Re: Infinite loop on error

On Mon, Aug 2, 2010 at 7:56 AM, Marko Kreen <markokr@...> wrote:
> On 8/2/10, Daniele Varrazzo <daniele.varrazzo@...> wrote:
>> On Wed, Jul 28, 2010 at 4:54 PM, Marko Kreen <markokr@...> wrote:
>>  > Psycopg has several loops in form:
>> [...]
>>  > 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)

Yup, seen in the libpq source.

>>  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 shall propose a clarification to the pg docs ml.