[Newbies] terminate event?

[Bert Freudenberg]

Am Jan 21, 2007 um 15:21  schrieb Bert Freudenberg:

> Am Jan 21, 2007 um 14:07  schrieb David Urquhart:
>
>> Hi
>>
>> I'm a Squeak beginner.  I want to write to the transcript when an  
>> object is coming to life and when its terminating.  I have an  
>> initialize method for the birth - what is the method called that  
>> fires at death?
>
> There is no such method. A message can be send to an object only if  
> there is a reference to it. As long as a reference to an object  
> exists, it is not dead, it does only get garbage-collected when the  
> last reference is removed.
>
> About the only thing you can do is to register a *different* object  
> to be notified when one object is garbage-collected. This is called  
> "finalization".

Here's an example. Evaluate this in a workspace:

	x := Object new.
	x toFinalizeSend: #show: to: Transcript with: 'He''s dead, Jim!\'  
withCRs

Nothing should happen. Then do

	x := nil

which should print "was finalized" immediately. This is because x  
still holds onto a relatively "new" object, which gets freed very fast.

However, once an object gets "old" it takes until the next full  
garbage collection (GC)! Create your object again, but this time, do  
this:

	Smalltalk garbageCollect.
	x := nil.

Nothing will be printed, because the GC reclaims all space, but also  
marks all surviving objects as "old". So even though after assigning  
nil to x your object is dead, the finalizer does not know it, yet.  
Only if you trigger a full GC again, the object's space is reclaimed,  
and the finalizer is activated.

- Bert -