| 1 | /* |
| 2 | * Copyright 2006-2007 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 | package org.springframework.batch.core.scope.context; |
| 17 | |
| 18 | import java.util.HashMap; |
| 19 | import java.util.Map; |
| 20 | import java.util.Stack; |
| 21 | import java.util.concurrent.atomic.AtomicInteger; |
| 22 | |
| 23 | import org.springframework.batch.core.Step; |
| 24 | import org.springframework.batch.core.StepExecution; |
| 25 | |
| 26 | /** |
| 27 | * Central convenience class for framework use in managing the step scope |
| 28 | * context. Generally only to be used by implementations of {@link Step}. N.B. |
| 29 | * it is the responsibility of every {@link Step} implementation to ensure that |
| 30 | * a {@link StepContext} is available on every thread that might be involved in |
| 31 | * a step execution, including worker threads from a pool. |
| 32 | * |
| 33 | * @author Dave Syer |
| 34 | * |
| 35 | */ |
| 36 | public class StepSynchronizationManager { |
| 37 | |
| 38 | /* |
| 39 | * We have to deal with single and multi-threaded execution, with a single |
| 40 | * and with multiple step execution instances. That's 2x2 = 4 scenarios. |
| 41 | */ |
| 42 | |
| 43 | /** |
| 44 | * Storage for the current step execution; has to be ThreadLocal because it |
| 45 | * is needed to locate a StepContext in components that are not part of a |
| 46 | * Step (like when re-hydrating a scoped proxy). Doesn't use |
| 47 | * InheritableThreadLocal because there are side effects if a step is trying |
| 48 | * to run multiple child steps (e.g. with partitioning). The Stack is used |
| 49 | * to cover the single threaded case, so that the API is the same as |
| 50 | * multi-threaded. |
| 51 | */ |
| 52 | private static final ThreadLocal<Stack<StepExecution>> executionHolder = new ThreadLocal<Stack<StepExecution>>(); |
| 53 | |
| 54 | /** |
| 55 | * Reference counter for each step execution: how many threads are using the |
| 56 | * same one? |
| 57 | */ |
| 58 | private static final Map<StepExecution, AtomicInteger> counts = new HashMap<StepExecution, AtomicInteger>(); |
| 59 | |
| 60 | /** |
| 61 | * Simple map from a running step execution to the associated context. |
| 62 | */ |
| 63 | private static final Map<StepExecution, StepContext> contexts = new HashMap<StepExecution, StepContext>(); |
| 64 | |
| 65 | /** |
| 66 | * Getter for the current context if there is one, otherwise returns null. |
| 67 | * |
| 68 | * @return the current {@link StepContext} or null if there is none (if one |
| 69 | * has not been registered for this thread). |
| 70 | */ |
| 71 | public static StepContext getContext() { |
| 72 | if (getCurrent().isEmpty()) { |
| 73 | return null; |
| 74 | } |
| 75 | synchronized (contexts) { |
| 76 | return contexts.get(getCurrent().peek()); |
| 77 | } |
| 78 | } |
| 79 | |
| 80 | /** |
| 81 | * Register a context with the current thread - always put a matching |
| 82 | * {@link #close()} call in a finally block to ensure that the correct |
| 83 | * context is available in the enclosing block. |
| 84 | * |
| 85 | * @param stepExecution the step context to register |
| 86 | * @return a new {@link StepContext} or the current one if it has the same |
| 87 | * {@link StepExecution} |
| 88 | */ |
| 89 | public static StepContext register(StepExecution stepExecution) { |
| 90 | if (stepExecution == null) { |
| 91 | return null; |
| 92 | } |
| 93 | getCurrent().push(stepExecution); |
| 94 | StepContext context; |
| 95 | synchronized (contexts) { |
| 96 | context = contexts.get(stepExecution); |
| 97 | if (context == null) { |
| 98 | context = new StepContext(stepExecution); |
| 99 | contexts.put(stepExecution, context); |
| 100 | } |
| 101 | } |
| 102 | increment(); |
| 103 | return context; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Method for de-registering the current context - should always and only be |
| 108 | * used by in conjunction with a matching {@link #register(StepExecution)} |
| 109 | * to ensure that {@link #getContext()} always returns the correct value. |
| 110 | * Does not call {@link StepContext#close()} - that is left up to the caller |
| 111 | * because he has a reference to the context (having registered it) and only |
| 112 | * he has knowledge of when the step actually ended. |
| 113 | */ |
| 114 | public static void close() { |
| 115 | StepContext oldSession = getContext(); |
| 116 | if (oldSession == null) { |
| 117 | return; |
| 118 | } |
| 119 | decrement(); |
| 120 | } |
| 121 | |
| 122 | private static void decrement() { |
| 123 | StepExecution current = getCurrent().pop(); |
| 124 | if (current != null) { |
| 125 | int remaining = counts.get(current).decrementAndGet(); |
| 126 | if (remaining <= 0) { |
| 127 | synchronized (contexts) { |
| 128 | contexts.remove(current); |
| 129 | counts.remove(current); |
| 130 | } |
| 131 | } |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | private static void increment() { |
| 136 | StepExecution current = getCurrent().peek(); |
| 137 | if (current != null) { |
| 138 | AtomicInteger count; |
| 139 | synchronized (counts) { |
| 140 | count = counts.get(current); |
| 141 | if (count == null) { |
| 142 | count = new AtomicInteger(); |
| 143 | counts.put(current, count); |
| 144 | } |
| 145 | } |
| 146 | count.incrementAndGet(); |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | private static Stack<StepExecution> getCurrent() { |
| 151 | if (executionHolder.get() == null) { |
| 152 | executionHolder.set(new Stack<StepExecution>()); |
| 153 | } |
| 154 | return executionHolder.get(); |
| 155 | } |
| 156 | |
| 157 | /** |
| 158 | * A convenient "deep" close operation. Call this instead of |
| 159 | * {@link #close()} if the step execution for the current context is ending. |
| 160 | * Delegates to {@link StepContext#close()} and then ensures that |
| 161 | * {@link #close()} is also called in a finally block. |
| 162 | */ |
| 163 | public static void release() { |
| 164 | StepContext context = getContext(); |
| 165 | try { |
| 166 | if (context != null) { |
| 167 | context.close(); |
| 168 | } |
| 169 | } |
| 170 | finally { |
| 171 | close(); |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | } |