Re: Asynchronous interface help?

Hello Adam,

Sorry for the late reply, Christmas and all that...

I notice in your code snippet that the call to 'select()' is:

>     retval = select(1, &rfds, NULL, NULL, &tv);

Well, the 1st parameter to select is the highest file descriptor in any of
the fd sets + 1 NOT the number of file descriptors to check.  What you're
saying here is check fd 0 (1 == 0 + 1) which is 'stdin' !  Not what you're
after I believe?  To check your connection's socket you need:
select(PQsocket(pgsql) + 1, &rfds, NULL, NULL, &tv);

as the 1st parameter.  This gives the socket fd number + 1!

Hope this helps.


Paul M. Breen, Software Engineer - Computer Park Ltd.

Tel:   (01536) 417155
Email: pbreen@computerpark.co.uk

On Tue, 2 Jan 2001, Adam Haberlach wrote:

> I'm working on using PostgreSQL to synchronize two seperate web connections
> for some silly authentication reasons.  I'm adding a method to PHP that will
> allow the generation of a page to wait on a named notify from another
> backend process.  It doesn't seem to work correctly.  Here's the abridged
> version of the code...
> 
> PHP_FUNCTION(pg_wait) {
>     zval **timeout, **pgsql_link;
>     int id = -1;
>     fd_set rfds;
>     int retval;
>     PGconn *pgsql;
>     PGnotify *notify;
>     struct timeval tv;
>     char *buf;
>     int nbytes;
>     int trycount=0;
> 
>     /* ... */
> 
>     ZEND_FETCH_RESOURCE2(pgsql, PGconn *, pgsql_link, id, "PostgreSQL link", le_link, le_plink);
>     convert_to_long_ex(timeout);
> 
>     FD_ZERO(&rfds);
>     FD_SET(PQsocket(pgsql), &rfds);
> 
>     tv.tv_sec = Z_STRVAL_PP(timeout);
>     tv.tv_usec = 0;
> 
>     retval = select(1, &rfds, NULL, NULL, &tv);
>     if(retval) {
>         PQconsumeInput(pgsql);
>         notify = PQnotifies(pgsql);
>         if(notify) {
>             nbytes = strlen(notify->relname)+1;
>             buf = emalloc(nbytes);
>             memcpy(buf, notify->relname, nbytes);
>             free(notify);
> 
>         /* ... */
> 
>         }
>     } else {
>         printf("Timed out.  Socket==%d\n", PQsocket(pgsql));
>         RETURN_FALSE;
>     }
> 
> This always seems to time out.  Is there some mode that I need to put
> the backend into in order to make the socket valid?  I'm getting a
> non-stdio/stdout/stderr value back from PQsocket, so things can't be
> too messed up.
> 
> The following code seems to work, but polls--we would much rather
> block on select().
> 
>     while(trycount < Z_STRVAL_PP(timeout)) {
>         PQconsumeInput(pgsql);
>         notify = PQnotifies(pgsql);
>         if(notify) {
>             nbytes = strlen(notify->relname)+1;
>             buf = emalloc(nbytes);
>             memcpy(buf, notify->relname, nbytes);
>             free(notify);
> 
>         /* ... */
>         }
>         sleep(1);
>         trycount++;
>     }
> 
> 
> Anyone have any ideas?
> 
> -- 
> Adam Haberlach            |A cat spends her life conflicted between a
> adam@newsnipple.com       |deep, passionate, and profound desire for
> http://www.newsnipple.com |fish and an equally deep, passionate, and
> '88 EX500                 |profound desire to avoid getting wet.
>