[pulseaudio-discuss] [patches] constification round #4 (pa_mainloop_api)

[Tanu Kaskinen]

On Thu, 2018-07-05 at 23:51 +0100, jnqnfe at gmail.com wrote:
> On Wed, 2018-07-04 at 11:46 +0300, Tanu Kaskinen wrote:
> > On Mon, 2018-07-02 at 17:58 +0100, jnqnfe at gmail.com wrote:
> > > On Fri, 2018-06-29 at 16:06 +0300, Tanu Kaskinen wrote:
> > > > On Thu, 2018-06-28 at 04:08 +0100, jnqnfe at gmail.com wrote:
> > > > > It's possible for patches #21, #23 and #24 to be bumped down
> > > > > before
> > > > > the
> > > > > API change of #20, but as things are they are blocked by it and
> > > > > it
> > > > > would require a temporary hack... #23 and #24 (utils) depend
> > > > > upon
> > > > > pa_signal_init(), done in #21 which involves changing the
> > > > > underlying
> > > > > static; this depends upon changing pa_signal_destroy_cb_t
> > > > > (#20),
> > > > > because of the way pa_signal_free() works (passing that static
> > > > > api
> > > > > ref
> > > > > to the destroy callback which requires non-const). Getting
> > > > > around
> > > > > this
> > > > > would require injecting a temporary hack into pa_signal_free()
> > > > > giving
> > > > > alternate means of obtaining a non-const api pointer - i.e. api
> > > > > function pointer comparison would be necessary to tell us which
> > > > > mainloop is in use, to then get what we need using the correct
> > > > > *_get_api() with api->userdata.
> > > > 
> > > > We can't change the signatures of publicly declared callback
> > > > types.
> > > > That will cause incompatibilities (compiler warnings at least,
> > > > which
> > > > is
> > > > bad enough) in applications.
> > > 
> > > Sure
> > > 
> > > > Therefore the only patch that I could
> > > > apply is the first one.
> > > 
> > > But the types aren't changed until #19/26 ...
> > 
> > Patch 4 changes the callback signatures.
> 
> Right, but only in the mainloop api vtable, which user's only read
> values from, so I wasn't expecting that to be an issue.

Applications can also write to it, if they implement their own
mainloops.

When I wrote my previous mail, I thought that patch 4 also changes the
event callback types (pa_io_event_cb_t etc.), and that was what I was
primarily concerned about (but applications implementing their own
mainloops is still a real problem). I can't now find the patch that
changes the callback types, but there are many patches that change the
callback implementation signatures, and if there's no corresponding
change to the callback types, that causes warnings (for example, try
applying patch 2 alone, and you'll get warnings when building
pulseaudio).

-- 
Tanu

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