com.google.code.yanf4j.util.TransferQueue Maven / Gradle / Ivy
/*
* Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the
* public domain, as explained at http://creativecommons.org/licenses/publicdomain
*/
package com.google.code.yanf4j.util;
import java.util.concurrent.*;
/**
* A {@link BlockingQueue} in which producers may wait for consumers to receive elements. A
* {@code TransferQueue} may be useful for example in message passing applications in which
* producers sometimes (using method {@code transfer}) await receipt of elements by consumers
* invoking {@code take} or {@code poll}, while at other times enqueue elements (via method
* {@code put}) without waiting for receipt. Non-blocking and time-out versions of
* {@code tryTransfer} are also available. A TransferQueue may also be queried via
* {@code hasWaitingConsumer} whether there are any threads waiting for items, which is a converse
* analogy to a {@code peek} operation.
*
*
* Like any {@code BlockingQueue}, a {@code TransferQueue} may be capacity bounded. If so, an
* attempted {@code transfer} operation may initially block waiting for available space, and/or
* subsequently block waiting for reception by a consumer. Note that in a queue with zero capacity,
* such as {@link SynchronousQueue}, {@code put} and {@code transfer} are effectively synonymous.
*
*
* This interface is a member of the
* Java Collections Framework.
*
* @since 1.7
* @author Doug Lea
* @param the type of elements held in this collection
*/
public interface TransferQueue extends BlockingQueue {
/**
* Transfers the specified element if there exists a consumer already waiting to receive it,
* otherwise returning {@code false} without enqueuing the element.
*
* @param e the element to transfer
* @return {@code true} if the element was transferred, else {@code false}
* @throws ClassCastException if the class of the specified element prevents it from being added
* to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified element prevents it from
* being added to this queue
*/
boolean tryTransfer(E e);
/**
* Inserts the specified element into this queue, waiting if necessary for space to become
* available and the element to be dequeued by a consumer invoking {@code take} or {@code poll}.
*
* @param e the element to transfer
* @throws InterruptedException if interrupted while waiting, in which case the element is not
* enqueued.
* @throws ClassCastException if the class of the specified element prevents it from being added
* to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified element prevents it from
* being added to this queue
*/
void transfer(E e) throws InterruptedException;
/**
* Inserts the specified element into this queue, waiting up to the specified wait time if
* necessary for space to become available and the element to be dequeued by a consumer invoking
* {@code take} or {@code poll}.
*
* @param e the element to transfer
* @param timeout how long to wait before giving up, in units of {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
* @return {@code true} if successful, or {@code false} if the specified waiting time elapses
* before completion, in which case the element is not enqueued.
* @throws InterruptedException if interrupted while waiting, in which case the element is not
* enqueued.
* @throws ClassCastException if the class of the specified element prevents it from being added
* to this queue
* @throws NullPointerException if the specified element is null
* @throws IllegalArgumentException if some property of the specified element prevents it from
* being added to this queue
*/
boolean tryTransfer(E e, long timeout, TimeUnit unit) throws InterruptedException;
/**
* Returns {@code true} if there is at least one consumer waiting to dequeue an element via
* {@code take} or {@code poll}. The return value represents a momentary state of affairs.
*
* @return {@code true} if there is at least one waiting consumer
*/
boolean hasWaitingConsumer();
/**
* Returns an estimate of the number of consumers waiting to dequeue elements via {@code take} or
* {@code poll}. The return value is an approximation of a momentary state of affairs, that may be
* inaccurate if consumers have completed or given up waiting. The value may be useful for
* monitoring and heuristics, but not for synchronization control. Implementations of this method
* are likely to be noticeably slower than those for {@link #hasWaitingConsumer}.
*
* @return the number of consumers waiting to dequeue elements
*/
int getWaitingConsumerCount();
}