Posted by Mitesh on 02/28/07 16:52

Tim Streater wrote:
> In article <1172668483.913253.134510@h3g2000cwc.googlegroups.com>,
> "Mitesh" <oopsbabies@hotmail.com> wrote:
>
> > Jerry Stuckle wrote:
> > > Michael Fesser wrote:
> > > > .oO(Jerry Stuckle)
> > > >
> > > >> Toby A Inkster wrote:
> > > >>
> > > >>> You have:
> > > >>>
> > > >>> $res = mysql_query("SELECT * FROM table1");
> > > >>> ...
> > > >>> $res = mysql_query("SELECT * FROM table2");
> > > >>> if(!$res)
> > > >>> return;
> > > >>>
> > > >>> $res is still going to be set as a result of your first query.
> > > >>>
> > > >>> Use unset($res) between each query.
> > > >> No, Toby.
> > > >>
> > > >> $res will have the results of the second query. The resource returned
> > > >> by the second query (or false) will overwrite what was in $res.
> > > >
> > > > Try that with PDO and it will crash most likely. Overwriting $res will
> > > > not necessarily free the previous result set, which might then lead to
> > > > MySQL complaining about an unbuffered query or something like that.
> > > >
> > > > | You cannot use the same variable for a PDOStatement object twice. As
> > > > | others have pointed out it works when you set this variable to null in
> > > > | between.
> > > >
> > > > http://bugs.php.net/bug.php?id=35793
> > > >
> > > > Micha
> > >
> > > We're not talking PDO , Micha.
> > >
> > > --
> > > ==================
> > > Remove the "x" from my email address
> > > Jerry Stuckle
> > > JDS Computer Training Corp.
> > > jstucklex@attglobal.net
> > > ==================
> >
> > Ok if we need to call, mysql_free_result for mysql resources doesn't
> > that mean every other type of resources bound this way to a variable
> > must have a freeing function that has to be called before the variable
> > can be re-used? So doesn't it coincide with what I am saying that
> > variables bound to resources when re-used may cause problems. (and
> > according to the others post the variables can be re-used if the
> > previously allocated resource is freed)
>
> My understanding was that, if you re-use $res without a call to
> mysql_free_result, it re-uses what $res is, which is a pointer to a
> result set, but doing that does *not* free up the space used by the
> result set. At least that's how it used to be. I don't know if they have
> improved the internals such that mysql_free_result is now a dummy call,
> or whether that is inherently impossible because mysql itself holds the
> result set.
>
> Perhaps a guru can enlighten us.
>
> -- tim

My concern is not if the previous resource is deallocated or not. I
don't have a huge result set returned. It will eventually be freed.

What I am really afraid is the working of my current resource pointed
to by $res which I have experienced to be not working occasionally as
I stated that my second fetch array function suceeds some times and
fails other times.

Can the following happen?

When I overwrite $res variable (whatever the variable maybe a pointer
or a reference). Suppose the garbage collector kicks in and finds that
the previous resource isn't owned by any variable and tries to free
it. When it tries to free, it accesses the $res variable. But now the
$res variable owns another resource i.e. my second mysql result set
and wrongly frees the second resource hence my second
mysql_fetch_array fails.

I am sure that I have read that in PHP variables that contain
resources are reference variables (similar to pointers) unlike other
variables like the $req variable storing a string. We can indded make
a variable act like a reference using an ampersand i think.

Yes it seems we need a guru here.

So my would be question to our guru is can we safely re-use variables
that are references?

Right now I resolved the situation using two different variable names
before I got the suggestion on using mysql_free_result. The product is
already shipped and it seems to be working.

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