Question regarding lifetime of PRIV_TASK pointer
guillaume.quintard at gmail.com
Thu Mar 24 18:32:05 UTC 2022
Just to show off a bit, and because I know you have an eye on rust:
is the rust equivalent of vmod_priv and will properly be garbage-collected
when dropped (yes, I do need to write some docs for it!)
On Thu, Mar 24, 2022 at 6:46 AM Lee Hambley <lee.hambley at gmail.com> wrote:
> This is exaclty what we were looking for. Thank you sincerely.
> Lee Hambley
> +49 (0) 170 298 5667
> On Wed, 23 Mar 2022 at 17:15, Guillaume Quintard <
> guillaume.quintard at gmail.com> wrote:
>> Hi Lee,
>> Looks like you had the right page, but missed the interesting part :-) In
>> have this bit:
>> > .fini will be called for a non-NULL .priv of the struct vmod_priv when
>> the scope ends with that .priv pointer as its second argument besides a
>> i.e. if your vmod_priv has a methods->fini pointer, it will be called
>> when the vmod_priv is deleted.
>> Was this what you were after, or did I misunderstand your question?
>> Guillaume Quintard
>> On Wed, Mar 23, 2022 at 7:28 AM Lee Hambley <lee.hambley at gmail.com>
>>> Dear List,
>>> I inherited a project using PRIV_TASK  for which the documentation
>>> PRIV_TASK “per task” private pointers are useful for state that applies
>>> to calls for either a specific request or a backend request. For instance
>>> this can be the result of a parsed cookie specific to a client. Note that
>>> PRIV_TASK contexts are separate for the client side and the backend
>>> side, so use in vcl_backend_* will yield a different private pointer
>>> from the one used on the client side. These private pointers live only for
>>> the duration of their task.
>>> We do a form of reference counting in our internal data structures, and
>>> the PRIV_TASK pointer in parts is used to hold a (counted) reference to
>>> some data in the shared structure.
>>> We are struggling to find the latest possible safest place to hook where
>>> PRIV_TASK is about to be invalid (end of the request) so that we can
>>> safely, and finally decrement the reference count and clean-up.
>>> Writing this out now, I suspect that there's a safe exit from the state
>>> machine  where we could modify our VCL to include a call to a clean-up
>>> function in our vmod, however it's not clear to me if this would be "safe"
>>> (restarts, request coalescing, etc, etc)
>>> In short then, is there an obvious place into which we can hook which is
>>> the place where Varnish is already about to discard the "task" and it is
>>> unoquivically safe for us to decrement our reference counted pointer to the
>>> PRIV_TASK referenced data?
>>> Thanks so much, very much enjoying being in a role hacking on Varnish,
>>> and Varnish adjacent stuff in my job currently.
>>> Lee Hambley
>>> +49 (0) 170 298 5667
>>> varnish-misc mailing list
>>> varnish-misc at varnish-cache.org
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