[vlc-devel] [PATCH 1/2] libvlc: added a formatted log callback

[Thomas Guillem]

On Sat, May 18, 2019, at 09:29, Rémi Denis-Courmont wrote:
> Le perjantaina 17. toukokuuta 2019, 11.05.00 EEST Jérémy VIGNELLES a écrit :
> > ---
> >  include/vlc/libvlc.h | 64 ++++++++++++++++++++++++++++++++++++++++++++
> >  lib/libvlc.sym       |  3 +++
> >  lib/log.c            | 55 +++++++++++++++++++++++++++++++++++++
> >  3 files changed, 122 insertions(+)
> > 
> > diff --git a/include/vlc/libvlc.h b/include/vlc/libvlc.h
> > index 1c2550fe3b..1b21c2da66 100644
> > --- a/include/vlc/libvlc.h
> > +++ b/include/vlc/libvlc.h
> > @@ -433,6 +433,26 @@ LIBVLC_API void libvlc_log_get_object(const
> > libvlc_log_t *ctx, typedef void (*libvlc_log_cb)(void *data, int level,
> > const libvlc_log_t *ctx, const char *fmt, va_list args);
> > 
> > +/**
> > + * Callback prototype for LibVLC preformatted log message handler.
> > + *
> > + * \param data data pointer as given to libvlc_log_set()
> > + * \param level message level (@ref libvlc_log_level)
> > + * \param ctx message context (meta-information about the message)
> > + * \param message the message, already formatted
> > + * \note Log message handlers <b>must</b> be thread-safe.
> > + * \warning The message context pointer, and the message string parameters
> > + *          are only valid until the callback returns.
> > + */
> > +typedef void (*libvlc_log_preformatted_cb)(void *data, int level, const
> > libvlc_log_t *ctx, +                              const char *message);
> 
> There is no logic there. Many languages will either not support callbacks at 
> all, or have no ways to make them thread safe, or will be unable to marshall 
> pointers from callbacks, etc.
> 
> And the libvlc_log_t is definitely not supported in higher level languages, 
> neither are many other compound types. In fact, even 'int' is iffy, since 
> typically only fixed-size types are handeld.
> 
> We *used* to have a log API that was "easy" to call from other languages. We 
> removed it because it was so incredibly broken and intrinsically unfixable.
> 
> LibVLC is not, or rather no longer for a decade or so, meant to be called 
> directly from foreign interfaces.

I completely disagree. You should not decide that alone. 

> 
> -- 
> Rémi Denis-Courmont
> http://www.remlab.net/
> 
> 
> 
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