001 package org.apache.qpid.util.concurrent;
002 /*
003 *
004 * Licensed to the Apache Software Foundation (ASF) under one
005 * or more contributor license agreements. See the NOTICE file
006 * distributed with this work for additional information
007 * regarding copyright ownership. The ASF licenses this file
008 * to you under the Apache License, Version 2.0 (the
009 * "License"); you may not use this file except in compliance
010 * with the License. You may obtain a copy of the License at
011 *
012 * http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing,
015 * software distributed under the License is distributed on an
016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
017 * KIND, either express or implied. See the License for the
018 * specific language governing permissions and limitations
019 * under the License.
020 *
021 */
022
023
024 import java.util.Collection;
025 import java.util.concurrent.BlockingQueue;
026
027 /**
028 * BatchSynchQueue is an abstraction of the classic producer/consumer buffer pattern for thread interaction. In this
029 * pattern threads can deposit data onto a buffer whilst other threads take data from the buffer and perform usefull
030 * work with it. A BatchSynchQueue adds to this the possibility that producers can be blocked until their data is
031 * consumed or until a consumer chooses to release the producer some time after consuming the data from the queue.
032 *
033 * <p>There are a number of possible advantages to using this technique when compared with having the producers
034 * processing their own data:
035 *
036 * <ul>
037 * <li>Data may be deposited asynchronously in the buffer allowing the producers to continue running.</li>
038 * <li>Data may be deposited synchronously in the buffer so that producers wait until their data has been processed
039 * before being allowed to continue.</li>
040 * <li>Variable rates of production/consumption can be smoothed over by the buffer as it provides space in memory to
041 * hold data between production and consumption.</li>
042 * <li>Consumers may be able to batch data as they consume it leading to more efficient consumption over
043 * individual data item consumption where latency associated with the consume operation can be ammortized.
044 * For example, it may be possibly to ammortize the cost of a disk seek over many producers.</li>
045 * <li>Data from seperate threads can be combined together in the buffer, providing a convenient way of spreading work
046 * amongst many workers and gathering the results together again.</li>
047 * <li>Different types of queue can be used to hold the buffer, resulting in different processing orders. For example,
048 * lifo, fifo, priority heap, etc.</li>
049 * </ul>
050 *
051 * <p/>The asynchronous type of producer/consumer buffers is already well supported by the java.util.concurrent package
052 * (in Java 5) and there is also a synchronous queue implementation available there too. This interface extends the
053 * blocking queue with some more methods for controlling a synchronous blocking queue. In particular it adds additional
054 * take methods that can be used to take data from a queue without releasing producers, so that consumers have an
055 * opportunity to confirm correct processing of the data before producers are released. It also adds a put method with
056 * exceptions so that consumers can signal exception cases back to producers where there are errors in the data.
057 *
058 * <p/>This type of queue is usefull in situations where consumers can obtain an efficiency gain by batching data
059 * from many threads but where synchronous handling of that data is neccessary because producers need to know that
060 * their data has been processed before they continue. For example, sending a bundle of messages together, or writing
061 * many records to disk at once, may result in improved performance but the originators of the messages or disk records
062 * need confirmation that their data has really been sent or saved to disk.
063 *
064 * <p/>The consumer can put an element back onto the queue or send an error message to the elements producer using the
065 * {@link SynchRecord} interface.
066 *
067 * <p/>The {@link #take()}, {@link #drainTo(java.util.Collection<? super E>)} and
068 * {@link #drainTo(java.util.Collection<? super E>, int)} methods from {@link BlockingQueue} should behave as if they
069 * have been called with unblock set to false. That is they take elements from the queue but leave the producers
070 * blocked. These methods do not return collections of {@link SynchRecord}s so they do not supply an interface through
071 * which errors or re-queuings can be applied. If these methods are used then the consumer must succesfully process
072 * all the records it takes.
073 *
074 * <p/>The {@link #put} method should silently swallow any exceptions that consumers attempt to return to the caller.
075 * In order to handle exceptions the {@link #tryPut} method must be used.
076 *
077 * <p/><table id="crc"><caption>CRC Card</caption>
078 * <tr><th> Responsibilities <th> Collaborations
079 * <tr><td> Handle synchronous puts, with possible exceptions.
080 * <tr><td> Allow consumers to take many records from a queue in a batch.
081 * <tr><td> Allow consumers to decide when to unblock synchronous producers.
082 * </table>
083 */
084 public interface BatchSynchQueue<E> extends BlockingQueue<E>
085 {
086 /**
087 * Tries a synchronous put into the queue. If a consumer encounters an exception condition whilst processing the
088 * data that is put, then this is returned to the caller wrapped inside a {@link SynchException}.
089 *
090 * @param e The data element to put into the queue.
091 *
092 * @throws InterruptedException If the thread is interrupted whilst waiting to write to the queue or whilst waiting
093 * on its entry in the queue being consumed.
094 * @throws SynchException If a consumer encounters an error whilst processing the data element.
095 */
096 public void tryPut(E e) throws InterruptedException, SynchException;
097
098 /**
099 * Takes all available data items from the queue or blocks until some become available. The returned items
100 * are wrapped in a {@link SynchRecord} which provides an interface to requeue them or send errors to their
101 * producers, where the producers are still blocked.
102 *
103 * @param c The collection to drain the data items into.
104 * @param unblock If set to <tt>true</tt> the producers for the taken items will be immediately unblocked.
105 *
106 * @return A count of the number of elements that were drained from the queue.
107 */
108 public SynchRef drainTo(Collection<SynchRecord<E>> c, boolean unblock);
109
110 /**
111 * Takes up to maxElements available data items from the queue or blocks until some become available. The returned
112 * items are wrapped in a {@link SynchRecord} which provides an interface to requeue them or send errors to their
113 * producers, where the producers are still blocked.
114 *
115 * @param c The collection to drain the data items into.
116 * @param maxElements The maximum number of elements to drain.
117 * @param unblock If set to <tt>true</tt> the producers for the taken items will be immediately unblocked.
118 *
119 * @return A count of the number of elements that were drained from the queue.
120 */
121 public SynchRef drainTo(Collection<SynchRecord<E>> c, int maxElements, boolean unblock);
122 }
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