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