Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/webapps/ActivityAssigner.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.webapps;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.util.Log;
+
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.VisibleForTesting;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Manages a rotating LRU buffer of WebappActivities to assign webapps to.
+ *
+ * In order to accommodate a limited number of WebappActivities with a potentially unlimited number
+ * of webapps, we have to rotate the available WebappActivities between the webapps we start up.
+ * Activities are reused in order of when they were last used, with the least recently used
+ * ones culled first.
+ *
+ * It is impossible to know whether Tasks have been removed from the Recent Task list without the
+ * GET_TASKS permission.  As a result, the list of Activities inside the Recent Task list will
+ * be highly unlikely to match the list maintained in memory.  Instead, we store the mapping as it
+ * was the last time we changed it, which allows us to launch webapps in the WebappActivity they
+ * were most recently associated with in cases where a user restarts a webapp from the Recent Tasks.
+ * Note that in situations where the user manually clears the app data, we will again have an
+ * incorrect mapping.
+ *
+ * Unless otherwise noted, all methods MUST be called on the UI thread to avoid threading issues.
+ *
+ * EXAMPLE:
+ * - 3 Activities are available for assignment (0, 1, 2).
+ * - 4 webapps exist (X, Y, Z, W).
+ *
+ *    ACTION        EFFECT                                                ACTIVITY LIST
+ * 0) Clean slate                                                         (0 -) (1 -) (2 -)
+ * 1) Start X       Assigned to Activity 0 and pushed back.               (1 -) (2 -) (0 X)
+ * 2) Start Y       Assigned to Activity 1 and pushed back.               (2 -) (0 X) (1 Y)
+ * 3) Start Z       Assigned to Activity 2 and pushed back.               (0 X) (1 Y) (2 Z)
+ * 4) Restart Y     Re-assigned to Activity 1 and pushed back.            (0 X) (2 Z) (1 Y)
+ * 4) Start W       Assigned to Activity 0 and pushed back.  X evicted.   (2 Z) (1 Y) (0 W)
+ * 5) Restart X     Assigned to Activity 2 and pushed back.  Z evicted.   (1 Y) (0 W) (2 X)
+ */
+public class ActivityAssigner {
+    private static final String TAG = "ActivityAssigner";
+
+    // Don't ever change this.  10 is enough for everyone.
+    static final int NUM_WEBAPP_ACTIVITIES = 10;
+
+    // A sanity check limit to ensure that we aren't reading an unreasonable number of preferences.
+    // This number is different from above because the number of WebappActivities available may
+    // change.
+    static final int MAX_WEBAPP_ACTIVITIES_EVER = 100;
+
+    // Don't ever change the package.  Left for backwards compatibility.
+    @VisibleForTesting
+    static final String PREF_PACKAGE = "com.google.android.apps.chrome.webapps";
+    static final String PREF_NUM_SAVED_ENTRIES = "ActivityAssigner.numSavedEntries";
+    static final String PREF_ACTIVITY_INDEX = "ActivityAssigner.activityIndex";
+    static final String PREF_WEBAPP_ID = "ActivityAssigner.webappId";
+
+    static final int INVALID_ACTIVITY_INDEX = -1;
+
+    private static ActivityAssigner sInstance;
+
+    private final Context mContext;
+    private final List<ActivityEntry> mActivityList;
+
+    static class ActivityEntry {
+        final int mActivityIndex;
+        final String mWebappId;
+
+        ActivityEntry(int activity, String webapp) {
+            mActivityIndex = activity;
+            mWebappId = webapp;
+        }
+    }
+
+    /**
+     * Returns the singleton instance, creating it if necessary.
+     */
+    public static ActivityAssigner instance(Context context) {
+        ThreadUtils.assertOnUiThread();
+        if (sInstance == null) {
+            sInstance = new ActivityAssigner(context);
+        }
+        return sInstance;
+    }
+
+    private ActivityAssigner(Context context) {
+        mContext = context.getApplicationContext();
+        mActivityList = new ArrayList<ActivityEntry>();
+
+        restoreActivityList();
+    }
+
+    /**
+     * Assigns the webapp with the given ID to one of the available WebappActivities.
+     * If we know that the webapp was previously launched in one of the Activities, re-use it.
+     * Otherwise, take the least recently used WebappActivity ID and use that.
+     * @param webappId ID of the webapp.
+     * @return Index of the Activity to use for the webapp.
+     */
+    int assign(String webappId) {
+        // Reuse a running Activity with the same ID, if it exists.
+        int activityIndex = checkIfAssigned(webappId);
+
+        // Allocate the one in the front of the list.
+        if (activityIndex == INVALID_ACTIVITY_INDEX) {
+            activityIndex = mActivityList.get(0).mActivityIndex;
+            ActivityEntry newEntry = new ActivityEntry(activityIndex, webappId);
+            mActivityList.set(0, newEntry);
+        }
+
+        markActivityUsed(activityIndex, webappId);
+        return activityIndex;
+    }
+
+    /**
+     * Checks if the webapp with the given ID has been assigned to an Activity already.
+     * @param webappId ID of the webapp being displayed.
+     * @return Index of the Activity for the webapp if assigned, INVALID_ACTIVITY_INDEX otherwise.
+     */
+    int checkIfAssigned(String webappId) {
+        if (webappId == null) {
+            return INVALID_ACTIVITY_INDEX;
+        }
+
+        // Go backwards in the queue to catch more recent instances of any duplicated webapps.
+        for (int i = mActivityList.size() - 1; i >= 0; i--) {
+            if (webappId.equals(mActivityList.get(i).mWebappId)) {
+                return mActivityList.get(i).mActivityIndex;
+            }
+        }
+        return INVALID_ACTIVITY_INDEX;
+    }
+
+    /**
+     * Moves a WebappActivity to the back of the queue, indicating that the Webapp is still in use
+     * and shouldn't be killed.
+     * @param activityIndex Index of the WebappActivity.
+     * @param webappId ID of the webapp being shown in the WebappActivity.
+     */
+    void markActivityUsed(int activityIndex, String webappId) {
+        // Find the entry corresponding to the Activity.
+        int elementIndex = findActivityElement(activityIndex);
+
+        if (elementIndex == -1) {
+            Log.e(TAG, "Failed to find WebappActivity entry: " + activityIndex + ", " + webappId);
+            return;
+        }
+
+        // We have to reassign the webapp ID in case WebappActivities get repurposed.
+        ActivityEntry updatedEntry = new ActivityEntry(activityIndex, webappId);
+        mActivityList.remove(elementIndex);
+        mActivityList.add(updatedEntry);
+        storeActivityList();
+    }
+
+    /**
+     * Finds the index of the ActivityElement corresponding to the given activityIndex.
+     * @param activityIndex Index of the activity to find.
+     * @return The index of the ActivityElement in the activity list, or -1 if it couldn't be found.
+     */
+    private int findActivityElement(int activityIndex) {
+        for (int elementIndex = 0; elementIndex < mActivityList.size(); elementIndex++) {
+            if (mActivityList.get(elementIndex).mActivityIndex == activityIndex) {
+                return elementIndex;
+            }
+        }
+        return -1;
+    }
+
+    /**
+     * Returns the current mapping between Activities and webapps.
+     */
+    @VisibleForTesting
+    List<ActivityEntry> getEntries() {
+        return mActivityList;
+    }
+
+    /**
+     * Restores/creates the mapping between webapps and WebappActivities.
+     * The logic is slightly complicated to future-proof against situations where the number of
+     * WebappActivities is changed.
+     */
+    private void restoreActivityList() {
+        boolean isMapDirty = false;
+        mActivityList.clear();
+
+        // Create a Set of indices corresponding to every possible Activity.
+        // As ActivityEntries are read, they are and removed from this list to indicate that the
+        // Activity has already been assigned.
+        Set<Integer> availableWebapps = new HashSet<Integer>();
+        for (int i = 0; i < NUM_WEBAPP_ACTIVITIES; ++i) {
+            availableWebapps.add(i);
+        }
+
+        // Restore any entries that were previously saved.  If it seems that the preferences have
+        // been corrupted somehow, just discard the whole map.
+        SharedPreferences prefs = mContext.getSharedPreferences(PREF_PACKAGE, Context.MODE_PRIVATE);
+        try {
+            final int numSavedEntries = prefs.getInt(PREF_NUM_SAVED_ENTRIES, 0);
+            if (numSavedEntries <= NUM_WEBAPP_ACTIVITIES) {
+                for (int i = 0; i < numSavedEntries; ++i) {
+                    String currentActivityIndexPref = PREF_ACTIVITY_INDEX + i;
+                    String currentWebappIdPref = PREF_WEBAPP_ID + i;
+
+                    int activityIndex = prefs.getInt(currentActivityIndexPref, i);
+                    String webappId = prefs.getString(currentWebappIdPref, null);
+                    ActivityEntry entry = new ActivityEntry(activityIndex, webappId);
+
+                    if (availableWebapps.remove(entry.mActivityIndex)) {
+                        mActivityList.add(entry);
+                    } else {
+                        // If the same activity was assigned to two different entries, or if the
+                        // number of activities changed, discard it and mark that it needs to be
+                        // rewritten.
+                        isMapDirty = true;
+                    }
+                }
+            }
+        } catch (ClassCastException exception) {
+            // Something went wrong reading the preferences.  Nuke everything.
+            mActivityList.clear();
+            availableWebapps.clear();
+            for (int i = 0; i < NUM_WEBAPP_ACTIVITIES; ++i) {
+                availableWebapps.add(i);
+            }
+        }
+
+        // Add entries for any missing WebappActivities.
+        for (Integer availableIndex : availableWebapps) {
+            ActivityEntry entry = new ActivityEntry(availableIndex, null);
+            mActivityList.add(entry);
+            isMapDirty = true;
+        }
+
+        if (isMapDirty) {
+            storeActivityList();
+        }
+    }
+
+    /**
+     * Saves the mapping between webapps and WebappActivities.
+     */
+    private void storeActivityList() {
+        SharedPreferences prefs = mContext.getSharedPreferences(PREF_PACKAGE, Context.MODE_PRIVATE);
+        SharedPreferences.Editor editor = prefs.edit();
+        editor.clear();
+        editor.putInt(PREF_NUM_SAVED_ENTRIES, mActivityList.size());
+        for (int i = 0; i < mActivityList.size(); ++i) {
+            String currentActivityIndexPref = PREF_ACTIVITY_INDEX + i;
+            String currentWebappIdPref = PREF_WEBAPP_ID + i;
+            editor.putInt(currentActivityIndexPref, mActivityList.get(i).mActivityIndex);
+            editor.putString(currentWebappIdPref, mActivityList.get(i).mWebappId);
+        }
+        editor.apply();
+    }
+}