[android] Add JobScheduler-based BackgroundTaskScheduler.

components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskJobService.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.annotation.TargetApi;
+import android.app.job.JobParameters;
+import android.app.job.JobService;
+import android.os.Build;
+
+import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/** Delegates calls out to various tasks that need to run in the background. */
+@TargetApi(Build.VERSION_CODES.LOLLIPOP_MR1)
+public class BackgroundTaskJobService extends JobService {
+    private static final String TAG = "BkgrdTaskJS";
+
+    private static class TaskFinishedCallbackJobService
+            implements BackgroundTask.TaskFinishedCallback {
+        private final BackgroundTaskJobService mJobService;
+        private final BackgroundTask mBackgroundTask;
+        private final JobParameters mParams;
+
+        TaskFinishedCallbackJobService(BackgroundTaskJobService jobService,
+                BackgroundTask backgroundTask, JobParameters params) {
+            mJobService = jobService;
+            mBackgroundTask = backgroundTask;
+            mParams = params;
+        }
+
+        @Override
+        public void taskFinished(final boolean needsReschedule) {
+            // Need to remove the current task from the currently running tasks. All other access
+            // happens on the main thread, so do this removal also on the main thread.
+            // To ensure that a new job is not immediately scheduled in between removing the task
+            // from being a current task and before calling jobFinished, leading to us finishing
+            // something with the same ID, call
+            // {@link JobService#jobFinished(JobParameters, boolean} also on the main thread.
+            ThreadUtils.runOnUiThreadBlocking(new Runnable() {
+                @Override
+                public void run() {
+                    if (!isCurrentBackgroundTaskForJobId()) {
+                        Log.e(TAG, "Tried finishing non-current BackgroundTask.");
+                        return;
+                    }
+
+                    mJobService.mCurrentTasks.remove(mParams.getJobId());
+                    mJobService.jobFinished(mParams, needsReschedule);
+                }
+            });
+        }
+
+        private boolean isCurrentBackgroundTaskForJobId() {
+            return mJobService.mCurrentTasks.get(mParams.getJobId()) == mBackgroundTask;
+        }
+    }
+
+    private final Map<Integer, BackgroundTask> mCurrentTasks = new HashMap<>();
+
+    @Override
+    public boolean onStartJob(JobParameters params) {
+        ThreadUtils.assertOnUiThread();
+        BackgroundTask backgroundTask =
+                BackgroundTaskSchedulerJobService.getBackgroundTaskFromJobParameters(params);
+        if (backgroundTask == null) {
+            Log.w(TAG, "Failed to start task. Could not instantiate class.");
+            return false;
+        }
+
+        mCurrentTasks.put(params.getJobId(), backgroundTask);
+
+        TaskParameters taskParams =
+                BackgroundTaskSchedulerJobService.getTaskParametersFromJobParameters(params);
+        boolean taskNeedsBackgroundProcessing = backgroundTask.onStartTask(getApplicationContext(),
+                taskParams, new TaskFinishedCallbackJobService(this, backgroundTask, params));
+
+        if (!taskNeedsBackgroundProcessing) mCurrentTasks.remove(params.getJobId());
+        return taskNeedsBackgroundProcessing;
+    }
+
+    @Override
+    public boolean onStopJob(JobParameters params) {
+        ThreadUtils.assertOnUiThread();
+        if (!mCurrentTasks.containsKey(params.getJobId())) {
+            Log.w(TAG, "Failed to stop job, because job with job id " + params.getJobId()
+                            + " does not exist.");
+            return false;
+        }
+
+        BackgroundTask backgroundTask = mCurrentTasks.get(params.getJobId());
+
+        TaskParameters taskParams =
+                BackgroundTaskSchedulerJobService.getTaskParametersFromJobParameters(params);
+        boolean taskNeedsReschedule =
+                backgroundTask.onStopTask(getApplicationContext(), taskParams);
+        mCurrentTasks.remove(params.getJobId());
+        return taskNeedsReschedule;
+    }
+}