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/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import android.annotation.Nullable;
import android.util.Log;
import java.lang.ref.WeakReference;
import java.util.HashMap;
/**
* Monitors files (using <a href="http://en.wikipedia.org/wiki/Inotify">inotify</a>)
* to fire an event after files are accessed or changed by by any process on
* the device (including this one). FileObserver is an abstract class;
* subclasses must implement the event handler {@link #onEvent(int, String)}.
*
* <p>Each FileObserver instance monitors a single file or directory.
* If a directory is monitored, events will be triggered for all files and
* subdirectories inside the monitored directory.</p>
*
* <p>An event mask is used to specify which changes or actions to report.
* Event type constants are used to describe the possible changes in the
* event mask as well as what actually happened in event callbacks.</p>
*
* <p class="caution"><b>Warning</b>: If a FileObserver is garbage collected, it
* will stop sending events. To ensure you keep receiving events, you must
* keep a reference to the FileObserver instance from some other live object.</p>
*/
public abstract class FileObserver {
/** Event type: Data was read from a file */
public static final int ACCESS = 0x00000001;
/** Event type: Data was written to a file */
public static final int MODIFY = 0x00000002;
/** Event type: Metadata (permissions, owner, timestamp) was changed explicitly */
public static final int ATTRIB = 0x00000004;
/** Event type: Someone had a file or directory open for writing, and closed it */
public static final int CLOSE_WRITE = 0x00000008;
/** Event type: Someone had a file or directory open read-only, and closed it */
public static final int CLOSE_NOWRITE = 0x00000010;
/** Event type: A file or directory was opened */
public static final int OPEN = 0x00000020;
/** Event type: A file or subdirectory was moved from the monitored directory */
public static final int MOVED_FROM = 0x00000040;
/** Event type: A file or subdirectory was moved to the monitored directory */
public static final int MOVED_TO = 0x00000080;
/** Event type: A new file or subdirectory was created under the monitored directory */
public static final int CREATE = 0x00000100;
/** Event type: A file was deleted from the monitored directory */
public static final int DELETE = 0x00000200;
/** Event type: The monitored file or directory was deleted; monitoring effectively stops */
public static final int DELETE_SELF = 0x00000400;
/** Event type: The monitored file or directory was moved; monitoring continues */
public static final int MOVE_SELF = 0x00000800;
/** Event mask: All valid event types, combined */
public static final int ALL_EVENTS = ACCESS | MODIFY | ATTRIB | CLOSE_WRITE
| CLOSE_NOWRITE | OPEN | MOVED_FROM | MOVED_TO | DELETE | CREATE
| DELETE_SELF | MOVE_SELF;
private static final String LOG_TAG = "FileObserver";
private static class ObserverThread extends Thread {
private HashMap<Integer, WeakReference> m_observers = new HashMap<Integer, WeakReference>();
private int m_fd;
public ObserverThread() {
super("FileObserver");
m_fd = init();
}
public void run() {
observe(m_fd);
}
public int startWatching(String path, int mask, FileObserver observer) {
int wfd = startWatching(m_fd, path, mask);
Integer i = new Integer(wfd);
if (wfd >= 0) {
synchronized (m_observers) {
m_observers.put(i, new WeakReference(observer));
}
}
return i;
}
public void stopWatching(int descriptor) {
stopWatching(m_fd, descriptor);
}
public void onEvent(int wfd, int mask, String path) {
// look up our observer, fixing up the map if necessary...
FileObserver observer = null;
synchronized (m_observers) {
WeakReference weak = m_observers.get(wfd);
if (weak != null) { // can happen with lots of events from a dead wfd
observer = (FileObserver) weak.get();
if (observer == null) {
m_observers.remove(wfd);
}
}
}
// ...then call out to the observer without the sync lock held
if (observer != null) {
try {
observer.onEvent(mask, path);
} catch (Throwable throwable) {
Log.wtf(LOG_TAG, "Unhandled exception in FileObserver " + observer, throwable);
}
}
}
private native int init();
private native void observe(int fd);
private native int startWatching(int fd, String path, int mask);
private native void stopWatching(int fd, int wfd);
}
private static ObserverThread s_observerThread;
static {
s_observerThread = new ObserverThread();
s_observerThread.start();
}
// instance
private String m_path;
private Integer m_descriptor;
private int m_mask;
/**
* Equivalent to FileObserver(path, FileObserver.ALL_EVENTS).
*/
public FileObserver(String path) {
this(path, ALL_EVENTS);
}
/**
* Create a new file observer for a certain file or directory.
* Monitoring does not start on creation! You must call
* {@link #startWatching()} before you will receive events.
*
* @param path The file or directory to monitor
* @param mask The event or events (added together) to watch for
*/
public FileObserver(String path, int mask) {
m_path = path;
m_mask = mask;
m_descriptor = -1;
}
protected void finalize() {
stopWatching();
}
/**
* Start watching for events. The monitored file or directory must exist at
* this time, or else no events will be reported (even if it appears later).
* If monitoring is already started, this call has no effect.
*/
public void startWatching() {
if (m_descriptor < 0) {
m_descriptor = s_observerThread.startWatching(m_path, m_mask, this);
}
}
/**
* Stop watching for events. Some events may be in process, so events
* may continue to be reported even after this method completes. If
* monitoring is already stopped, this call has no effect.
*/
public void stopWatching() {
if (m_descriptor >= 0) {
s_observerThread.stopWatching(m_descriptor);
m_descriptor = -1;
}
}
/**
* The event handler, which must be implemented by subclasses.
*
* <p class="note">This method is invoked on a special FileObserver thread.
* It runs independently of any threads, so take care to use appropriate
* synchronization! Consider using {@link Handler#post(Runnable)} to shift
* event handling work to the main thread to avoid concurrency problems.</p>
*
* <p>Event handlers must not throw exceptions.</p>
*
* @param event The type of event which happened
* @param path The path, relative to the main monitored file or directory,
* of the file or directory which triggered the event. This value can
* be {@code null} for certain events, such as {@link #MOVE_SELF}.
*/
public abstract void onEvent(int event, @Nullable String path);
}
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