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删除无用代码
git-svn-id: http://code.alibabatech.com/svn/druid/trunk@288 b9813039-fb51-4c41-a8b9-e21c2acb5095
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wenshao
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/*
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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/*
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*
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*
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*
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*
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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 com.alibaba.druid.util;
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import java.util.concurrent.BlockingQueue;
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import java.util.concurrent.SynchronousQueue;
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import java.util.concurrent.TimeUnit;
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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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}
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