| 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 org.springframework.batch.repeat.RepeatException; |
| 20 | |
| 21 | /** |
| 22 | * Abstract implementation that can be extended for both Backport Concurrent and |
| 23 | * JDK 5 Concurrent. |
| 24 | * |
| 25 | * @author Ben Hale |
| 26 | * @author Dave Syer |
| 27 | */ |
| 28 | abstract class AbstractResultQueue extends RepeatInternalStateSupport implements ResultQueue { |
| 29 | |
| 30 | // Arbitrary lock object. |
| 31 | private final Object lock = new Object(); |
| 32 | |
| 33 | // Counter to monitor the difference between expected and actually collected |
| 34 | // results. When this reaches zero there are really no more results. |
| 35 | private volatile int count = 0; |
| 36 | |
| 37 | public boolean isExpecting() { |
| 38 | synchronized (lock) { |
| 39 | // Base the decision about whether we expect more results on a |
| 40 | // counter of the number of expected results actually collected. |
| 41 | return count > 0; |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | public void expect() { |
| 46 | try { |
| 47 | synchronized (lock) { |
| 48 | aquireWait(); |
| 49 | count++; |
| 50 | } |
| 51 | } |
| 52 | catch (InterruptedException e) { |
| 53 | Thread.currentThread().interrupt(); |
| 54 | throw new RepeatException("InterruptedException waiting for to acquire lock on input."); |
| 55 | } |
| 56 | } |
| 57 | |
| 58 | public void put(ResultHolder holder) { |
| 59 | // There should be no need to block here, or to use offer() |
| 60 | addResult(holder); |
| 61 | // Take from the waits queue now to allow another result to |
| 62 | // accumulate. But don't decrement the counter. |
| 63 | releaseWait(); |
| 64 | } |
| 65 | |
| 66 | public ResultHolder take() { |
| 67 | ResultHolder value; |
| 68 | try { |
| 69 | synchronized (lock) { |
| 70 | value = takeResult(); |
| 71 | // Decrement the counter only when the result is collected. |
| 72 | count--; |
| 73 | } |
| 74 | } |
| 75 | catch (InterruptedException e) { |
| 76 | Thread.currentThread().interrupt(); |
| 77 | throw new RepeatException("InterruptedException while waiting for result."); |
| 78 | } |
| 79 | return value; |
| 80 | } |
| 81 | |
| 82 | /** |
| 83 | * Acquire permission for one more task on the queue. |
| 84 | * |
| 85 | * @throws InterruptedException |
| 86 | */ |
| 87 | protected abstract void aquireWait() throws InterruptedException; |
| 88 | |
| 89 | /** |
| 90 | * Release the permit that we were holding while a task was processed. |
| 91 | */ |
| 92 | protected abstract void releaseWait(); |
| 93 | |
| 94 | /** |
| 95 | * Add a {@link ResultHolder} with a finished result to the queue for |
| 96 | * collection. Should not block. May throw an exception to signal that the |
| 97 | * queue is full, but that would be an unexpected condition. |
| 98 | * |
| 99 | * @param resultHolder a {@link ResultHolder} |
| 100 | */ |
| 101 | protected abstract void addResult(ResultHolder resultHolder); |
| 102 | |
| 103 | /** |
| 104 | * Obtain a result from the queue, blocking until one becomes available. |
| 105 | * |
| 106 | * @return a {@link ResultHolder} with the completed result |
| 107 | * @throws InterruptedException if an interrupt is signalled |
| 108 | */ |
| 109 | protected abstract ResultHolder takeResult() throws InterruptedException; |
| 110 | |
| 111 | } |