Fix ConcurrentModificationException from nodes info and nodes stats

core/src/main/java/org/elasticsearch/action/admin/cluster/node/info/PluginsInfo.java

@@ -28,38 +28,33 @@
 import org.elasticsearch.plugins.PluginInfo;
 
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collections;
+import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
 
 public class PluginsInfo implements Streamable, ToXContent {
     static final class Fields {
         static final XContentBuilderString PLUGINS = new XContentBuilderString("plugins");
     }
 
-    private List<PluginInfo> infos;
+    private Set<PluginInfo> infos;
 
     public PluginsInfo() {
-        infos = new ArrayList<>();
-    }
-
-    public PluginsInfo(int size) {
-        infos = new ArrayList<>(size);
-    }
-
-    /**
-     * @return an ordered list based on plugins name
-     */
-    public List<PluginInfo> getInfos() {
-        Collections.sort(infos, new Comparator<PluginInfo>() {
+        infos = new TreeSet<>(new Comparator<PluginInfo>() {
             @Override
             public int compare(final PluginInfo o1, final PluginInfo o2) {
                 return o1.getName().compareTo(o2.getName());
             }
         });
+    }
 
-        return infos;
+    /**
+     * @return an ordered list based on plugins name
+     */
+    public List<PluginInfo> getInfos() {
+        return Arrays.asList(infos.toArray(new PluginInfo[infos.size()]));
     }
 
     public void add(PluginInfo info) {
@@ -75,6 +70,7 @@ public static PluginsInfo readPluginsInfo(StreamInput in) throws IOException {
     @Override
     public void readFrom(StreamInput in) throws IOException {
         int plugins_size = in.readInt();
+        infos.clear();
         for (int i = 0; i < plugins_size; i++) {
             infos.add(PluginInfo.readFromStream(in));
         }

core/src/test/java/org/elasticsearch/plugins/PluginInfoTests.java

@@ -28,8 +28,12 @@
 import java.io.OutputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.ConcurrentModificationException;
 import java.util.List;
 import java.util.Properties;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import static org.elasticsearch.common.util.CollectionUtils.eagerTransform;
 import static org.hamcrest.Matchers.contains;
@@ -273,7 +277,7 @@ public void testReadFromPropertiesSitePluginWithoutSite() throws Exception {
     }
 
     public void testPluginListSorted() {
-        PluginsInfo pluginsInfo = new PluginsInfo(5);
+        PluginsInfo pluginsInfo = new PluginsInfo();
         pluginsInfo.add(new PluginInfo("c", "foo", true, "dummy", true, "dummyclass", true));
         pluginsInfo.add(new PluginInfo("b", "foo", true, "dummy", true, "dummyclass", true));
         pluginsInfo.add(new PluginInfo("e", "foo", true, "dummy", true, "dummyclass", true));
@@ -289,4 +293,42 @@ public String apply(PluginInfo input) {
         });
         assertThat(names, contains("a", "b", "c", "d", "e"));
     }
+
+    public void testConcurrentModificationsAreAvoided() throws InterruptedException {
+        final PluginsInfo pluginsInfo = new PluginsInfo();
+        int numberOfPlugins = randomIntBetween(128, 256);
+        for (int i = 0; i < numberOfPlugins; i++) {
+            pluginsInfo.add(new PluginInfo("name", "description", false, "version", true, "classname", true));
+        }
+
+        int randomNumberOfThreads = randomIntBetween(2, 8);
+        final int numberOfAttempts = randomIntBetween(2048, 4096);
+        final CountDownLatch latch = new CountDownLatch(1 + randomNumberOfThreads);
+        List<Thread> threads = new ArrayList<>(randomNumberOfThreads);
+        final AtomicBoolean cme = new AtomicBoolean();
+        for (int i = 0; i < randomNumberOfThreads; i++) {
+            Thread thread = new Thread(new Runnable() {
+                @Override
+                public void run() {
+                    latch.countDown();
+                    for (int j = 0; j < numberOfAttempts; j++) {
+                        try {
+                            pluginsInfo.getInfos();
+                        } catch (ConcurrentModificationException e) {
+                            cme.set(true);
+                        }
+                    }
+                }
+            });
+            threads.add(thread);
+            thread.start();
+        }
+
+        latch.countDown();
+        for (Thread thread : threads) {
+            thread.join();
+        }
+
+        assertFalse(cme.get());
+    }
 }