1771N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 1771N/A * This code is free software; you can redistribute it and/or modify it 1771N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 1771N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 1771N/A * This code is distributed in the hope that it will be useful, but WITHOUT 1771N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 1771N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 1771N/A * version 2 for more details (a copy is included in the LICENSE file that 1771N/A * You should have received a copy of the GNU General Public License version 1771N/A * 2 along with this work; if not, write to the Free Software Foundation, 1771N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 1771N/A * This file is available under and governed by the GNU General Public 1771N/A * License version 2 only, as published by the Free Software Foundation. 1771N/A * However, the following notice accompanied the original version of this 1771N/A * Written by Doug Lea with assistance from members of JCP JSR-166 1771N/A * Expert Group and released to the public domain, as explained at 1771N/A * A {@link BlockingQueue} in which producers may wait for consumers 1771N/A * to receive elements. A {@code TransferQueue} may be useful for 1771N/A * example in message passing applications in which producers 1771N/A * sometimes (using method {@link #transfer}) await receipt of 1771N/A * elements by consumers invoking {@code take} or {@code poll}, while 1771N/A * at other times enqueue elements (via method {@code put}) without 1771N/A * {@linkplain #tryTransfer(Object) Non-blocking} and 1771N/A * {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of 1771N/A * {@code tryTransfer} are also available. 1771N/A * A {@code TransferQueue} may also be queried, via {@link 1771N/A * #hasWaitingConsumer}, whether there are any threads waiting for 1771N/A * items, which is a converse analogy to a {@code peek} operation. 1771N/A * <p>Like other blocking queues, a {@code TransferQueue} may be 1771N/A * capacity bounded. If so, an attempted transfer operation may 1771N/A * initially block waiting for available space, and/or subsequently 1771N/A * block waiting for reception by a consumer. Note that in a queue 1771N/A * with zero capacity, such as {@link SynchronousQueue}, {@code put} 1771N/A * and {@code transfer} are effectively synonymous. 1771N/A * <p>This interface is a member of the 1771N/A * Java Collections Framework</a>. 1771N/A * @param <E> the type of elements held in this collection 1771N/A * Transfers the element to a waiting consumer immediately, if possible. 1771N/A * <p>More precisely, transfers the specified element immediately 1771N/A * if there exists a consumer already waiting to receive it (in 1771N/A * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), 1771N/A * otherwise returning {@code false} without enqueuing the element. 1771N/A * @param e the element to transfer 1771N/A * @return {@code true} if the element was transferred, else 1771N/A * @throws ClassCastException if the class of the specified element 1771N/A * prevents it from being added to this queue 1771N/A * @throws NullPointerException if the specified element is null 1771N/A * @throws IllegalArgumentException if some property of the specified 1771N/A * element prevents it from being added to this queue 1771N/A * Transfers the element to a consumer, waiting if necessary to do so. 1771N/A * <p>More precisely, transfers the specified element immediately 1771N/A * if there exists a consumer already waiting to receive it (in 1771N/A * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), 1771N/A * else waits until the element is received by a consumer. 1771N/A * @param e the element to transfer 1771N/A * @throws InterruptedException if interrupted while waiting, 1771N/A * in which case the element is not left enqueued 1771N/A * @throws ClassCastException if the class of the specified element 1771N/A * prevents it from being added to this queue 1771N/A * @throws NullPointerException if the specified element is null 1771N/A * @throws IllegalArgumentException if some property of the specified 1771N/A * element prevents it from being added to this queue 1771N/A * Transfers the element to a consumer if it is possible to do so 1771N/A * before the timeout elapses. 1771N/A * <p>More precisely, transfers the specified element immediately 1771N/A * if there exists a consumer already waiting to receive it (in 1771N/A * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), 1771N/A * else waits until the element is received by a consumer, 1771N/A * returning {@code false} if the specified wait time elapses 1771N/A * before the element can be transferred. 1771N/A * @param e the element to transfer 1771N/A * @param timeout how long to wait before giving up, in units of 1771N/A * @param unit a {@code TimeUnit} determining how to interpret the 1771N/A * {@code timeout} parameter 1771N/A * @return {@code true} if successful, or {@code false} if 1771N/A * the specified waiting time elapses before completion, 1771N/A * in which case the element is not left enqueued 1771N/A * @throws InterruptedException if interrupted while waiting, 1771N/A * in which case the element is not left enqueued 1771N/A * @throws ClassCastException if the class of the specified element 1771N/A * prevents it from being added to this queue 1771N/A * @throws NullPointerException if the specified element is null 1771N/A * @throws IllegalArgumentException if some property of the specified 1771N/A * element prevents it from being added to this queue 1771N/A * Returns {@code true} if there is at least one consumer waiting 1771N/A * to receive an element via {@link #take} or 1771N/A * timed {@link #poll(long,TimeUnit) poll}. 1771N/A * The return value represents a momentary state of affairs. 1771N/A * @return {@code true} if there is at least one waiting consumer 1771N/A * Returns an estimate of the number of consumers waiting to 1771N/A * receive elements via {@link #take} or timed 1771N/A * {@link #poll(long,TimeUnit) poll}. The return value is an 1771N/A * approximation of a momentary state of affairs, that may be 1771N/A * inaccurate if consumers have completed or given up waiting. 1771N/A * The value may be useful for monitoring and heuristics, but 1771N/A * not for synchronization control. Implementations of this 1771N/A * method are likely to be noticeably slower than those for 1771N/A * {@link #hasWaitingConsumer}. 1771N/A * @return the number of consumers waiting to receive elements