Re: Infinite loop on error

On 8/2/10, Daniele Varrazzo <[email protected]> wrote:
> On Wed, Jul 28, 2010 at 4:54 PM, Marko Kreen <[email protected]> wrote:
>  > Psycopg has several loops in form:
>  >
>  > while ((curs->pgres = PQgetResult()) != NULL)
>  > {
>  > }
>  >
>  > or
>  >
>  > do {
>  >  pgres = PQgetResult();
>  > } while (pgres != NULL);
>  >
>  >
>  > The problem is that if libpq gets so fatal error it decides
>  > to close the connection, PQgetResult() will never return NULL
>  > from that connection, thus infinite loop.
>
>
> Are you sure about that? I don't have the libpq source code handy, I
>  will surely check that.

Yeah, found out via strace/gdb...  strace was showing infinite
close(-1) - thus libpq was trying to close already closed connection.

> But, if it doesn't return a NULL with the
>  connection in broken state... what does it return?

Probably PQmakeEmptyPGresult(conn, PGRES_FATAL_ERROR)

>  PQgetResult() also returns null when there is no result to fetch. I
>  may have extrapolated excessively assuming that it returns null when
>  the connection is closed too, but it doesn't seem an excessively
>  stretched interpretation.

Yeah, seems NULL means "query is finished _and_ everything is fine".

>  I'm curious to do some test in the next days.

Have fun.

-- 
marko