604333 - Clean up finalization

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Garbage Collection (mmGC), defect, P3)

Description

[Lars T Hansen]

There are several problems here.

Right now the finalization pass in the GC scans the entire heap and calls the destructor on anything that has a destructor.  Since we use reference counted objects extensively, many destructors are called.  The scan and the destructor calling can take a long time and are the main cause of visible/audible pauses in the Flash Player.

When reference counting is removed there will be many fewer objects that has interesting destructors, and we need a scheme (header bits, segregated allocation, change in base classes?) that allows us to scan only the ones that do have finalizers.  Doing that should get rid of the finalization problem in most cases.

The other problem is reference counting semantics: right now an object is finalized as it is destructed, but that means that if two objects are eligible for GC at the same time they will be finalized and destructed in some order.  No fixed order is correct if one references the other and needs to access the other during its own finalization.  Ergo finalization - which should be a limited activity for a few types - needs to be decoupled from destruction.  There are many existing approaches to that (ephemerons, guardians, will executors, reference queues) and we may need solutions for both AS3 and C++.

If we find a good finalization mechanism for C++ we may no longer need the presweep callback, and that will probably simplify the GC a bit and remove some corner cases.

Comment 1

[Sylvestre Ledru [:Sylvestre]]

Tamarin is a dead project now. Mass WONTFIX.

Comment 2

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.