Avoid double messaging on subset creation

[astrofrog]

Avoid broadcasting a create subset message with an empty subset state followed by an update message, instead just broadcast a create subset message with the correct subset state

[astrofrog]

@dhomeier - would you like to review this? I've had confirmation from the jdaviz side that it works for them.

[rosteen]

Actually, maybe hold off on merging - I think we might need a small PR in Jdaviz, I'm seeing spectral extraction fail to extract when a spatial subset is created. Hopefully a quick fix on our end.

[dhomeier]

But nothing needed on this side, is that right?

[rosteen]

But nothing needed on this side, is that right?

I'm pretty sure that's correct, still investigating the fix on our end.

[rosteen]

@astrofrog It seems like at the point we get the SubsetCreate message, the subset hasn't finished propagating/being applied to all of the data - when I switched to subscribing to SubsetCreate for spectral extraction line 441 in spectral_extraction.py is causing our automatic extraction upon making a subset to fail:

uncertainties = uncert_cube.get_subset_object(
                        subset_id=aperture.selected, cls=StdDevUncertainty
                    )

with the error

File [~/projects/glue/glue/core/data.py:330](http://localhost:8888/lab/tree/~/projects/glue/glue/core/data.py#line=329), in BaseData.get_subset_object(self, subset_id, cls, **kwargs)
    326         raise ValueError('Specify the object class to use with cls= - supported '
    327                          'classes are:' + format_choices(data_translator.supported_classes))
    329 if len(self.subsets) == 0:
--> 330     raise ValueError("Dataset does not contain any subsets")
    331 elif subset_id is None:
    332     if len(self.subsets) == 1:

ValueError: Dataset does not contain any subsets

It seems like this is a timing conflict, would it be possible to send the SubsetCreate message after the subset has propagated to all of the relevant data? Or do you have a workaround you could recommend on our side?

[dhomeier]

The setter is already calling self._broadcast() afaics; any ideas if adding something in BaseData.add_subset could help?

[dhomeier]

Suggested change

	assert message.subset.subset_state.right == 3
	assert message.subset.subset_state.right == 3
	def test_broadcast_to_collection():
	"""A data collection input works on each data component"""
	handler = MagicMock()
	app = Application()
	class Listener(HubListener):
	pass
	listener = Listener()
	app.session.hub.subscribe(listener, SubsetCreateMessage, handler=handler)
	app.session.hub.subscribe(listener, SubsetUpdateMessage, handler=handler)
	data = Data(x=[1, 2, 3, 4, 5])
	data2 = Data(x=[2, 3, 4, 5, 6])
	app.data_collection.append(data)
	app.data_collection.append(data2)
	cmd = ApplySubsetState(data_collection=app.data_collection,
	subset_state=data.id['x'] >= 3,
	override_mode=ReplaceMode)
	app.session.command_stack.do(cmd)
	assert len(data2.subsets) == 1
	assert data2.subsets[0].label == 'Subset 1'
	# fails with `IncompatibleAttribute` exception
	# assert data2.get_subset_object(subset_id='Subset 1', cls=NDDataArray)
	assert handler.call_count == 2
	assert data2.subsets[0].subset_state.left is data.id['x']
	assert data2.subsets[0].subset_state.operator is operator.ge
	assert data2.subsets[0].subset_state.right == 3

basic test to check that subset is broadcast to a second component in the dataset.