/*
 * 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 BlockingQueue in which producers may wait for consumers to receive elements. A TransferQueue may be useful for example in message passing applications in which producers sometimes (using method transfer) await receipt of elements by consumers invoking take or poll, while at other times enqueue elements (via method put) without waiting for receipt. Non-blocking and time-out versions of tryTransfer are also available. A TransferQueue may also be queried via hasWaitingConsumer whether there are any threads waiting for items, which is a converse analogy to a peek operation. 
 Like any BlockingQueue, a TransferQueue may be capacity bounded. If so, an attempted 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 SynchronousQueue, put and transfer are effectively synonymous. 

This interface is a member of the  Java Collections
Framework.
Author:
Doug Lea
Type parameters:
<E> – the type of elements held in this collection
Since:
1.7/**
 * 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.
 *
 * <p>
 * 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.
 *
 * <p>
 * This interface is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @since 1.7
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public interface TransferQueue<E> extends BlockingQueue<E> {
    
Transfers the specified element if there exists a consumer already waiting to receive it, otherwise returning false without enqueuing the element. 
Params:
e – the element to transfer
Throws:
ClassCastException – if the class of the specified element prevents it from being added to this queue
NullPointerException – if the specified element is null
IllegalArgumentException – if some property of the specified element prevents it from being added to this queue
Returns:
true if the element was transferred, else false/**
     * 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 take or poll. 
Params:
e – the element to transfer
Throws:
InterruptedException – if interrupted while waiting, in which case the element is not enqueued.
ClassCastException – if the class of the specified element prevents it from being added to this queue
NullPointerException – if the specified element is null
IllegalArgumentException – if some property of the specified element prevents it from being added to this queue/**
     * 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 take or poll. 
Params:
e – the element to transfer
timeout – how long to wait before giving up, in units of unit
unit – a TimeUnit determining how to interpret the timeout parameter
Throws:
InterruptedException – if interrupted while waiting, in which case the element is not enqueued.
ClassCastException – if the class of the specified element prevents it from being added to this queue
NullPointerException – if the specified element is null
IllegalArgumentException – if some property of the specified element prevents it from being added to this queue
Returns:
true if successful, or false if the specified waiting time elapses before completion, in which case the element is not enqueued./**
     * 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 true if there is at least one consumer waiting to dequeue an element via take or poll. The return value represents a momentary state of affairs. 
Returns:
true if there is at least one waiting consumer/**
     * 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 take or 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 hasWaitingConsumer. 
Returns:
the number of consumers waiting to dequeue elements/**
     * 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();
}