enum e_future_error
{
    FUTURE_ERROR_CANCEL,
    FUTURE_ERROR_EXCEPTION,
    FUTURE_ERROR_TIMEOUT
};
struct promise;
struct future;
typedef void (*future_success_cb)(void * result, void * user);
typedef void (*future_failed_cb)(enum e_future_error err, const char * what, void * user);
typedef void (*promise_ctx_destroy_cb)(struct promise* p);

struct future* future_create(future_success_cb * cb_success, future_failed_cb * cb_failed,  void * user);

struct future* promise_to_future(struct promise* p);
struct promise* future_to_promise(struct future* f);