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Re: PQisBusy() always busy

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: bradg <bg4all(at)me(dot)com>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: PQisBusy() always busy
Date: 2011-09-12 14:16:51
Message-ID: CAHyXU0wEAfHmZHiL7KS+BjXQ6u8vsNf3tXQMYfyfDqsx11uTCQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-novice
On Mon, Sep 12, 2011 at 6:16 AM, bradg <bg4all(at)me(dot)com> wrote:
> It seems like PQisBusy() == 1 indefinitely after calling the asynchronous
> function PQsendQueryParams().
>
> I am using a method to check for the availability of asynchronous results
> straight out of the latest PostgreSQL book by Korry and Susan Douglas. It
> uses select() and then FD_ISSET on the connection socket, then calls both
> PQconsumeInput() and PQisBusy().
>
> For some reason, the value for PQisBusy() is always 1, no matter how long I
> let the program run.
>
> I'm just wondering if anyone can point me in the right direction. For what
> it's worth. I'm programming in OS X 10.7 with Xcode 4.1 using the PostgreSQL
> files from the EnterpriseDB one-click installer.
>
> Here's the function:
>
> bool is_result_ready( PGconn * connection )
> {
>    int                 my_socket;
>    struct timeval      timer;
>    fd_set              read_mask;
>
>    if( PQisBusy( connection ) == FALSE )
>        return( TRUE );
>
>    my_socket = PQsocket( connection );
>
>    timer.tv_sec  = (time_t)1;
>    timer.tv_usec = 0;
>
>    FD_ZERO( &read_mask );
>    FD_SET( my_socket, &read_mask );
>
>    if( select( my_socket + 1, &read_mask, NULL, NULL, &timer ) == 0 )
>    {
>        return( FALSE );
>    }
>    else if( FD_ISSET( my_socket, &read_mask ))
>    {
>        PQconsumeInput( connection );
>
>        if( PQisBusy( connection ))    <------ THIS PQisBusy() ALWAYS
> RETURNS 1
>            return( FALSE );
>        else
>            return( TRUE );
>    }
>    else
>    {
>        return( FALSE );
>    }
> }
>
>
> Thanks in advance for any insight.

You are not checking the return of PQconsumeInput -- if there is a
problem with the connection, you won't catch the change to the
internal asyncStatus flag because it only gets changed from data
returned over the socket. Try changing your code to watch for
PQconsumeInput return value, and displaying/handling the connection
error if there is a problem.

per docs: "PQconsumeInput normally returns 1 indicating "no error",
but returns 0 if there was some kind of trouble (in which case
PQerrorMessage can be consulted). Note that the result does not say
whether any input data was actually collected. After calling
PQconsumeInput, the application can check PQisBusy and/or PQnotifies
to see if their state has changed."

merlin

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