQueue</tt>, a <tt>TransferQueue</tt> may be |
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* capacity bounded. If so, an attempted <tt>transfer</tt> operation |
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* may initially block waiting for available space, and/or |
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* subsequently block waiting for reception by a consumer. Note that |
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* in a queue with zero capacity, such as {@link SynchronousQueue}, |
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* <tt>put</tt> and <tt>transfer</tt> 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 specified element if there exists a consumer |
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* already waiting to receive it, otherwise returning <tt>false</tt> |
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* without enqueuing the element. |
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* |
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* @param e the element to transfer |
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* @return <tt>true</tt> if the element was transferred, else |
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* <tt>false</tt> |
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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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/** |
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* Inserts the specified element into this queue, waiting if |
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* necessary for space to become available and the element to be |
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* dequeued by a consumer invoking <tt>take</tt> or <tt>poll</tt>. |
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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 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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/** |
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* Inserts the specified element into this queue, waiting up to |
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* the specified wait time if necessary for space to become |
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* available and the element to be dequeued by a consumer invoking |
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* <tt>take</tt> or <tt>poll</tt>. |
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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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* <tt>unit</tt> |
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
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* <tt>timeout</tt> parameter |
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* @return <tt>true</tt> if successful, or <tt>false</tt> if |
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* the specified waiting time elapses before completion, |
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* in which case the element is not enqueued. |
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* @throws InterruptedException if interrupted while waiting, |
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* in which case the element is not 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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/** |
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* Returns true if there is at least one consumer waiting to |
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* dequeue an element via <tt>take</tt> or <tt>poll</tt>. The |
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* return value represents a momentary state of affairs. |
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* @return 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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|
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/** |
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* Returns an estimate of the number of consumers waiting to |
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* dequeue elements via <tt>take</tt> or <tt>poll</tt>. The return |
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* value is an approximation of a momentary state of affairs, that |
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* may be inaccurate if consumers have completed or given up |
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* waiting. The value may be useful for monitoring and heuristics, |
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* but 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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* <tt>hasWaitingConsumer</tt>. |
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* @return the number of consumers waiting to dequeue elements |
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*/ |
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int getWaitingConsumerCount(); |
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} |
