514488 - Pause time of FinishIncrementalMark is not properly bounded

Status: RESOLVED WONTFIX

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

Description

[Lars T Hansen]

There are several problems here:

- the time of the final root and stack scan is bounded only by heap size
- the time of running finalizers is not bounded at all (user code runs)
- sweep time is not bounded, but this does not appear to be a problem in practice

It's hard to fix this because we must run the final root and stack scan synchronously to ensure GC termination; if we have a budget for that and can exhaust it we will have to start over again during the next cycle.  This can be fixed but requires fancy handling of the stack - don't rescan portions that haven't changed, for example - and probably write barriers on roots, which is going to be a hard sell for now.

Another problem is that with reference counting and having users' destructors responsible for the final decrementing of references during destruction, we must run destructors synchronously during GC or risk not reclaiming memory.  The correct fix here is to abandon RC or at least decouple user destructors from GC destructors - in practice few objects will have user destructors, and those that don't can be destroyed synchronously, while destruction of the rest can be delayed.

Comment 1

[Lars T Hansen]

Fixes for finalization are a hot item for upcoming work.

Comment 2

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.