RootScanner.java revision 0f32537e40ee2662d4f0b7b625ee280ca9c02066 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.mtp;
18
19import android.content.ContentResolver;
20import android.net.Uri;
21import android.os.Process;
22import android.provider.DocumentsContract;
23import android.util.Log;
24
25import java.io.FileNotFoundException;
26import java.util.concurrent.CountDownLatch;
27import java.util.concurrent.ExecutorService;
28import java.util.concurrent.Executors;
29import java.util.concurrent.FutureTask;
30import java.util.concurrent.TimeUnit;
31
32final class RootScanner {
33    /**
34     * Polling interval in milliseconds used for first SHORT_POLLING_TIMES because it is more
35     * likely to add new root just after the device is added.
36     */
37    private final static long SHORT_POLLING_INTERVAL = 2000;
38
39    /**
40     * Polling interval in milliseconds for low priority polling, when changes are not expected.
41     */
42    private final static long LONG_POLLING_INTERVAL = 30 * 1000;
43
44    /**
45     * @see #SHORT_POLLING_INTERVAL
46     */
47    private final static long SHORT_POLLING_TIMES = 10;
48
49    /**
50     * Milliseconds we wait for background thread when pausing.
51     */
52    private final static long AWAIT_TERMINATION_TIMEOUT = 2000;
53
54    final ContentResolver mResolver;
55    final MtpManager mManager;
56    final MtpDatabase mDatabase;
57
58    ExecutorService mExecutor;
59    FutureTask<Void> mCurrentTask;
60
61    RootScanner(
62            ContentResolver resolver,
63            MtpManager manager,
64            MtpDatabase database) {
65        mResolver = resolver;
66        mManager = manager;
67        mDatabase = database;
68    }
69
70    /**
71     * Notifies a change of the roots list via ContentResolver.
72     */
73    void notifyChange() {
74        final Uri uri = DocumentsContract.buildRootsUri(MtpDocumentsProvider.AUTHORITY);
75        mResolver.notifyChange(uri, null, false);
76    }
77
78    /**
79     * Starts to check new changes right away.
80     */
81    synchronized CountDownLatch resume() {
82        if (mExecutor == null) {
83            // Only single thread updates the database.
84            mExecutor = Executors.newSingleThreadExecutor();
85        }
86        if (mCurrentTask != null) {
87            // Cancel previous task.
88            mCurrentTask.cancel(true);
89        }
90        final UpdateRootsRunnable runnable = new UpdateRootsRunnable();
91        mCurrentTask = new FutureTask<Void>(runnable, null);
92        mExecutor.submit(mCurrentTask);
93        return runnable.mFirstScanCompleted;
94    }
95
96    /**
97     * Stops background thread and wait for its termination.
98     * @throws InterruptedException
99     */
100    synchronized void pause() throws InterruptedException {
101        if (mExecutor == null) {
102            return;
103        }
104        mExecutor.shutdownNow();
105        if (!mExecutor.awaitTermination(AWAIT_TERMINATION_TIMEOUT, TimeUnit.MILLISECONDS)) {
106            Log.e(MtpDocumentsProvider.TAG, "Failed to terminate RootScanner's background thread.");
107        }
108        mExecutor = null;
109    }
110
111    /**
112     * Runnable to scan roots and update the database information.
113     */
114    private final class UpdateRootsRunnable implements Runnable {
115        final CountDownLatch mFirstScanCompleted = new CountDownLatch(1);
116
117        @Override
118        public void run() {
119            Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
120            int pollingCount = 0;
121            while (true) {
122                boolean changed = false;
123
124                // Update devices.
125                final MtpDeviceRecord[] devices = mManager.getDevices();
126                try {
127                    mDatabase.getMapper().startAddingDocuments(null /* parentDocumentId */);
128                    for (final MtpDeviceRecord device : devices) {
129                        if (mDatabase.getMapper().putDeviceDocument(device)) {
130                            changed = true;
131                        }
132                    }
133                    if (mDatabase.getMapper().stopAddingDocuments(
134                            null /* parentDocumentId */)) {
135                        changed = true;
136                    }
137                } catch (FileNotFoundException exception) {
138                    // The top root (ID is null) must exist always.
139                    // FileNotFoundException is unexpected.
140                    Log.e(MtpDocumentsProvider.TAG, "Unexpected FileNotFoundException", exception);
141                    throw new AssertionError("Unexpected exception for the top parent", exception);
142                }
143
144                // Update roots.
145                for (final MtpDeviceRecord device : devices) {
146                    final String documentId = mDatabase.getDocumentIdForDevice(device.deviceId);
147                    if (documentId == null) {
148                        continue;
149                    }
150                    try {
151                        mDatabase.getMapper().startAddingDocuments(documentId);
152                        if (mDatabase.getMapper().putStorageDocuments(
153                                documentId, device.eventsSupported, device.roots)) {
154                            changed = true;
155                        }
156                        if (mDatabase.getMapper().stopAddingDocuments(documentId)) {
157                            changed = true;
158                        }
159                    } catch (FileNotFoundException exception) {
160                        Log.e(MtpDocumentsProvider.TAG, "Parent document is gone.", exception);
161                        continue;
162                    }
163                }
164
165                if (changed) {
166                    notifyChange();
167                }
168                mFirstScanCompleted.countDown();
169                pollingCount++;
170                try {
171                    // Use SHORT_POLLING_PERIOD for the first SHORT_POLLING_TIMES because it is
172                    // more likely to add new root just after the device is added.
173                    // TODO: Use short interval only for a device that is just added.
174                    Thread.sleep(pollingCount > SHORT_POLLING_TIMES ?
175                        LONG_POLLING_INTERVAL : SHORT_POLLING_INTERVAL);
176                } catch (InterruptedException exp) {
177                    break;
178                }
179            }
180        }
181    }
182}
183