SettingsProvider 之 FileObserver

转载请注明出处：http://blog.youkuaiyun.com/droyon/article/details/35558637

// FileObserver for external modifications to the database file.
    // Note that this is for platform developers only with
    // userdebug/eng builds who should be able to tinker with the
    // sqlite database out from under the SettingsProvider, which is
    // normally the exclusive owner of the database.  But we keep this
    // enabled all the time to minimize development-vs-user
    // differences in testing.
    //FileObserver是外部对数据库修改的监听。
    //这是userdebug或者eng版本的平台开发者，开发者也是独占数据库的所有者，能够在SettingsProvider中摆弄sqlite数据库。
    //这个监听，能够保持长久运行，减小开发者和用户之间的差距。
    private static SparseArray<SettingsFileObserver> sObserverInstances
            = new SparseArray<SettingsFileObserver>();
    private class SettingsFileObserver extends FileObserver {
        private final AtomicBoolean mIsDirty = new AtomicBoolean(false);
        private final int mUserHandle;
        private final String mPath;

        public SettingsFileObserver(int userHandle, String path) {
            super(path, FileObserver.CLOSE_WRITE |
                  FileObserver.CREATE | FileObserver.DELETE |
                  FileObserver.MOVED_TO | FileObserver.MODIFY);
            mUserHandle = userHandle;
            mPath = path;
        }

        public void onEvent(int event, String path) {
            int modsInFlight = sKnownMutationsInFlight.get(mUserHandle).get();
            if (modsInFlight > 0) {
                // our own modification.
                return;
            }
            Log.d(TAG, "User " + mUserHandle + " external modification to " + mPath
                    + "; event=" + event);
            if (!mIsDirty.compareAndSet(false, true)) {//isDirty为true，说明在进行fullyPopulateCaches，不需要在做。
                // already handled. (we get a few update events
                // during an sqlite write)
                return;
            }
            Log.d(TAG, "User " + mUserHandle + " updating our caches for " + mPath);
            fullyPopulateCaches(mUserHandle);
            mIsDirty.set(false);
        }
    }