Dear Squeakers,

I have met the problem of generating objects which are not GC'ed as they
should, while debugging drag&drop functionality for the morphic
Browsers.
It arises, if there is something interrupting a correct drag&drop
operation (e.g. a Debugger) and Morphs to visualize the drag&drop
operation remain. Removing these Morphs isn't a problem, but sometimes
some Browser (models) seem to be referenced by some root object. I have
searched for them quiet a long time (by SystemDictionary>>pointersTo:),
but with no success.

I don't know where the problem is, but I have some observations:
- EventHandlers in PluggableListMorphs reference browser models;
- Browsers reference SystemWindows, PluggableListMorphs, etc.;
- abandon/delete semantic for Morphs is not clear to me.

Some questions:

Is there an easy to use method to find root objects of a set of objects?

Isn't it true, that Squeak has no problems collecting garbage of objects
with cyclic references?

What could these root guys are, which hold morphs not #deleted
correctly?

What could these root guys are, which hold morphs #deleted correctly?

Isn't it true, that it is OK to just delete the parent Morph of some
submorphs and let GC do the rest?


Any ideas, hints, answers are very appreciated...


BTW:

Code that seems to work for me - though I don't know exactly what in it
(it has arised by many manually trials, and I just wanted to get rid of
these annoying objects!), but it seems to be setting model to nil for
Morphs referencing the Browser - is:
----

Utilities>>dragNDropDomestosStrong
	"for breaking bad dependencies"
	| winsWithoutOwner browserWins modelsWithDependents obsoleteModels
morphs |
	self dragNDropDomestos.
	browserWins _ SystemWindow allInstances select: [:sw | sw model
isKindOf: Browser].
	winsWithoutOwner _ browserWins select: [:bw | bw owner isNil].
	winsWithoutOwner do: [:win | win allMorphs do: 
			[:sm | 
			(sm respondsTo: #model)
				ifTrue: [sm model: nil].
			sm abandon]].
"<comment>"
	"modelsWithoutDependents _ Browser allSubInstances select: [:bi |
bi        
	    dependents isEmpty].            
	modelsWithoutDependents do: [:model | (Smalltalk pointersTo:
model)        
	    do:             
	[:ref |             
	ref isMorph ifTrue: [ref abandon].            
	((ref respondsTo: #model)            
	and: [ref model == model])            
	ifTrue: [ref model: nil]]].           
	"
"</comment>"
	modelsWithDependents _ Browser allSubInstances select: [:bi | bi
dependents isEmpty not].
	obsoleteModels _ modelsWithDependents
				select: [:model | (model dependents
						detect: [:dep | (dep isKindOf: SystemWindow)
								and: [dep owner isNil]]
						ifNone: []) notNil or: [(model dependents detect: [:dep2 | dep2
isKindOf: SystemWindow]
							ifNone: []) isNil]].
	obsoleteModels do: 
		[:model | 
		morphs _ model dependents
					select: [:dep | dep isMorph and: [dep pasteUpMorph isNil]].
		morphs do: 
			[:m | 
			m abandon.
			((m respondsTo: #model)
				and: [m model == model])
				ifTrue: [m model: nil]]].
	Smalltalk garbageCollect

----

Greetings,

Stephan
-- 
Stephan Rudlof (sr at evolgo.de)
   "Genius doesn't work on an assembly line basis.
    You can't simply say, 'Today I will be brilliant.'"
    -- Kirk, "The Ultimate Computer", stardate 4731.3