[LANG-762] Handle or document ReflectionToStringBuilder and ToStringBuilder for collections that are not thread safe.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1199773 13f79535-47bb-0310-9956-ffa450edef68

src/test/java/org/apache/commons/lang3/builder/ToStringStyleConcurrencyTest.java

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+/*
+ * 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.
+ */
+
+package org.apache.commons.lang3.builder;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+import org.junit.Test;
+
+/**
+ * Tests concurrent access for the default {@link ToStringStyle}.
+ * <p>
+ * The {@link ToStringStyle} class includes a registry to avoid infinite loops for objects with circular references. We
+ * want to make sure that we do not get concurrency exceptions accessing this registry.
+ * </p>
+ * <p>
+ * This test passes but only tests one aspect of the issue.
+ * </p>
+ * 
+ * @see <a href="https://issues.apache.org/jira/browse/LANG-762">[LANG-762] Handle or document ReflectionToStringBuilder
+ *      and ToStringBuilder for collections that are not thread safe</a>
+ * @since 3.0.2
+ */
+public class ToStringStyleConcurrencyTest {
+
+    static class CollectionHolder<T extends Collection<?>> {
+        T collection;
+
+        CollectionHolder(T collection) {
+            this.collection = collection;
+        }
+    }
+
+    private static final List<Integer> LIST;
+    private static final int LIST_SIZE = 100000;
+    private static final int REPEAT = 100;
+
+    static {
+        LIST = new ArrayList<Integer>(LIST_SIZE);
+        for (int i = 0; i < LIST_SIZE; i++) {
+            LIST.add(Integer.valueOf(i));
+        }
+    }
+
+    @Test
+    public void testLinkedList() throws InterruptedException, ExecutionException {
+        this.testConcurrency(new CollectionHolder<List<Integer>>(new LinkedList<Integer>()));
+    }
+
+    @Test
+    public void testArrayList() throws InterruptedException, ExecutionException {
+        this.testConcurrency(new CollectionHolder<List<Integer>>(new ArrayList<Integer>()));
+    }
+
+    @Test
+    public void testCopyOnWriteArrayList() throws InterruptedException, ExecutionException {
+        this.testConcurrency(new CollectionHolder<List<Integer>>(new CopyOnWriteArrayList<Integer>()));
+    }
+
+    private void testConcurrency(final CollectionHolder<List<Integer>> holder) throws InterruptedException,
+            ExecutionException {
+        final List<Integer> list = holder.collection;
+        // make a big array that takes a long time to toString()
+        list.addAll(LIST);
+        // Create a thread pool with two threads to cause the most contention on the underlying resource.
+        final ExecutorService threadPool = Executors.newFixedThreadPool(2);
+        // Consumes toStrings
+        Callable<Integer> consumer = new Callable<Integer>() {
+            public Integer call() {
+                for (int i = 0; i < REPEAT; i++) {
+                    // Calls ToStringStyle
+                    new ToStringBuilder(holder).append(holder.collection);
+                }
+                return REPEAT;
+            }
+        };
+        Collection<Callable<Integer>> tasks = new ArrayList<Callable<Integer>>();
+        tasks.add(consumer);
+        tasks.add(consumer);
+        final List<Future<Integer>> futures = threadPool.invokeAll(tasks);
+        for (Future<Integer> future : futures) {
+            future.get();
+        }
+    }
+}