org.glassfish.grizzly.utils.TransferQueue Maven / Gradle / Ivy
/*
* Copyright (c) 2009, 2020 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
/*
* 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 org.glassfish.grizzly.utils;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
/**
* 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();
}