Address Denver's feedback

Author: cherylEnkidu

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -49,6 +49,7 @@
 import com.google.firebase.firestore.model.ResourcePath;
 import com.google.firebase.firestore.remote.FirestoreChannel;
 import com.google.firebase.firestore.remote.GrpcMetadataProvider;
+import com.google.firebase.firestore.util.Assert;
 import com.google.firebase.firestore.util.AsyncQueue;
 import com.google.firebase.firestore.util.ByteBufferInputStream;
 import com.google.firebase.firestore.util.Executors;
@@ -63,6 +64,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicReference;
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -105,7 +107,9 @@ public interface InstanceRegistry {
   private volatile FirestoreClient client;
   private final GrpcMetadataProvider metadataProvider;
 
-  @Nullable private PersistentCacheIndexManager persistentCacheIndexManager;
+  @Nullable
+  private AtomicReference<PersistentCacheIndexManager> persistentCacheIndexManager =
+      new AtomicReference<>();
 
   @NonNull
   private static FirebaseApp getDefaultFirebaseApp() {
@@ -418,14 +422,15 @@ public Task<Void> setIndexConfiguration(@NonNull String json) {
   @Nullable
   public PersistentCacheIndexManager getPersistentCacheIndexManager() {
     ensureClientConfigured();
-    if (persistentCacheIndexManager != null) {
-      return persistentCacheIndexManager;
-    }
+    Assert.hardAssertNonNull(
+        persistentCacheIndexManager, "persistentCacheIndexManager has not been initialized.");
+
     if (settings.isPersistenceEnabled()
         || settings.getCacheSettings() instanceof PersistentCacheSettings) {
-      persistentCacheIndexManager = new PersistentCacheIndexManager(client);
+      persistentCacheIndexManager.compareAndSet(null, new PersistentCacheIndexManager(client));
     }
-    return persistentCacheIndexManager;
+
+    return persistentCacheIndexManager.get();
   }
 
   /**

firebase-firestore/src/main/java/com/google/firebase/firestore/PersistentCacheIndexManager.java

@@ -27,7 +27,7 @@
 // TODO(csi): Remove the `hide` and scope annotations.
 /** @hide */
 @RestrictTo(RestrictTo.Scope.LIBRARY)
-public class PersistentCacheIndexManager {
+public final class PersistentCacheIndexManager {
   @NonNull private FirestoreClient client;
 
   @RestrictTo(RestrictTo.Scope.LIBRARY)

firebase-firestore/src/main/java/com/google/firebase/firestore/local/QueryContext.java

@@ -16,16 +16,14 @@
 
 /** A tracker to keep a record of important details during database local query execution. */
 public class QueryContext {
-  public QueryContext() {}
-
   /** Counts the number of documents passed through during local query execution. */
   private int documentReadCount = 0;
 
   public int getDocumentReadCount() {
     return documentReadCount;
   }
 
-  public void increaseDocumentCount() {
+  public void incrementDocumentReadCount() {
     documentReadCount++;
   }
 }

firebase-firestore/src/main/java/com/google/firebase/firestore/local/QueryEngine.java

@@ -105,7 +105,7 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
     QueryContext context = new QueryContext();
     result = executeFullCollectionScan(query, context);
     if (result != null && automaticIndexingEnabled) {
-      CreateCacheIndexes(query, context, result.size());
+      createCacheIndexes(query, context, result.size());
     }
     return result;
   }
@@ -115,7 +115,7 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
    * context and query result size.
    */
   // TODO(csi): Auto experiment data.
-  private void CreateCacheIndexes(Query query, QueryContext context, int resultSize) {
+  private void createCacheIndexes(Query query, QueryContext context, int resultSize) {
     if (context.getDocumentReadCount() < minCollectionSizeToAutoCreateIndex) {
       Logger.debug(
           LOG_TAG,

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteIndexManager.java

@@ -241,7 +241,7 @@ public void createTargetIndices(Target target) {
       IndexType type = getIndexType(subTarget);
       if (type == IndexType.NONE || type == IndexType.PARTIAL) {
         TargetIndexMatcher targetIndexMatcher = new TargetIndexMatcher(subTarget);
-        addFieldIndex(targetIndexMatcher.BuildTargetIndex());
+        addFieldIndex(targetIndexMatcher.buildTargetIndex());
       }
     }
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteRemoteDocumentCache.java

@@ -224,7 +224,7 @@ private Map<DocumentKey, MutableDocument> getAll(
               processRowInBackground(backgroundQueue, results, row, filter);
               if (context != null) {
                 // Increases the counter by 1 for every document processed.
-                context.increaseDocumentCount();
+                context.incrementDocumentReadCount();
               }
             });
     backgroundQueue.drain();

firebase-firestore/src/main/java/com/google/firebase/firestore/model/TargetIndexMatcher.java

@@ -193,7 +193,7 @@ public boolean servedByIndex(FieldIndex index) {
   }
 
   /** Returns a full matched field index for this target. */
-  public FieldIndex BuildTargetIndex() {
+  public FieldIndex buildTargetIndex() {
     // We want to make sure only one segment created for one field. For example, in case like
     // a == 3 and a > 2, index, a ASCENDING, will only be created once.
     Set<FieldPath> uniqueFields = new HashSet<>();

firebase-firestore/src/test/java/com/google/firebase/firestore/model/TargetIndexMatcherTest.java

@@ -815,7 +815,7 @@ public void testBuildTargetIndexWithInAndOrderBySameField() {
   private void validateBuildTargetIndexCreateFullMatchIndex(Query query) {
     Target target = query.toTarget();
     TargetIndexMatcher targetIndexMatcher = new TargetIndexMatcher(target);
-    FieldIndex expectedIndex = targetIndexMatcher.BuildTargetIndex();
+    FieldIndex expectedIndex = targetIndexMatcher.buildTargetIndex();
     assertTrue(targetIndexMatcher.servedByIndex(expectedIndex));
     // Check the index created is a FULL MATCH index
     assertTrue(expectedIndex.getSegments().size() >= target.getSegmentCount());