PQisBusy behaving strangely

Hi All,

Not sure if this is the right pgsql-* "channel" to post to, but I was
hoping maybe someone could answer a question from one of my fellow
developers.  Please read below:

> So, following the documentation, we wrote a little ASYNC version of
> exec. here is the code:
>
> PGresult *PGClient::exec(char *query) {
>  PGresult *result;
>
>  if (conn == NULL) {
>    ERROR("PGClient calling exec when a connection hasn't been
> established yet");
>    return NULL;
>  }
>  if (PQsendQuery(conn,query)==0) {
>    ERROR("PGClient wasn't able to sendQuery");
>    return NULL;
>  }
>  int socketFD = PQsocket(conn);
>  pollfd pfd;
>  pfd.fd = socketFD;
>  pfd.events = POLLIN|POLLRDHUP;
> consumeSome:
>  if (poll(&pfd,1,PG_EXEC_TIMEOUT*1000) == 0) {
>    ERROR("PGClient is timing out ");
>    return NULL;
>  }
>  if (PQconsumeInput(conn)==0) {
>    ERROR("PGClient detected trouble when trying to consumeInput");
>    return NULL;
>  }
>  if (PQisBusy(conn))
>    goto consumeSome;
>  result = PQgetResult(conn);
>  if (PQisBusy(conn)) {
>    // something is wrong, because this is telling us that there is
> more data on the way,
> but there shouldn't be.
>    ERROR("PGClient had a weird case where more data is on its way");
>  }
>  PGresult *tempResult=PQgetResult(conn);
>  if (tempResult!=0) {
>    // we either had multiple SQL queries that return multiple
> results or something weird
> happened here, caller should close connection
>    ERROR("PGClient had a weird case where multiple results were
> returned");
>  }
>  return result;
> }
>
> So, assuming that every query we pass in is just a simple, 1 result-
> set-returning query, we should never see PQisBusy returning a non-
> NULL after we do the PQgetResult. BUT every now and then, in our
> code, the PQisBusy function returns a non-NULL and we get that
> ERROR("PGClient had a weird case where more data is on its way")...
> BUT when we do tempResult=PQgetResult, then it is ALWAYS null... can
> someone please explain how PQisBusy can return true (when we aren't
> expecting it to) but then PQgetResult returns nothing?

If there's any knowledge of why PQisBusy returns not-null, yet nothign
comes our of PQgetResult, could you let me know what's going on?

Any help much appreciated!
--Richard