[Android] Adding scheduling through GcmNetworkManager

components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerPrefs.java

+// Copyright 2017 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.components.background_task_scheduler;
+
+import android.content.SharedPreferences;
+
+import org.chromium.base.ContextUtils;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Class handling shared preference entries for BackgroundTaskScheduler.
+ */
+public class BackgroundTaskSchedulerPrefs {
+    private static final String TAG = "BTSPrefs";
+    private static final String KEY_SCHEDULED_TASKS = "bts_scheduled_tasks";
+    private static final String KEY_LAST_OS_VERSION = "bts_last_os_version";
+    private static final String KEY_LAST_APP_VERSION = "bts_last_app_version";
+    private static final String ENTRY_SEPARATOR = ":";
+
+    /** Adds a task to scheduler's preferences, so that it can be rescheduled with OS upgrade. */
+    public static void addScheduledTask(TaskInfo taskInfo) {
+        SharedPreferences prefs = ContextUtils.getAppSharedPreferences();
+        Set<String> scheduledTasks =
+                prefs.getStringSet(KEY_SCHEDULED_TASKS, new HashSet<String>(1));
+        String prefsEntry = toSharedPreferenceEntry(taskInfo);
+        if (scheduledTasks.contains(prefsEntry)) return;
+
+        // Set returned from getStringSet() should not be modified.
+        scheduledTasks = new HashSet<>(scheduledTasks);
+        scheduledTasks.add(prefsEntry);
+        updateScheduledTasks(prefs, scheduledTasks);
+    }
+
+    /** Removes a task from scheduler's preferences. */
+    public static void removeScheduledTask(int taskId) {
+        SharedPreferences prefs = ContextUtils.getAppSharedPreferences();
+        Set<String> scheduledTasks = prefs.getStringSet(KEY_SCHEDULED_TASKS, new HashSet<String>());
+
+        String entryToRemove = null;
+        String taskSuffix = ENTRY_SEPARATOR + taskId;
+        for (String entry : scheduledTasks) {
+            if (entry.endsWith(taskSuffix)) {
+                entryToRemove = entry;
+                break;
+            }
+        }
+
+        // Entry matching taskId was not found.
+        if (entryToRemove == null) return;
+
+        // Set returned from getStringSet() should not be modified.
+        scheduledTasks = new HashSet<>(scheduledTasks);
+        scheduledTasks.remove(entryToRemove);
+        updateScheduledTasks(prefs, scheduledTasks);
+    }
+
+    /** Gets a set of scheduled task class names. */
+    public static Set<String> getScheduledTasks() {
+        SharedPreferences prefs = ContextUtils.getAppSharedPreferences();
+        Set<String> prefsEntries = prefs.getStringSet(KEY_SCHEDULED_TASKS, new HashSet<String>(1));

[nyquist, 2017/04/18 21:58:28]

Why do you create the set with an initial size of 1?

[fgorski, 2017/04/20 05:54:15]

I saw that pattern someplace in code. This is to create the smallest possible
set as default in case the prefs does not have anything, which seems to be rare
in our case and therefore I don't want to be using whatever the default size is.
Does that make sense?

I'll gladly remove that 1 or switch to null and initialize properly as a
separate step.

+        Set<String> scheduledTasksClassNames = new HashSet<>(prefsEntries.size());
+        for (String entry : prefsEntries) {
+            String[] entryParts = entry.split(ENTRY_SEPARATOR);

[nyquist, 2017/04/18 21:58:28]

Could all of |entry| ever be null by accident?

[fgorski, 2017/04/20 05:54:15]

That should never happen... (famous last words)
Because I update task prefs handling in rescheduling patch I'll gladly address
it there if you don't mind. (Otherwise I will happily cherry-pick between
patches.
https://codereview.chromium.org/2819703002/diff/20001/components/background_t...

+            if (entryParts.length != 2 || entryParts[0] == null || entryParts[0].isEmpty()) {

[nyquist, 2017/04/18 21:58:28]

Should we verify whether entryParts[1] is a parsable int?

[fgorski, 2017/04/20 05:54:15]

Ditto:
https://codereview.chromium.org/2819703002/diff/20001/components/background_t...

+                continue;
+            }
+            scheduledTasksClassNames.add(entryParts[0]);
+        }
+
+        return scheduledTasksClassNames;
+    }
+
+    private static void updateScheduledTasks(SharedPreferences prefs, Set<String> tasks) {
+        SharedPreferences.Editor editor = prefs.edit();
+        editor.putStringSet(KEY_SCHEDULED_TASKS, tasks);
+        editor.apply();
+    }
+
+    /**
+     * Converts a task info to a shared preference entry in the format:
+     * BACKGROUND_TASK_CLASS_NAME:TASK_ID.
+     * Task ID is necessary to be able to remove the entries from the shared preferences.
+     */
+    private static String toSharedPreferenceEntry(TaskInfo taskInfo) {
+        return taskInfo.getBackgroundTaskClass().getName() + ENTRY_SEPARATOR + taskInfo.getTaskId();
+    }
+}