Cherry Pick #1227 to Branch 3.0.x -> Fixing bug : Avoid registering s…

…ubscriber class multiple times (#1230)

* 2.2.x Fixing bug : Avoid registering subscriber class multiple times (#1227)

* Fixing bug to avoid registering subscriber class multiple times

* Refactoring for Singleton pattern

* cherry pick #1227

gcs/src/main/java/com/google/cloud/hadoop/fs/gcs/GoogleCloudStorageEventSubscriber.java

@@ -19,19 +19,40 @@
 import com.google.api.client.googleapis.json.GoogleJsonResponseException;
 import com.google.api.client.http.HttpResponseException;
 import com.google.cloud.hadoop.util.GcsRequestExecutionEvent;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.eventbus.Subscribe;
+import com.google.common.flogger.GoogleLogger;
 import io.grpc.Status;
 import java.io.IOException;
 import javax.annotation.Nonnull;
 
 /* Stores the subscriber methods corresponding to GoogleCloudStorageEventBus */
 public class GoogleCloudStorageEventSubscriber {
+  private static final GoogleLogger logger = GoogleLogger.forEnclosingClass();
   private static GhfsGlobalStorageStatistics storageStatistics;
+  private static GoogleCloudStorageEventSubscriber INSTANCE = null;
 
-  public GoogleCloudStorageEventSubscriber(GhfsGlobalStorageStatistics storageStatistics) {
+  private GoogleCloudStorageEventSubscriber(GhfsGlobalStorageStatistics storageStatistics) {
     this.storageStatistics = storageStatistics;
   }
 
+  /*
+   * Singleton class such that registration of subscriber methods is only once.
+   * */
+  public static synchronized GoogleCloudStorageEventSubscriber getInstance(
+      @Nonnull GhfsGlobalStorageStatistics storageStatistics) {
+    if (INSTANCE == null) {
+      logger.atFiner().log("Subscriber class invoked for first time");
+      INSTANCE = new GoogleCloudStorageEventSubscriber(storageStatistics);
+    }
+    return INSTANCE;
+  }
+
+  @VisibleForTesting
+  protected static void reset() {
+    INSTANCE = null;
+  }
+
   /**
    * Updating the required gcs specific statistics based on HttpResponseException.
    *

gcs/src/main/java/com/google/cloud/hadoop/fs/gcs/GoogleHadoopFileSystem.java

@@ -250,7 +250,7 @@ public GoogleHadoopFileSystem() {
     }
 
     GoogleCloudStorageEventBus.register(
-        new GoogleCloudStorageEventSubscriber(globalStorageStatistics));
+        GoogleCloudStorageEventSubscriber.getInstance(globalStorageStatistics));
   }
 
   /**

gcs/src/test/java/com/google/cloud/hadoop/fs/gcs/GoogleCloudStorageStatisticsTest.java

@@ -49,7 +49,7 @@ public class GoogleCloudStorageStatisticsTest {
   private static final GoogleLogger logger = GoogleLogger.forEnclosingClass();
   private GhfsGlobalStorageStatistics storageStatistics = new GhfsGlobalStorageStatistics();
   protected GoogleCloudStorageEventSubscriber subscriber =
-      new GoogleCloudStorageEventSubscriber(storageStatistics);
+      GoogleCloudStorageEventSubscriber.getInstance(storageStatistics);
 
   @Before
   public void setUp() throws Exception {
@@ -59,6 +59,7 @@ public void setUp() throws Exception {
   @After
   public void cleanup() throws Exception {
     GoogleCloudStorageEventBus.unregister(subscriber);
+    GoogleCloudStorageEventSubscriber.reset();
   }
 
   private void verifyStatistics(GhfsGlobalStorageStatistics expectedStats) {
@@ -78,6 +79,21 @@ private void verifyStatistics(GhfsGlobalStorageStatistics expectedStats) {
     assertThat(metricsVerified).isTrue();
   }
 
+  @Test
+  public void test_multiple_register_of_statistics() throws Exception {
+    GoogleCloudStorageEventBus.register(subscriber);
+    GoogleCloudStorageEventBus.register(subscriber);
+    GoogleCloudStorageEventBus.register(
+        GoogleCloudStorageEventSubscriber.getInstance(storageStatistics));
+    GoogleCloudStorageEventBus.register(
+        GoogleCloudStorageEventSubscriber.getInstance(storageStatistics));
+
+    GoogleCloudStorageEventBus.onGcsRequest(new GcsRequestExecutionEvent());
+    GhfsGlobalStorageStatistics verifyCounterStats = new GhfsGlobalStorageStatistics();
+    verifyCounterStats.incrementCounter(GCS_API_REQUEST_COUNT, 1);
+    verifyStatistics(verifyCounterStats);
+  }
+
   @Test
   public void gcs_requestCounter() throws Exception {
     GoogleCloudStorageEventBus.onGcsRequest(new GcsRequestExecutionEvent());

gcs/src/test/java/com/google/cloud/hadoop/fs/gcs/GoogleHadoopFileSystemIntegrationTest.java

@@ -77,6 +77,7 @@
 import com.google.cloud.hadoop.gcsio.testing.InMemoryGoogleCloudStorage;
 import com.google.cloud.hadoop.util.AccessTokenProvider;
 import com.google.cloud.hadoop.util.ApiErrorExtractor;
+import com.google.cloud.hadoop.util.GoogleCloudStorageEventBus;
 import com.google.cloud.hadoop.util.HadoopCredentialsConfiguration.AuthenticationType;
 import com.google.cloud.hadoop.util.testing.TestingAccessTokenProvider;
 import com.google.common.collect.ImmutableList;
@@ -2423,6 +2424,32 @@ public void testHnBucketDeleteOperationOnNonExistingFolder() throws Exception {
     }
   }
 
+  @Test
+  public void register_subscriber_multiple_time() throws Exception {
+    GoogleHadoopFileSystem myGhfs =
+        createInMemoryGoogleHadoopFileSystem(); // registers the subscriber class first time in
+    // myGhfs1
+    StorageStatistics stats = TestUtils.getStorageStatistics();
+
+    GoogleCloudStorageEventBus.register(
+        GoogleCloudStorageEventSubscriber.getInstance(
+            (GhfsGlobalStorageStatistics)
+                stats)); // registers the same subscriber class second time
+
+    assertThat(getMetricValue(stats, INVOCATION_CREATE)).isEqualTo(0);
+    assertThat(getMetricValue(stats, FILES_CREATED)).isEqualTo(0);
+
+    try (FSDataOutputStream fout = myGhfs.create(new Path("/file1"))) {
+      fout.writeBytes("Test Content");
+    }
+    assertThat(getMetricValue(stats, INVOCATION_CREATE)).isEqualTo(1);
+    assertThat(getMetricValue(stats, FILES_CREATED)).isEqualTo(1);
+    assertThat(myGhfs.delete(new Path("/file1"))).isTrue();
+
+    TestUtils.verifyDurationMetric(
+        (GhfsGlobalStorageStatistics) stats, INVOCATION_CREATE.getSymbol(), 1);
+  }
+
   private void createFile(GoogleHadoopFileSystem googleHadoopFileSystem, Path path)
       throws Exception {
     try (FSDataOutputStream fout = googleHadoopFileSystem.create(path)) {