Double-checked locking

FileBaseProvider.cs

        private static FileSystemWatcherPool sInstance;
        private static object sLock = new object();

        private FileSystemWatcherPool() {
            this.cleanupTimer = new Timer(InvalidateWatcherList, null, OneMinute, OneMinute);
        }

        public static FileSystemWatcherPool Instance {
            get {
                if (sInstance == null) {
                    lock (sLock) {
                        if (sInstance == null) {
                            sInstance = new FileSystemWatcherPool();
                        }
                    }
                }
                return sInstance;
            }
        }