Method ~CachedReader

src/bvar/default_variables.cpp:141–143

        CHECK_EQ(0, pthread_mutex_init(&_mutex, NULL));
    }
    ~CachedReader() {
        pthread_mutex_destroy(&_mutex);
    }

    // NOTE: may return a volatile value that may be overwritten at any time.
    // This is acceptable right now. Both 32-bit and 64-bit numbers are atomic