Patch caching fid in memory on successful registration. (#1764)

* Revert "Completing getId call with the disk reads on the caller thread.   (#1570)"

This reverts commit 1a36dd7

* Updating caching FID implementation due to the revert PR.

* Addressing Rayo's comments.

* Minor spacing.

* Addressing Rayo's comments.

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -66,6 +66,10 @@ public class FirebaseInstallations implements FirebaseInstallationsApi {
   private final Object lock = new Object();
   private final ExecutorService backgroundExecutor;
   private final ExecutorService networkExecutor;
+  /* FID of this Firebase Installations instance. Cached after successfully registering and
+  persisting the FID locally. NOTE: cachedFid resets if FID is deleted.*/
+  @GuardedBy("this")
+  private String cachedFid;
 
   @GuardedBy("lock")
   private final List<StateListener> listeners = new ArrayList<>();
@@ -221,8 +225,15 @@ String getName() {
   @Override
   public Task<String> getId() {
     preConditionChecks();
+
+    // Return cached fid if available.
+    String fid = getCacheFid();
+    if (fid != null) {
+      return Tasks.forResult(fid);
+    }
+
     Task<String> task = addGetIdListener();
-    backgroundExecutor.execute(this::doGetId);
+    backgroundExecutor.execute(() -> doRegistrationOrRefresh(false));
     return task;
   }
 
@@ -239,11 +250,7 @@ public Task<String> getId() {
   public Task<InstallationTokenResult> getToken(boolean forceRefresh) {
     preConditionChecks();
     Task<InstallationTokenResult> task = addGetAuthTokenListener();
-    if (forceRefresh) {
-      backgroundExecutor.execute(this::doGetAuthTokenForceRefresh);
-    } else {
-      backgroundExecutor.execute(this::doGetAuthTokenWithoutForceRefresh);
-    }
+    backgroundExecutor.execute(() -> doRegistrationOrRefresh(forceRefresh));
     return task;
   }
 
@@ -261,20 +268,22 @@ public Task<Void> delete() {
   private Task<String> addGetIdListener() {
     TaskCompletionSource<String> taskCompletionSource = new TaskCompletionSource<>();
     StateListener l = new GetIdListener(taskCompletionSource);
-    synchronized (lock) {
-      listeners.add(l);
-    }
+    addStateListeners(l);
     return taskCompletionSource.getTask();
   }
 
   private Task<InstallationTokenResult> addGetAuthTokenListener() {
     TaskCompletionSource<InstallationTokenResult> taskCompletionSource =
         new TaskCompletionSource<>();
     StateListener l = new GetAuthTokenListener(utils, taskCompletionSource);
+    addStateListeners(l);
+    return taskCompletionSource.getTask();
+  }
+
+  private void addStateListeners(StateListener l) {
     synchronized (lock) {
       listeners.add(l);
     }
-    return taskCompletionSource.getTask();
   }
 
   private void triggerOnStateReached(PersistedInstallationEntry persistedInstallationEntry) {
@@ -303,16 +312,12 @@ private void triggerOnException(PersistedInstallationEntry prefs, Exception exce
     }
   }
 
-  private final void doGetId() {
-    doRegistrationInternal(false);
-  }
-
-  private final void doGetAuthTokenWithoutForceRefresh() {
-    doRegistrationInternal(false);
+  private synchronized void updateCacheFid(String cachedFid) {
+    this.cachedFid = cachedFid;
   }
 
-  private final void doGetAuthTokenForceRefresh() {
-    doRegistrationInternal(true);
+  private synchronized String getCacheFid() {
+    return cachedFid;
   }
 
   /**
@@ -324,7 +329,8 @@ private final void doGetAuthTokenForceRefresh() {
    * @param forceRefresh true if this is for a getAuthToken call and if the caller wants to fetch a
    *     new auth token from the server even if an unexpired auth token exists on the client.
    */
-  private final void doRegistrationInternal(boolean forceRefresh) {
+  private final void doRegistrationOrRefresh(boolean forceRefresh) {
+
     PersistedInstallationEntry prefs = getPrefsWithGeneratedIdMultiProcessSafe();
 
     // Since the caller wants to force an authtoken refresh remove the authtoken from the
@@ -361,6 +367,11 @@ private void doNetworkCallIfNecessary(boolean forceRefresh) {
     // Store the prefs to persist the result of the previous step.
     insertOrUpdatePrefs(prefs);
 
+    // Update cachedFID, if FID is successfully REGISTERED and persisted.
+    if (prefs.isRegistered()) {
+      updateCacheFid(prefs.getFirebaseInstallationId());
+    }
+
     // Let the caller know about the result.
     if (prefs.isErrored()) {
       triggerOnException(prefs, new FirebaseInstallationsException(Status.BAD_CONFIG));
@@ -520,6 +531,7 @@ private PersistedInstallationEntry fetchAuthTokenFromServer(
       case AUTH_ERROR:
         // The the server refused to generate a new auth token due to bad credentials, clear the
         // FID to force the generation of a new one.
+        updateCacheFid(null);
         return prefs.withNoGeneratedFid();
       default:
         throw new FirebaseInstallationsException(
@@ -533,6 +545,7 @@ private PersistedInstallationEntry fetchAuthTokenFromServer(
    * storage.
    */
   private Void deleteFirebaseInstallationId() throws FirebaseInstallationsException {
+    updateCacheFid(null);
     PersistedInstallationEntry entry = getMultiProcessSafePrefs();
     if (entry.isRegistered()) {
       // Call the FIS servers to delete this Firebase Installation Id.
@@ -542,7 +555,6 @@ private Void deleteFirebaseInstallationId() throws FirebaseInstallationsExceptio
           /*projectID= */ getProjectIdentifier(),
           /*refreshToken= */ entry.getRefreshToken());
     }
-
     insertOrUpdatePrefs(entry.withNoGeneratedFid());
     return null;
   }

firebase-installations/src/main/java/com/google/firebase/installations/GetIdListener.java

@@ -17,6 +17,10 @@
 import com.google.android.gms.tasks.TaskCompletionSource;
 import com.google.firebase.installations.local.PersistedInstallationEntry;
 
+/**
+ * This class manages {@link PersistedInstallationEntry} state transitions valid for getId() and
+ * updates the caller once the id is generated.
+ */
 class GetIdListener implements StateListener {
   final TaskCompletionSource<String> taskCompletionSource;
 
@@ -32,6 +36,8 @@ public boolean onStateReached(PersistedInstallationEntry persistedInstallationEn
       taskCompletionSource.trySetResult(persistedInstallationEntry.getFirebaseInstallationId());
       return true;
     }
+    // Don't update the caller if the PersistedInstallationEntry registration status is
+    // ATTEMPT_MIGRATION or NOT_GENERATED.
     return false;
   }