| package org.apache.qpid.util.concurrent; |
| /* |
| * |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| * |
| */ |
| |
| |
| import java.util.Collection; |
| import java.util.concurrent.BlockingQueue; |
| |
| /** |
| * BatchSynchQueue is an abstraction of the classic producer/consumer buffer pattern for thread interaction. In this |
| * pattern threads can deposit data onto a buffer whilst other threads take data from the buffer and perform usefull |
| * work with it. A BatchSynchQueue adds to this the possibility that producers can be blocked until their data is |
| * consumed or until a consumer chooses to release the producer some time after consuming the data from the queue. |
| * |
| * <p>There are a number of possible advantages to using this technique when compared with having the producers |
| * processing their own data: |
| * |
| * <ul> |
| * <li>Data may be deposited asynchronously in the buffer allowing the producers to continue running.</li> |
| * <li>Data may be deposited synchronously in the buffer so that producers wait until their data has been processed |
| * before being allowed to continue.</li> |
| * <li>Variable rates of production/consumption can be smoothed over by the buffer as it provides space in memory to |
| * hold data between production and consumption.</li> |
| * <li>Consumers may be able to batch data as they consume it leading to more efficient consumption over |
| * individual data item consumption where latency associated with the consume operation can be ammortized. |
| * For example, it may be possibly to ammortize the cost of a disk seek over many producers.</li> |
| * <li>Data from seperate threads can be combined together in the buffer, providing a convenient way of spreading work |
| * amongst many workers and gathering the results together again.</li> |
| * <li>Different types of queue can be used to hold the buffer, resulting in different processing orders. For example, |
| * lifo, fifo, priority heap, etc.</li> |
| * </ul> |
| * |
| * <p/>The asynchronous type of producer/consumer buffers is already well supported by the java.util.concurrent package |
| * (in Java 5) and there is also a synchronous queue implementation available there too. This interface extends the |
| * blocking queue with some more methods for controlling a synchronous blocking queue. In particular it adds additional |
| * take methods that can be used to take data from a queue without releasing producers, so that consumers have an |
| * opportunity to confirm correct processing of the data before producers are released. It also adds a put method with |
| * exceptions so that consumers can signal exception cases back to producers where there are errors in the data. |
| * |
| * <p/>This type of queue is usefull in situations where consumers can obtain an efficiency gain by batching data |
| * from many threads but where synchronous handling of that data is neccessary because producers need to know that |
| * their data has been processed before they continue. For example, sending a bundle of messages together, or writing |
| * many records to disk at once, may result in improved performance but the originators of the messages or disk records |
| * need confirmation that their data has really been sent or saved to disk. |
| * |
| * <p/>The consumer can put an element back onto the queue or send an error message to the elements producer using the |
| * {@link SynchRecord} interface. |
| * |
| * <p/>The {@link #take()}, {@link #drainTo(java.util.Collection<? super E>)} and |
| * {@link #drainTo(java.util.Collection<? super E>, int)} methods from {@link BlockingQueue} should behave as if they |
| * have been called with unblock set to false. That is they take elements from the queue but leave the producers |
| * blocked. These methods do not return collections of {@link SynchRecord}s so they do not supply an interface through |
| * which errors or re-queuings can be applied. If these methods are used then the consumer must succesfully process |
| * all the records it takes. |
| * |
| * <p/>The {@link #put} method should silently swallow any exceptions that consumers attempt to return to the caller. |
| * In order to handle exceptions the {@link #tryPut} method must be used. |
| * |
| * <p/><table id="crc"><caption>CRC Card</caption> |
| * <tr><th> Responsibilities <th> Collaborations |
| * <tr><td> Handle synchronous puts, with possible exceptions. |
| * <tr><td> Allow consumers to take many records from a queue in a batch. |
| * <tr><td> Allow consumers to decide when to unblock synchronous producers. |
| * </table> |
| */ |
| public interface BatchSynchQueue<E> extends BlockingQueue<E> |
| { |
| /** |
| * Tries a synchronous put into the queue. If a consumer encounters an exception condition whilst processing the |
| * data that is put, then this is returned to the caller wrapped inside a {@link SynchException}. |
| * |
| * @param e The data element to put into the queue. |
| * |
| * @throws InterruptedException If the thread is interrupted whilst waiting to write to the queue or whilst waiting |
| * on its entry in the queue being consumed. |
| * @throws SynchException If a consumer encounters an error whilst processing the data element. |
| */ |
| public void tryPut(E e) throws InterruptedException, SynchException; |
| |
| /** |
| * Takes all available data items from the queue or blocks until some become available. The returned items |
| * are wrapped in a {@link SynchRecord} which provides an interface to requeue them or send errors to their |
| * producers, where the producers are still blocked. |
| * |
| * @param c The collection to drain the data items into. |
| * @param unblock If set to <tt>true</tt> the producers for the taken items will be immediately unblocked. |
| * |
| * @return A count of the number of elements that were drained from the queue. |
| */ |
| public SynchRef drainTo(Collection<SynchRecord<E>> c, boolean unblock); |
| |
| /** |
| * Takes up to maxElements available data items from the queue or blocks until some become available. The returned |
| * items are wrapped in a {@link SynchRecord} which provides an interface to requeue them or send errors to their |
| * producers, where the producers are still blocked. |
| * |
| * @param c The collection to drain the data items into. |
| * @param maxElements The maximum number of elements to drain. |
| * @param unblock If set to <tt>true</tt> the producers for the taken items will be immediately unblocked. |
| * |
| * @return A count of the number of elements that were drained from the queue. |
| */ |
| public SynchRef drainTo(Collection<SynchRecord<E>> c, int maxElements, boolean unblock); |
| } |