Implementing A "Future" (Cont.)

The method used when waiting for a value to be set:

/* wait for the value of the given future to be set. */
/* returns '0' on success, '-1' on error.            */
/* if success, stores the value in '*value'.         */
/* on failure, 'errno' is set to 'EAGAIN' if there   */
/* was a timeout.                                    */
int int_future_wait_for_value(struct int_future* f, int* value)
{
  int rc = -1; /* assume failure. */

  if (!f || !value) {
    errno = EINVAL;
    goto int_future_wait_for_value_ret;
  }