add something to control glib log output

[felixbuenemann]

I'm not sure if this is a libvips or ruby-vips problem, but suppressing warnings by setting the VIPS_WARNING environment variable to 0 no longer works.

Instead every warning is printed with a complete backtrace:

VIPS-WARNING **: Incompatible type for "RichTIFFIPTC"; tag ignored
	from /Users/felix/.rvm/gems/ruby-2.4.1/gems/gobject-introspection-3.1.8/lib/gobject-introspection/loader.rb:576:in `block in define_method'
	from /Users/felix/.rvm/gems/ruby-2.4.1/gems/ruby-vips-1.0.6/lib/vips/call.rb:185:in `build'
	from /Users/felix/.rvm/gems/ruby-2.4.1/gems/ruby-vips-1.0.6/lib/vips/call.rb:253:in `invoke'
	from /Users/felix/.rvm/gems/ruby-2.4.1/gems/ruby-vips-1.0.6/lib/vips/call.rb:282:in `call_base'
	from /Users/felix/.rvm/gems/ruby-2.4.1/gems/ruby-vips-1.0.6/lib/vips/image.rb:632:in `write_to_file'
…

I'm using ruby-vips 1.0.6 and gobject-introspection 3.1.8 with vips 8.5.6 on ruby 2.4.1.

[felixbuenemann]

Oh, I guess it could be caused by jcupitt/libvips#544.

[jcupitt]

Hi Felix, yes, libvips is now using g_warning() for this stuff. I'll see if I can find a workaround. You're right, there should be some compat thing for this.

[jcupitt]

In C, you add:

        g_log_set_handler( "VIPS", G_LOG_LEVEL_WARNING, my_log_handler, NULL );

somewhere just after startup to direct all warning messages to my_log_handler, perhaps:

static void
my_log_handler( const gchar *log_domain, GLogLevelFlags log_level,
        const gchar *message, gpointer user_data )
{       
}

to print nothing.

I'm trying to find the equivalent for Ruby. The default handler installed by ruby-gnome2 is obviously to print a backtrack.

[jcupitt]

I can't get the obvious Ruby things to work :( so I added a hack to vips_init() in 8.5. It seems to work:

john@kiwi:~/try$ ./try254.rb  ~/pics/broken2.png
VIPS-WARNING **: Read Error
	from /home/john/packages/gems/gems/gobject-introspection-3.1.8/lib/gobject-introspection/loader.rb:576:in `block in define_method'
.... many, many lines of output trimmed
h = 11.0
s = 32.0
v = 178.0
john@kiwi:~/try$ export VIPS_WARNING=1
john@kiwi:~/try$ ./try254.rb  ~/pics/broken2.png
h = 11.0
s = 32.0
v = 178.0

[felixbuenemann]

I have done some experimenting with GLib::Log.cancel_handler and GLib::Log.set_handler, but so far all I achieved was resetting to the default handler, which does not print the backtrace using GLib::Log.cancel_handler. The set_handler installs the built-in handler for a given domain and log level, but I've yet to find out how to remove a handler, because the remove_handler method required a handler id, that I'm not sure how to obtain…

[felixbuenemann]

@jcupitt I don't think ruby-gnome2 currently provides an api for setting your own log handlers, so supporting the VIPS_WARNING and VIPS_INFO environment variables is probably the best idea.

It also makes sure existing programs keep working as expected when upgrading to libvips 8.5+.

[jcupitt]

Yes, I poked about in ruby-gnome2 as well and I couldn't find any working API for this :(

Hopefully the new ruby-vips can handle this in a better way.

[felixbuenemann]

Yeah, I've yet to try out the new ffi-based ruby-vips, but it's on my todo because it should save me a ton of build dependencies (gobject-introspection-dev pulls in half of x11 through cairo-dev).

[jcupitt]

Yes, it's much, much thinner, which should make it simpler to maintain and support.

It runs the specs in half the time, so there might be a modest speedup too.

[felixbuenemann]

I installed a version of libvips 8.5.7 with the patch from this gist and it seems to work fine.

Should we leave this issue open, until there is a better solution in ruby-vips?

[jcupitt]

Good idea. The new ruby-vips ought to have something for this too.

[jcupitt]

I've added something to pyvips to redirect libvips warnings to the standard Python logging module. It's a nice simple thing and seems to work well.

https://github.com/jcupitt/libvips/issues/715#issuecomment-324356680

How about doing the same for Ruby? Would a redirect to logger be OK?