Bert Freudenberg wrote:
> Michael van der Gulik schrieb:
>> I thought of a better option today: Create a "PollingService" 
>> singleton.  The process I needed was just meant to slowly poll something.
>>
>> Rather than doing "[[self doSomething] repeat ] fork", I could ask the 
>> PollingService to poll me on a regular basis. The polling service 
>> would have something like:
>>
>> PollingService>>pollObject: n
>>     | o |
>>     o := myWeakArray at: n.
>>     [ o isNil ] whileFalse: [ o poll. o:= myWeakArray at: n. ].
>>
>> So that when the object is garbage collected, the thread would also 
>> stop iterating. A very useful pattern!
>>
>> This could maybe even be done on the class side of that object.
>>
>> I hope the small amount of time between loop iterations is enough to 
>> get the GC to make the weak reference nil.
> 
> 
> Unlikely. Once an object gets tenured, only a full GC will collect it:
> 
>     http://minnow.cc.gatech.edu/squeak/1469

Ahh... I'd like to confirm that my approach indeed doesn't work, even if 
I stick a 'Smalltalk garbageCollect' in the middle of it. Argh.

Code attached, if you can be bothered looking at it.

> Do you really have random objects that are not owned by some specific 
> object that could release them?

Well, probably. I've just had another idea that I'll try.

Michael.
-------------- next part --------------
'From Squeak3.8 of ''5 May 2005'' [latest update: #6665] on 22 August 2006 at 10:07:34 pm'!
Object subclass: #TestPoller
	instanceVariableNames: 'delay'
	classVariableNames: ''
	poolDictionaries: ''
	category: 'Playing'!
!TestPoller commentStamp: 'mvdg 8/22/2006 22:07' prior: 0!
Test a polling pattern I made. It doesn't work.

p := TestPoller new.
p := nil.

Now, the transcript should stop showing 'bleep'. If your image is important, you'll need to stop the Bleeper process.!


!TestPoller methodsFor: 'as yet unclassified' stamp: 'mvdg 8/22/2006 21:43'!
initialize
	delay := Delay forSeconds: 1.
	self class startPolling: self.! !

!TestPoller methodsFor: 'as yet unclassified' stamp: 'mvdg 8/22/2006 21:42'!
poll
	Transcript show: 'bleep '.
	delay wait.! !

"-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- "!

TestPoller class
	instanceVariableNames: ''!

!TestPoller class methodsFor: 'as yet unclassified' stamp: 'mvdg 8/22/2006 22:04'!
startPolling: object
	| w x |
	w := WeakArray with: object.
	x := w at: 1.
	[ [x isNil] whileFalse: [
		x poll.
		" Try very hard to get x garbage collected:"
		x := nil.
		Smalltalk garbageCollect. 
		Processor yield.
		x := w at: 1.
	] ] forkNamed: 'Bleeper'.! !