legacy Singleton threadsafe

threadSafeSingleton.kt

class SingletonThreadSafe private constructor() {
    companion object {
        private var _instance: SingletonThreadSafe? = null
        fun getInstance(): SingletonThreadSafe {
            val cachedInstance = _instance
            return cachedInstance ?: synchronized(this) {
                cachedInstance ?: SingletonThreadSafe().also {
                    _instance = it
                }
            }
        }
    }
}