On Thu, Feb 03, 2005 at 03:49:11PM -0800, David Wheeler wrote:
> On Feb 3, 2005, at 3:30 PM, Tim Bunce wrote:
>
> >>Should be pretty straight-forward. Are there other events for which
> >>you'd like to add callbacks? OnPrepare, perhaps? OnExecute? OnFetch?
> >
> >Yes, but let's just start with the connect ones for now.
>
> Okay. It seems pretty simple. Your initial implementation is quite
> straight-forward:
>
> if ($dbh and my $oc = $dbh->{OnConnect}) {
> $oc->($dbh, $dsn, $user, $pass, $attr) if ref $oc eq 'CODE';
> }
>
> The only issue I can think of is that some callbacks will be called
> much more than others. Do you think that it's a performance issue to be
> checking for a callback every time the method is called when most
> people won't use it at all? I don't think I see a way around that,
> though...
One way I'd had in the back of my mind way to use the DBI dispatcher
to fire the callbacks.
$h->{Callbacks}->{$method_name} = \&foo; # called on entry
$h->{Callbacks}->{$method_name} = [ \&foo, \&bar ]; # foo on entry, bar on
exit
$h->{Callbacks}->{$method_name} = [ [EMAIL PROTECTED], \&bar ]; # each of
@subrefs on entry, bar on exit
that way _every_ method would get pre and post call hooks for free.
If a handle has no callbacks the cost would be unmeasurable (just
a bit flag test in the dispatcher). If a handle has any callbacks
then the added cost for calling a method that doesn't have a callback
would just be one hash lookup.
How's your C coding? :)
This approach doesn't directly support callbacks that need to fire
_within_ a method, such as the proposed OnConnectCached firing only
if connect_cached() does _not_ need to call connect().
[For that case you could have an pre-connect_cached callback that
temporarily installs a connect callback which sets a flag, and a
post-connect_cached callback that resets %$attr if the flag's not set.
But that's getting quite baroque!]
Alternatively connect_cached() could call a new method in that
situation and the hooks could be applied to that. But that's
relatively expensive and it would be 'odd' for that method to be
called with the $attr that was passed to connect_cached().
Alternatively some pseudo-method-names could be supported in the
$h->{Callbacks} hash (ie "connect_cached.reused") and the relevant
methods could check for and call them directly. Then the extra code
in connect_cached would something like this:
if (my $cb = $dbh->{Callbacks}) {
my $oc = $cb->{"connect_cached.reused"};
$oc->($dbh, $dsn, $user, $pass, $attr) if ref $oc eq 'CODE';
}
Umm, food for thought...
Tim.
