void mbedtls_threading_set_alt(void(*mutex_init)(mbedtls_threading_mutex_t *), void(*mutex_free)(mbedtls_threading_mutex_t *), int(*mutex_lock)(mbedtls_threading_mutex_t *), int(*mutex_unlock)(mbedtls_threading_mutex_t *))
Set your alternate threading implementation function pointers and initialize global mutexes...