1/*
2 * Copyright (C) 2006 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 android.os;
18
19import android.util.Log;
20
21import com.android.internal.os.RuntimeInit;
22
23import java.lang.ref.WeakReference;
24import java.util.ArrayList;
25import java.util.HashMap;
26
27/**
28 * Monitors files (using <a href="http://en.wikipedia.org/wiki/Inotify">inotify</a>)
29 * to fire an event after files are accessed or changed by by any process on
30 * the device (including this one).  FileObserver is an abstract class;
31 * subclasses must implement the event handler {@link #onEvent(int, String)}.
32 *
33 * <p>Each FileObserver instance monitors a single file or directory.
34 * If a directory is monitored, events will be triggered for all files and
35 * subdirectories (recursively) inside the monitored directory.</p>
36 *
37 * <p>An event mask is used to specify which changes or actions to report.
38 * Event type constants are used to describe the possible changes in the
39 * event mask as well as what actually happened in event callbacks.</p>
40 *
41 * <p class="caution"><b>Warning</b>: If a FileObserver is garbage collected, it
42 * will stop sending events.  To ensure you keep receiving events, you must
43 * keep a reference to the FileObserver instance from some other live object.</p>
44 */
45public abstract class FileObserver {
46    /** Event type: Data was read from a file */
47    public static final int ACCESS = 0x00000001;
48    /** Event type: Data was written to a file */
49    public static final int MODIFY = 0x00000002;
50    /** Event type: Metadata (permissions, owner, timestamp) was changed explicitly */
51    public static final int ATTRIB = 0x00000004;
52    /** Event type: Someone had a file or directory open for writing, and closed it */
53    public static final int CLOSE_WRITE = 0x00000008;
54    /** Event type: Someone had a file or directory open read-only, and closed it */
55    public static final int CLOSE_NOWRITE = 0x00000010;
56    /** Event type: A file or directory was opened */
57    public static final int OPEN = 0x00000020;
58    /** Event type: A file or subdirectory was moved from the monitored directory */
59    public static final int MOVED_FROM = 0x00000040;
60    /** Event type: A file or subdirectory was moved to the monitored directory */
61    public static final int MOVED_TO = 0x00000080;
62    /** Event type: A new file or subdirectory was created under the monitored directory */
63    public static final int CREATE = 0x00000100;
64    /** Event type: A file was deleted from the monitored directory */
65    public static final int DELETE = 0x00000200;
66    /** Event type: The monitored file or directory was deleted; monitoring effectively stops */
67    public static final int DELETE_SELF = 0x00000400;
68    /** Event type: The monitored file or directory was moved; monitoring continues */
69    public static final int MOVE_SELF = 0x00000800;
70
71    /** Event mask: All valid event types, combined */
72    public static final int ALL_EVENTS = ACCESS | MODIFY | ATTRIB | CLOSE_WRITE
73            | CLOSE_NOWRITE | OPEN | MOVED_FROM | MOVED_TO | DELETE | CREATE
74            | DELETE_SELF | MOVE_SELF;
75
76    private static final String LOG_TAG = "FileObserver";
77
78    private static class ObserverThread extends Thread {
79        private HashMap<Integer, WeakReference> m_observers = new HashMap<Integer, WeakReference>();
80        private int m_fd;
81
82        public ObserverThread() {
83            super("FileObserver");
84            m_fd = init();
85        }
86
87        public void run() {
88            observe(m_fd);
89        }
90
91        public int startWatching(String path, int mask, FileObserver observer) {
92            int wfd = startWatching(m_fd, path, mask);
93
94            Integer i = new Integer(wfd);
95            if (wfd >= 0) {
96                synchronized (m_observers) {
97                    m_observers.put(i, new WeakReference(observer));
98                }
99            }
100
101            return i;
102        }
103
104        public void stopWatching(int descriptor) {
105            stopWatching(m_fd, descriptor);
106        }
107
108        public void onEvent(int wfd, int mask, String path) {
109            // look up our observer, fixing up the map if necessary...
110            FileObserver observer = null;
111
112            synchronized (m_observers) {
113                WeakReference weak = m_observers.get(wfd);
114                if (weak != null) {  // can happen with lots of events from a dead wfd
115                    observer = (FileObserver) weak.get();
116                    if (observer == null) {
117                        m_observers.remove(wfd);
118                    }
119                }
120            }
121
122            // ...then call out to the observer without the sync lock held
123            if (observer != null) {
124                try {
125                    observer.onEvent(mask, path);
126                } catch (Throwable throwable) {
127                    Log.wtf(LOG_TAG, "Unhandled exception in FileObserver " + observer, throwable);
128                }
129            }
130        }
131
132        private native int init();
133        private native void observe(int fd);
134        private native int startWatching(int fd, String path, int mask);
135        private native void stopWatching(int fd, int wfd);
136    }
137
138    private static ObserverThread s_observerThread;
139
140    static {
141        s_observerThread = new ObserverThread();
142        s_observerThread.start();
143    }
144
145    // instance
146    private String m_path;
147    private Integer m_descriptor;
148    private int m_mask;
149
150    /**
151     * Equivalent to FileObserver(path, FileObserver.ALL_EVENTS).
152     */
153    public FileObserver(String path) {
154        this(path, ALL_EVENTS);
155    }
156
157    /**
158     * Create a new file observer for a certain file or directory.
159     * Monitoring does not start on creation!  You must call
160     * {@link #startWatching()} before you will receive events.
161     *
162     * @param path The file or directory to monitor
163     * @param mask The event or events (added together) to watch for
164     */
165    public FileObserver(String path, int mask) {
166        m_path = path;
167        m_mask = mask;
168        m_descriptor = -1;
169    }
170
171    protected void finalize() {
172        stopWatching();
173    }
174
175    /**
176     * Start watching for events.  The monitored file or directory must exist at
177     * this time, or else no events will be reported (even if it appears later).
178     * If monitoring is already started, this call has no effect.
179     */
180    public void startWatching() {
181        if (m_descriptor < 0) {
182            m_descriptor = s_observerThread.startWatching(m_path, m_mask, this);
183        }
184    }
185
186    /**
187     * Stop watching for events.  Some events may be in process, so events
188     * may continue to be reported even after this method completes.  If
189     * monitoring is already stopped, this call has no effect.
190     */
191    public void stopWatching() {
192        if (m_descriptor >= 0) {
193            s_observerThread.stopWatching(m_descriptor);
194            m_descriptor = -1;
195        }
196    }
197
198    /**
199     * The event handler, which must be implemented by subclasses.
200     *
201     * <p class="note">This method is invoked on a special FileObserver thread.
202     * It runs independently of any threads, so take care to use appropriate
203     * synchronization!  Consider using {@link Handler#post(Runnable)} to shift
204     * event handling work to the main thread to avoid concurrency problems.</p>
205     *
206     * <p>Event handlers must not throw exceptions.</p>
207     *
208     * @param event The type of event which happened
209     * @param path The path, relative to the main monitored file or directory,
210     *     of the file or directory which triggered the event
211     */
212    public abstract void onEvent(int event, String path);
213}
214