[PATCH 1/3] Make default log handler print to stderr

[Kristian Høgsberg]

On Sat, Feb 08, 2014 at 11:44:11AM +0200, Pekka Paalanen wrote:
> On Fri,  7 Feb 2014 22:27:00 -0800
> Kristian Høgsberg <krh at bitplanet.net> wrote:
> 
> > On the client side we log fatal errors before we exit.  If a
> > client doesn't set a log handler, it's hard to figure out what
> > goes wrong. ---
> >  src/wayland-util.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/wayland-util.c b/src/wayland-util.c
> > index 4fe9c81..b099882 100644
> > --- a/src/wayland-util.c
> > +++ b/src/wayland-util.c
> > @@ -23,6 +23,7 @@
> >  
> >  #include <stdlib.h>
> >  #include <stdint.h>
> > +#include <stdio.h>
> >  #include <string.h>
> >  #include <stdarg.h>
> >  
> > @@ -361,11 +362,12 @@ wl_map_for_each(struct wl_map *map,
> > wl_iterator_func_t func, void *data) }
> >  
> >  static void
> > -wl_log_noop_handler(const char *fmt, va_list arg)
> > +wl_log_stderr_handler(const char *fmt, va_list arg)
> >  {
> > +	vfprintf(stderr, fmt, arg);
> >  }
> >  
> > -wl_log_func_t wl_log_handler = wl_log_noop_handler;
> > +wl_log_func_t wl_log_handler = wl_log_stderr_handler;
> >  
> >  void
> >  wl_log(const char *fmt, ...)
> > -- 
> 
> Hi,
> 
> seems you think it is fine to printf() from libwayland-client *and*
> libwayland-server by default, so ok by me then. You probably know
> library conventions better than I do.

I don't think our default behavior of silently ignoring fatal errors and
relying on the application to catch errors is fine.

The background for these three patches was that I ported simple-egl to
xdg-shell and forgot the call to set_unstable_version().  Without this,
weston sends an error in response to all other xdg-shell requests.
simple-egl doesn't set a log function, so this was never printed.
On top of that simple-egl calls wl_display_dispatch_pending() without
error checking so the fatal error didn't halt the loop and simple-egl
eventually crashed with a protocol buffer overflow.

That's a pretty unhelpful way to deal with errors and it took me a while
to get to the bottom of it.  Maybe we need a configurable error handler
instead, and then make the default handler print the error and abort.

The third patch in this series deals with the case where an application
doesn't dispatch the default queue for a long time (I've seen games that
have a thread that updates a progress bar/loading screen while the main
thread compiles shaders or such).  If an error occurs in that case we still
need to make sure we handle it. wl_display is thread safe so we can grab
the lock and dispatch wl_display events from any thread the calls into
dispatch.  This applies to error but it's also important for delete_id
events, to make sure the rendering thread recycles IDs.

> Thanks,
> pq