Synchronize forEach() in SynchronizedCollection

src/main/java/org/apache/commons/collections4/collection/SynchronizedCollection.java

@@ -20,6 +20,7 @@
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Objects;
+import java.util.function.Consumer;
 import java.util.function.Predicate;
 
 /**
@@ -142,6 +143,16 @@ public boolean equals(final Object object) {
         }
     }
 
+    /**
+     * @since 4.6.0
+     */
+    @Override
+    public void forEach(final Consumer<? super E> action) {
+        synchronized (lock) {
+            decorated().forEach(action);
+        }
+    }
+
     @Override
     public int hashCode() {
         synchronized (lock) {

src/test/java/org/apache/commons/collections4/collection/SynchronizedCollectionTest.java

@@ -16,16 +16,52 @@
  */
 package org.apache.commons.collections4.collection;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.apache.commons.collections4.bag.HashBag;
+import org.apache.commons.collections4.bag.SynchronizedBag;
+import org.apache.commons.collections4.bag.SynchronizedSortedBag;
+import org.apache.commons.collections4.bag.TreeBag;
+import org.apache.commons.collections4.multiset.HashMultiSet;
+import org.apache.commons.collections4.multiset.SynchronizedMultiSet;
+import org.apache.commons.collections4.multiset.SynchronizedSortedMultiSet;
+import org.apache.commons.collections4.multiset.TreeMultiSet;
+import org.apache.commons.collections4.queue.SynchronizedQueue;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 /**
  * Extension of {@link AbstractCollectionTest} for exercising the
  * {@link SynchronizedCollection} implementation.
  */
 public class SynchronizedCollectionTest<E> extends AbstractCollectionTest<E> {
 
+    /** The elements used to populate each decorator under test. */
+    private static final List<String> ELEMENTS = Arrays.asList("a", "b");
+
+    /**
+     * Every decorator that inherits {@link SynchronizedCollection#forEach(java.util.function.Consumer)}.
+     */
+    static Stream<Arguments> getSynchronizedDecorators() {
+        return Stream.of(
+                arguments("SynchronizedCollection", SynchronizedCollection.synchronizedCollection(new ArrayList<>(ELEMENTS))),
+                arguments("SynchronizedBag", SynchronizedBag.synchronizedBag(new HashBag<>(ELEMENTS))),
+                arguments("SynchronizedSortedBag", SynchronizedSortedBag.synchronizedSortedBag(new TreeBag<>(ELEMENTS))),
+                arguments("SynchronizedMultiSet", SynchronizedMultiSet.synchronizedMultiSet(new HashMultiSet<>(ELEMENTS))),
+                arguments("SynchronizedSortedMultiSet", SynchronizedSortedMultiSet.synchronizedSortedMultiSet(new TreeMultiSet<>(ELEMENTS))),
+                arguments("SynchronizedQueue", SynchronizedQueue.synchronizedQueue(new LinkedList<>(ELEMENTS))));
+    }
+
     @Override
     public String getCompatibilityVersion() {
         return "4";
@@ -46,6 +82,18 @@ public Collection<E> makeObject() {
         return SynchronizedCollection.synchronizedCollection(new ArrayList<>());
     }
 
+    @ParameterizedTest(name = "{0}")
+    @MethodSource("getSynchronizedDecorators")
+    void testForEachHoldsLock(final String description, final Collection<String> decorator) {
+        final List<String> visited = new ArrayList<>();
+        decorator.forEach(element -> {
+            assertTrue(Thread.holdsLock(decorator), () -> description + " ran forEach without holding its lock");
+            visited.add(element);
+        });
+        assertEquals(ELEMENTS.size(), visited.size());
+        assertTrue(visited.containsAll(ELEMENTS));
+    }
+
 //    void testCreate() throws Exception {
 //        resetEmpty();
 //        writeExternalFormToDisk((java.io.Serializable) getCollection(), "src/test/resources/data/test/SynchronizedCollection.emptyCollection.version4.obj");