enum e_future_error
{
    FUTURE_ERROR_CANCEL
    FUTURE_ERROR_EXCEPTION,
    FUTURE_ERROR_TIMEOUT
}

typedef void (*future_cb_success_t)(void * result, void * user);
typedef void (*future_cb_failed_t)(enum e_future_error err, const char * what, void * user);

struct future
{
    void * user;
    future_cb_success_t * cb_success;
    future_cb_failed_t * cb_failed;
};

struct promise
{
    struct future f;
    void * ctx;
}

typedef void * promise_t;
void future_cancel(struct future * future)
{
    future->cancel();
}

void promise_success(struct promisc *, void * result);
void promise_fail();

struct future *  XXXXXRpc()
{
    cancel = ___XXXXCancel()
};