Revert of Refactor WebappRegistry into a singleton instance.

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
index 1b15b9a0867eaf2d06cfcc044e444a2686a7005a..629aef6de6f64b70fc45a7eef4bedf8f0074ba74 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java
@@ -18,24 +18,18 @@
 import org.chromium.chrome.browser.browsing_data.UrlFilterBridge;
 
 import java.util.Collections;
-import java.util.HashMap;
-import java.util.Iterator;
+import java.util.HashSet;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 /**
- * Singleton class which tracks web apps backed by a SharedPreferences file (abstracted by the
- * WebappDataStorage class). This class is not thread-safe and must be used on the UI thread.
+ * Keeps track of web apps which have created a SharedPreference file (through the used of the
+ * WebappDataStorage class) which may need to be cleaned up in the future.
  *
- * Aside from web app registration, which is asynchronous as a new SharedPreferences file must be
- * opened, all methods in this class are synchronous. All web app SharedPreferences known to
- * WebappRegistry are pre-warmed on browser startup when creating the singleton WebappRegistry
- * instance, whilst registering a new web app will automatically cache the new SharedPreferences
- * after it is created.
- *
- * This class is not a comprehensive list of installed web apps because it is impossible to know
- * when the user removes a web app from the home screen. The WebappDataStorage.wasLaunchedRecently()
- * heuristic attempts to compensate for this.
+ * It is NOT intended to be 100% accurate nor a comprehensive list of all installed web apps
+ * because it is impossible to track when the user removes a web app from the Home screen and it
+ * is similarily impossible to track pre-registry era web apps (this case is not a problem anyway
+ * as these web apps have no external data to cleanup).
  */
 public class WebappRegistry {
 
@@ -49,49 +43,19 @@
     /** Represents a period of 13 weeks in milliseconds */
     static final long WEBAPP_UNOPENED_CLEANUP_DURATION = TimeUnit.DAYS.toMillis(13L * 7L);
 
-    private static volatile WebappRegistry sInstance;
-
-    private HashMap<String, WebappDataStorage> mStorages;
-    private SharedPreferences mPreferences;
-
-    /**
-     * Callback run when a WebappDataStorage object is registered for the first time. The storage
-     * parameter will never be null.
+    /**
+     * Called when a retrieval of the set of stored web app IDs occurs.
+     */
+    public interface FetchCallback {
+        void onWebappIdsRetrieved(Set<String> readObject);
+    }
+
+    /**
+     * Called when a retrieval of the stored WebappDataStorage occurs. The storage parameter will
+     * be null if the web app queried for was not in the registry.
      */
     public interface FetchWebappDataStorageCallback {
         void onWebappDataStorageRetrieved(WebappDataStorage storage);
-    }
-
-    /**
-     * Returns the singleton WebappRegistry instance. Creates the instance if necessary.
-     */
-    public static WebappRegistry getInstance() {
-        assert ThreadUtils.runningOnUiThread();
-        if (sInstance == null) sInstance = new WebappRegistry();
-        return sInstance;
-    }
-
-    /**
-     * Warm up the WebappRegistry and a specific WebappDataStorage SharedPreferences. This static
-     * method can be called on any thread, so it must not initialize sInstance.
-     * @param id The web app id to warm up in addition to the WebappRegistry.
-     */
-    public static void warmUpSharedPrefsForId(String id) {
-        sInstance.initStorages(id, false);
-    }
-
-    /**
-     * Warm up the WebappRegistry and all WebappDataStorage SharedPreferences. This static method
-     * can be called on any thread, so it must not initialize sInstance.
-     */
-    public static void warmUpSharedPrefs() {
-        sInstance.initStorages(null, false);
-    }
-
-    public static void refreshSharedPrefsForTesting() {
-        assert ThreadUtils.runningOnUiThread();
-        sInstance = new WebappRegistry();
-        sInstance.initStorages(null, true);
     }
 
     /**
@@ -101,200 +65,275 @@
      * @param callback The callback to run with the WebappDataStorage argument.
      * @return The storage object for the web app.
      */
-    public void register(final String webappId, final FetchWebappDataStorageCallback callback) {
-        assert ThreadUtils.runningOnUiThread();
-
+    public static void registerWebapp(final String webappId,
+            final FetchWebappDataStorageCallback callback) {
         new AsyncTask<Void, Void, WebappDataStorage>() {
             @Override
             protected final WebappDataStorage doInBackground(Void... nothing) {
-                // Create the WebappDataStorage on the background thread, as this must create and
-                // open a new SharedPreferences.
-                return WebappDataStorage.open(webappId);
+                SharedPreferences preferences = openSharedPreferences();
+                // The set returned by getRegisteredWebappIds must be treated as immutable, so we
+                // make a copy to edit and save.
+                Set<String> webapps = new HashSet<>(getRegisteredWebappIds(preferences));
+                boolean added = webapps.add(webappId);
+                assert added;
+
+                preferences.edit().putStringSet(KEY_WEBAPP_SET, webapps).apply();
+
+                // Create the WebappDataStorage and update the last used time, so we can guarantee
+                // that a web app which appears in the registry will have a
+                // last used time != WebappDataStorage.LAST_USED_INVALID.
+                WebappDataStorage storage = new WebappDataStorage(webappId);
+                storage.updateLastUsedTime();
+                return storage;
             }
 
             @Override
             protected final void onPostExecute(WebappDataStorage storage) {
-                // Guarantee that last used time != WebappDataStorage.LAST_USED_INVALID. Must be
-                // run on the main thread as SharedPreferences.Editor.apply() is called.
-                mStorages.put(webappId, storage);
-                mPreferences.edit().putStringSet(KEY_WEBAPP_SET, mStorages.keySet()).apply();
-                storage.updateLastUsedTime();
                 if (callback != null) callback.onWebappDataStorageRetrieved(storage);
             }
         }.execute();
     }
 
     /**
-     * Returns the WebappDataStorage object for webappId, or null if one cannot be found.
-     * @param webappId The id of the web app.
+     * Runs the callback, supplying the WebappDataStorage object for webappId, or null if the web
+     * app has not been registered.
+     * @param webappId The id of the web app to register.
      * @return The storage object for the web app, or null if webappId is not registered.
      */
-    public WebappDataStorage getWebappDataStorage(String webappId) {
-        return mStorages.get(webappId);
-    }
-
-    /**
-     * Returns the WebappDataStorage object whose scope most closely matches the provided URL, or
-     * null if a matching web app cannot be found. The most closely matching scope is the longest
-     * scope which has the same prefix as the URL to open.
-     * @param url The URL to search for.
-     * @return The storage object for the web app, or null if one cannot be found.
-     */
-    public WebappDataStorage getWebappDataStorageForUrl(final String url) {
-        WebappDataStorage bestMatch = null;
-        int largestOverlap = 0;
-        for (HashMap.Entry<String, WebappDataStorage> entry : mStorages.entrySet()) {
-            WebappDataStorage storage = entry.getValue();
-            String scope = storage.getScope();
-            if (url.startsWith(scope) && scope.length() > largestOverlap) {
-                bestMatch = storage;
-                largestOverlap = scope.length();
-            }
-        }
-        return bestMatch;
-    }
-
-    /**
-     * Returns the list of web app IDs which are written to SharedPreferences.
+    public static void getWebappDataStorage(final String webappId,
+            final FetchWebappDataStorageCallback callback) {
+        new AsyncTask<Void, Void, WebappDataStorage>() {
+            @Override
+            protected final WebappDataStorage doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences();
+                if (getRegisteredWebappIds(preferences).contains(webappId)) {
+                    WebappDataStorage storage = WebappDataStorage.open(webappId);
+                    return storage;
+                }
+                return null;
+            }
+
+            @Override
+            protected final void onPostExecute(WebappDataStorage storage) {
+                assert callback != null;
+                callback.onWebappDataStorageRetrieved(storage);
+            }
+        }.execute();
+    }
+
+    /**
+     * Runs the callback, supplying the WebappDataStorage object whose scope most closely matches
+     * the provided URL, or null if a matching web app cannot be found. The most closely matching
+     * scope is the longest scope which has the same prefix as the URL to open.
+     * @param url      The URL to search for.
+     * @return The storage object for the web app, or null if webappId is not registered.
+     */
+    public static void getWebappDataStorageForUrl(final String url,
+            final FetchWebappDataStorageCallback callback) {
+        new AsyncTask<Void, Void, WebappDataStorage>() {
+            @Override
+            protected final WebappDataStorage doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences();
+                WebappDataStorage bestMatch = null;
+                int largestOverlap = 0;
+                for (String id : getRegisteredWebappIds(preferences)) {
+                    WebappDataStorage storage = WebappDataStorage.open(id);
+                    String scope = storage.getScope();
+                    if (url.startsWith(scope) && scope.length() > largestOverlap) {
+                        bestMatch = storage;
+                        largestOverlap = scope.length();
+                    }
+                }
+                return bestMatch;
+            }
+
+            protected final void onPostExecute(WebappDataStorage storage) {
+                assert callback != null;
+                callback.onWebappDataStorageRetrieved(storage);
+            }
+        }.execute();
+    }
+
+    /**
+     * Asynchronously retrieves the list of web app IDs which this registry is aware of.
+     * @param callback Called when the set has been retrieved. The set may be empty.
      */
     @VisibleForTesting
-    public static Set<String> getRegisteredWebappIdsForTesting() {
-        // Wrap with unmodifiableSet to ensure it's never modified. See crbug.com/568369.
-        return Collections.unmodifiableSet(openSharedPreferences().getStringSet(
-                KEY_WEBAPP_SET, Collections.<String>emptySet()));
-    }
-
-    /**
-     * Deletes the data for all "old" web apps, as well as all WebAPKs that have been uninstalled in
-     * the last month. "Old" web apps have not been opened by the user in the last 3 months, or have
-     * had their last used time set to 0 by the user clearing their history. Cleanup is run, at
-     * most, once a month.
+    public static void getRegisteredWebappIds(final FetchCallback callback) {
+        new AsyncTask<Void, Void, Set<String>>() {
+            @Override
+            protected final Set<String> doInBackground(Void... nothing) {
+                return getRegisteredWebappIds(openSharedPreferences());
+            }
+
+            @Override
+            protected final void onPostExecute(Set<String> result) {
+                assert callback != null;
+                callback.onWebappIdsRetrieved(result);
+            }
+        }.execute();
+    }
+
+    /**
+     * 1. Deletes the data for all "old" web apps.
+     * "Old" web apps have not been opened by the user in the last 3 months, or have had their last
+     * used time set to 0 by the user clearing their history. Cleanup is run, at most, once a month.
+     * 2. Deletes the data for all WebAPKs that have been uninstalled in the last month.
+     *
      * @param currentTime The current time which will be checked to decide if the task should be run
      *                    and if a web app should be cleaned up.
      */
-    public void unregisterOldWebapps(long currentTime) {
-        assert ThreadUtils.runningOnUiThread();
-        if ((currentTime - mPreferences.getLong(KEY_LAST_CLEANUP, 0)) < FULL_CLEANUP_DURATION) {
-            return;
-        }
-
-        Iterator<HashMap.Entry<String, WebappDataStorage>> it = mStorages.entrySet().iterator();
-        while (it.hasNext()) {
-            HashMap.Entry<String, WebappDataStorage> entry = it.next();
-            WebappDataStorage storage = entry.getValue();
-            String webApkPackage = storage.getWebApkPackageName();
-            if (webApkPackage != null) {
-                if (isWebApkInstalled(webApkPackage)) {
-                    continue;
-                }
-            } else if ((currentTime - storage.getLastUsedTime())
-                    < WEBAPP_UNOPENED_CLEANUP_DURATION) {
-                continue;
-            }
-            storage.delete();
-            it.remove();
-        }
-
-        mPreferences.edit()
-                .putLong(KEY_LAST_CLEANUP, currentTime)
-                .putStringSet(KEY_WEBAPP_SET, mStorages.keySet())
-                .apply();
-    }
-
-    /**
-     * Deletes the data of all web apps whose url matches |urlFilter|.
-     * @param urlFilter The filter object to check URLs.
-     */
-    @VisibleForTesting
-    void unregisterWebappsForUrlsImpl(UrlFilter urlFilter) {
-        assert ThreadUtils.runningOnUiThread();
-
-        Iterator<HashMap.Entry<String, WebappDataStorage>> it = mStorages.entrySet().iterator();
-        while (it.hasNext()) {
-            HashMap.Entry<String, WebappDataStorage> entry = it.next();
-            WebappDataStorage storage = entry.getValue();
-            if (urlFilter.matchesUrl(storage.getUrl())) {
-                storage.delete();
-                it.remove();
-            }
-        }
-
-        if (mStorages.isEmpty()) {
-            mPreferences.edit().clear().apply();
-        } else {
-            mPreferences.edit().putStringSet(KEY_WEBAPP_SET, mStorages.keySet()).apply();
-        }
-    }
-
-    @CalledByNative
-    static void unregisterWebappsForUrls(UrlFilterBridge urlFilter) {
-        WebappRegistry.getInstance().unregisterWebappsForUrlsImpl(urlFilter);
-        urlFilter.destroy();
-    }
-
-    /**
-     * Deletes the URL and scope, and sets the last used time to 0 for all web apps whose url
-     * matches |urlFilter|.
-     * @param urlFilter The filter object to check URLs.
-     */
-    @VisibleForTesting
-    void clearWebappHistoryForUrlsImpl(UrlFilter urlFilter) {
-        assert ThreadUtils.runningOnUiThread();
-
-        for (HashMap.Entry<String, WebappDataStorage> entry : mStorages.entrySet()) {
-            WebappDataStorage storage = entry.getValue();
-            if (urlFilter.matchesUrl(storage.getUrl())) {
-                storage.clearHistory();
-            }
-        }
-    }
-
-    @CalledByNative
-    static void clearWebappHistoryForUrls(UrlFilterBridge urlFilter) {
-        WebappRegistry.getInstance().clearWebappHistoryForUrlsImpl(urlFilter);
-        urlFilter.destroy();
-    }
-
-    /**
-     * Returns true if the given WebAPK is installed.
-     */
-    private boolean isWebApkInstalled(String webApkPackage) {
+    static void unregisterOldWebapps(final long currentTime) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences();
+                long lastCleanup = preferences.getLong(KEY_LAST_CLEANUP, 0);
+                if ((currentTime - lastCleanup) < FULL_CLEANUP_DURATION) return null;
+
+                Set<String> currentWebapps = getRegisteredWebappIds(preferences);
+                Set<String> retainedWebapps = new HashSet<>(currentWebapps);
+                PackageManager pm = ContextUtils.getApplicationContext().getPackageManager();
+                for (String id : currentWebapps) {
+                    WebappDataStorage storage = new WebappDataStorage(id);
+                    String webApkPackage = storage.getWebApkPackageName();
+                    if (webApkPackage != null) {
+                        if (isWebApkInstalled(pm, webApkPackage)) continue;
+                    } else {
+                        long lastUsed = storage.getLastUsedTime();
+                        if ((currentTime - lastUsed) < WEBAPP_UNOPENED_CLEANUP_DURATION) continue;
+                    }
+                    WebappDataStorage.deleteDataForWebapp(id);
+                    retainedWebapps.remove(id);
+                }
+
+                preferences.edit()
+                        .putLong(KEY_LAST_CLEANUP, currentTime)
+                        .putStringSet(KEY_WEBAPP_SET, retainedWebapps)
+                        .apply();
+                return null;
+            }
+        }.execute();
+    }
+
+    /**
+     * Returns whether the given WebAPK is still installed.
+     */
+    private static boolean isWebApkInstalled(PackageManager pm, String webApkPackage) {
+        assert !ThreadUtils.runningOnUiThread();
         try {
-            ContextUtils.getApplicationContext().getPackageManager().getPackageInfo(
-                    webApkPackage, PackageManager.GET_ACTIVITIES);
+            pm.getPackageInfo(webApkPackage, PackageManager.GET_ACTIVITIES);
         } catch (NameNotFoundException e) {
             return false;
         }
         return true;
     }
 
+    /**
+     * Deletes the data of all web apps whose url matches |urlFilter|, as well as the registry
+     * tracking those web apps.
+     */
+    @VisibleForTesting
+    static void unregisterWebappsForUrls(final UrlFilter urlFilter, final Runnable callback) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences();
+                Set<String> registeredWebapps =
+                        new HashSet<>(getRegisteredWebappIds(preferences));
+                Set<String> webappsToUnregister = new HashSet<>();
+                for (String id : registeredWebapps) {
+                    if (urlFilter.matchesUrl(WebappDataStorage.open(id).getUrl())) {
+                        WebappDataStorage.deleteDataForWebapp(id);
+                        webappsToUnregister.add(id);
+                    }
+                }
+
+                // TODO(dominickn): SharedPreferences should be accessed on the main thread, not
+                // from an AsyncTask. Simultaneous access from two threads creates a race condition.
+                // Update all callsites in this class.
+                registeredWebapps.removeAll(webappsToUnregister);
+                if (registeredWebapps.isEmpty()) {
+                    preferences.edit().clear().apply();
+                } else {
+                    preferences.edit().putStringSet(KEY_WEBAPP_SET, registeredWebapps).apply();
+                }
+
+                return null;
+            }
+
+            @Override
+            protected final void onPostExecute(Void nothing) {
+                assert callback != null;
+                callback.run();
+            }
+        }.execute();
+    }
+
+    @CalledByNative
+    static void unregisterWebappsForUrls(
+            final UrlFilterBridge urlFilter, final long callbackPointer) {
+        unregisterWebappsForUrls(urlFilter, new Runnable() {
+            @Override
+            public void run() {
+                urlFilter.destroy();
+                nativeOnWebappsUnregistered(callbackPointer);
+            }
+        });
+    }
+
+    /**
+     * Deletes the URL and scope, and sets the last used time to 0 for all web apps whose url
+     * matches |urlFilter|.
+     */
+    @VisibleForTesting
+    static void clearWebappHistoryForUrls(final UrlFilter urlFilter, final Runnable callback) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences();
+                for (String id : getRegisteredWebappIds(preferences)) {
+                    if (urlFilter.matchesUrl(WebappDataStorage.open(id).getUrl())) {
+                        WebappDataStorage.clearHistory(id);
+                    }
+                }
+                return null;
+            }
+
+            @Override
+            protected final void onPostExecute(Void nothing) {
+                assert callback != null;
+                callback.run();
+            }
+        }.execute();
+    }
+
+    @CalledByNative
+    static void clearWebappHistoryForUrls(
+            final UrlFilterBridge urlFilter, final long callbackPointer) {
+        clearWebappHistoryForUrls(urlFilter, new Runnable() {
+            @Override
+            public void run() {
+                urlFilter.destroy();
+                nativeOnClearedWebappHistory(callbackPointer);
+            }
+        });
+    }
+
     private static SharedPreferences openSharedPreferences() {
         return ContextUtils.getApplicationContext().getSharedPreferences(
                 REGISTRY_FILE_NAME, Context.MODE_PRIVATE);
     }
 
+    private static Set<String> getRegisteredWebappIds(SharedPreferences preferences) {
+        // Wrap with unmodifiableSet to ensure it's never modified. See crbug.com/568369.
+        return Collections.unmodifiableSet(
+                preferences.getStringSet(KEY_WEBAPP_SET, Collections.<String>emptySet()));
+    }
+
     private WebappRegistry() {
-        mPreferences = openSharedPreferences();
-        mStorages = new HashMap<String, WebappDataStorage>();
-    }
-
-    private void initStorages(String idToInitialize, boolean replaceExisting) {
-        Set<String> webapps =
-                mPreferences.getStringSet(KEY_WEBAPP_SET, Collections.<String>emptySet());
-        boolean initAll = (idToInitialize == null || idToInitialize.isEmpty());
-
-        // Don't overwrite any entry in mStorages unless replaceExisting is set to true.
-        if (initAll) {
-            for (String id : webapps) {
-                if (replaceExisting || !mStorages.containsKey(id)) {
-                    mStorages.put(id, WebappDataStorage.open(id));
-                }
-            }
-        } else {
-            if (webapps.contains(idToInitialize)
-                    && (replaceExisting || !mStorages.containsKey(idToInitialize))) {
-                mStorages.put(idToInitialize, WebappDataStorage.open(idToInitialize));
-            }
-        }
-    }
+    }
+
+    private static native void nativeOnWebappsUnregistered(long callbackPointer);
+    private static native void nativeOnClearedWebappHistory(long callbackPointer);
 }