1 /*
2 * Copyright 2002-2007 the original author or authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package org.springframework.batch.repeat.support;
18
19 import java.util.NoSuchElementException;
20 import java.util.concurrent.BlockingQueue;
21
22 import org.springframework.core.task.TaskExecutor;
23
24 /**
25 * Abstraction for queue of {@link ResultHolder} objects. Acts a bit likeT a
26 * {@link BlockingQueue} with the ability to count the number of items it
27 * expects to ever hold. When clients schedule an item to be added they call
28 * {@link #expect()}, and then collect the result later with {@link #take()}.
29 * Result providers in another thread call {@link #put(Object)} to notify the
30 * expecting client of a new result.
31 *
32 * @author Dave Syer
33 * @author Ben Hale
34 */
35 interface ResultQueue<T> {
36
37 /**
38 * In a master-slave pattern, the master calls this method paired with
39 * {@link #take()} to manage the flow of items. Normally a task is submitted
40 * for processing in another thread, at which point the master uses this
41 * method to keep track of the number of expected results. It has the
42 * personality of an counter increment, rather than a work queue, which is
43 * usually managed elsewhere, e.g. by a {@link TaskExecutor}.<br/><br/>
44 * Implementations may choose to block here, if they need to limit the
45 * number or rate of tasks being submitted.
46 *
47 * @throws InterruptedException if the call blocks and is then interrupted.
48 */
49 void expect() throws InterruptedException;
50
51 /**
52 * Once it is expecting a result, clients call this method to satisfy the
53 * expectation. In a master-worker pattern, the workers call this method to
54 * deposit the result of a finished task on the queue for collection.
55 *
56 * @param result the result for later collection.
57 *
58 * @throws IllegalArgumentException if the queue is not expecting a new
59 * result
60 */
61 void put(T result) throws IllegalArgumentException;
62
63 /**
64 * Gets the next available result, blocking if there are none yet available.
65 *
66 * @return a result previously deposited
67 *
68 * @throws NoSuchElementException if there is no result expected
69 * @throws InterruptedException if the operation is interrupted while
70 * waiting
71 */
72 T take() throws NoSuchElementException, InterruptedException;
73
74 /**
75 * Used by master thread to verify that there are results available from
76 * {@link #take()} without possibly having to block and wait.
77 *
78 * @return true if there are no results available
79 */
80 boolean isEmpty();
81
82 /**
83 * Check if any results are expected. Usually used by master thread to drain
84 * queue when it is finished.
85 *
86 * @return true if more results are expected, but possibly not yet
87 * available.
88 */
89 public boolean isExpecting();
90
91 }