Re: Python inferior control

[Richard Ward <daedalusfall at gmail dot com>]

> On the 23rd of August 2009 Oguz Kayral submitted an initial patch to
> implement GDB inferior notification events in Python.

At the time I sent this (from a different email):

On 24 September 2009 02:52, Richard Ward <richard.j.ward1@googlemail.com> wrote:
> Oguz Kayral wrote:
>>
>> Hi,
>> This patch series adds inferior event handling support to GDB Python
>> scripting.
>
> Hi Oguz, I've been looking forward to this functionality, Good stuff!
>
> I have a few comments though, if you don't mind.
>
>
> Firstly two (fairly  unimportant) things about the function registration.
>
> I think it would be nice if you could give upvalues to the registration
> function (similar to gobject's `connect'), though admittedly it is very easy
> to fake that in python using a class that defines __call__.
>
> Also, I'm not sure whether this would ever be an issue but it seems
> advantageous to have the registration function return a unique object or
> number that could subsequently be used to unregister your callable, rather
> than using the callable object itself.
>
>
> Next, in python-stopevent.c:
> emit_stop_event (struct bpstats *bs, const char *stop_signal)
> {
>  /*...snip...*/
>  for (i = 0; i < PyList_Size (callback_list); i++)
>    {
>      PyObject_CallObject (PyList_GET_ITEM (callback_list, i), args_tuple);
>    }
> }
>
> A couple of issues with this. First, PyObject_Callback returns a new
> reference which is the return value of the function (or NULL), so it must be
> handled otherwise it will leak.
>
> Secondly the user code may throw an exception, or the object may not be
> callable. The exception should be cleared, and it would be nice to also
> print the exception (PyErr_Print does both).
>
> Most important here though is the iteration through the list. If the user
> disconnects a callback from inside a callback then the some callbacks could
> be skipped. It could be better to copy the list first, but that could still
> lead to some confusing behaviour, for example a callback being called after
> the user thinks it ought to have been disconnected.
>
> Thanks,
> Richard

I think on reflection that copying the list is probably the sensible way to go.