SNAPSHOT more tests

Author: lukewhiting

server/src/test/java/org/elasticsearch/common/streams/StreamsPermissionsUtilsTests.java

@@ -17,6 +17,8 @@
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.stream.IntStream;
 
 import static org.hamcrest.Matchers.sameInstance;
 import static org.mockito.Mockito.any;
@@ -38,10 +40,30 @@ public void setup() {
         when(projectMetadataMock.custom(eq(StreamsMetadata.TYPE), any())).thenReturn(streamsMetadataMock);
     }
 
-    public void testGetInstanceReturnsSingleton() {
-        StreamsPermissionsUtils instance1 = StreamsPermissionsUtils.getInstance();
-        StreamsPermissionsUtils instance2 = StreamsPermissionsUtils.getInstance();
-        assertThat(instance1, sameInstance(instance2));
+    public void testGetInstanceIsSingletonUnderMultithreadedAccess() throws Exception {
+        int threadCount = 20;
+        StreamsPermissionsUtils[] instances = new StreamsPermissionsUtils[threadCount];
+        CountDownLatch startLatch = new CountDownLatch(1);
+        CountDownLatch doneLatch = new CountDownLatch(threadCount);
+
+        IntStream.range(0, threadCount).forEach(i -> new Thread(() -> {
+            try {
+                startLatch.await();
+                instances[i] = StreamsPermissionsUtils.getInstance();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            } finally {
+                doneLatch.countDown();
+            }
+        }).start());
+
+        startLatch.countDown();
+        doneLatch.await();
+
+        StreamsPermissionsUtils first = instances[0];
+        for (int i = 1; i < threadCount; i++) {
+            assertThat(instances[i], sameInstance(first));
+        }
     }
 
     public void testStreamTypeIsEnabledReturnsTrueWhenLogsEnabled() {