2010/10/11 Levente Uzonyi <leves@elte.hu>:
On Mon, 11 Oct 2010, Igor Stasenko wrote:
2010/10/11 Levente Uzonyi <leves@elte.hu>: On Mon, 11 Oct 2010, Igor Stasenko wrote:
On 10 October 2010 23:43, Levente Uzonyi <leves@elte.hu> wrote: On Sun, 10 Oct 2010, Igor Stasenko wrote:
A current implementation of this method
remove: oldObject ifAbsent: exceptionBlock     "Remove oldObject as one of the receiver's elements."
    oldObject ifNil: [ ^nil ].     ^(self protected: [ valueDictionary removeKey: oldObject ifAbsent: nil ])         ifNil: [ exceptionBlock value ]
simply removes a previously registered object from registry and voila.
Now lets get back to our discussion about multiple finalizers per object and using them in weak subscriptions etc.
Suppose i am added a socket to weak registry, and suppose i am added a weak subscription to it.
Now, if i do 'socket close' , it tells weak registry to remove it from list. And what we'll have: - socket handle is closed - socket is wiped from weak registry - but weak subscription still listed somewhere in a list of subscriptions
My suggestion is, that upon #remove:, a weak registry should notify all executors that object of interest are no longer takes part in finalization scheme, so they should not count on receiving #finalize eventually.
In other words:
remove: oldObject ifAbsent: exceptionBlock     "Remove oldObject as one of the receiver's elements."
    oldObject ifNil: [ ^nil ].     ^(self protected: [ | executor |       executor := valueDictionary removeKey: oldObject ifAbsent: nil.       executor discardFinalization.     ])     ifNil: [ exceptionBlock value ]
It's only an issue with the new WeakRegistry implementation, previous implementations don't have such problem. I think changing the method as you suggested, implementing WeakFinalizerItem >> #discardFinalization as "executor := nil" and changing WeakFinalizerItem >> #finalizaValues to ignore the executor if it's nil will fix the problem. Am I right?
I don't get how "multiple finalizers per object" is related to this problem at all.
No, you miss the point. When you removing object from weak registry, it is important , time to time to tell all of its executors, that they will no longer receive #finalize, because object is no longer a member of weak registry.
If you simply set executor := nil, it does nothing, an executor itself did not notified that he won't be needed in any possible future. So, if your finalization action is to remove some object(s) from the list , you'll get your list dirty after object will die, because #finalize will be never sent to your executor.
Here the simple test case:
| coll obj someWrapper | coll := OrderedCollection new. obj := Object new. someWrapper := WeakArray with: obj. coll add: someWrapper.
obj toFinalizeSend: #remove: to: coll with: someWrapper. obj finalizationRegistry remove: obj. obj := nil. Smalltalk garbageCollect. self assert: coll isEmpty
the point is, that once you doing a #remove: , your finalization scheme is broken.
I don't get you. When you remove an object from a WeakRegistry, you tell the system that you want the object removed and all related executors deleted. So the executors should never receive #finalize, they should be thrown away. Even if there's action to be done with the executors (which is pointless IMHO since those will be thrown away, but who knows), doing them is the responsibility of the sender of #remove:.
Let us get back to multiple finalizers per object, when you have two separate places, which adding possibly different executors for a single object without knowing about each other (otherwise why would you want to add two finalizers instead of one). Now if one decides to do #remove: , how to ensure that second one won't be left with dirty/invalid state?
It's not ensured, and it doesn't have to be. The sender of #remove: takes all responsibility. It can decide to add some executors back to the registry if that's necessary. If you want to keep your executors safe from some other code, which may #remove: your objects from a WeakRegistry, then you can create a private WeakRegistry and store your executors there, just like Sockets and FileStreams do.
Conclusion: weak registry don't have to support multiple finalizers per single object. Instead, if one sees the need to control a finalization of certain object(s) in own way, indepentently fron any other, then he should use a private weak registry (like Sockets and FileStreams do), and register object and its executor there. -- Best regards, Igor Stasenko AKA sig.