566043 - Can we get rid of virtual methods on ScriptObject?

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Virtual Machine, enhancement)

Description

[Steven Johnson]

We could move all of the internal-only-override behavior from the existing C++ virtual methods, into a table of C functions on our own VTable method. This would allow us to entirely get rid of the C++ vtable, saving a pointer-sized field per ScriptObject. 

Pros:
-- Memory savings.
-- Possibly cleaner glue code as a result, with less tightly-coupled-via-inheritance issues between VM and client

Cons:
-- Lots of work; much of existing glue code would need to be touched
-- Unclear if memory savings would be worthwhile
-- This would require all glue classes to be *prohibited* from having any virtual methods, to avoid a C++ vtable creeping back in and mucking up our memory layout

Throwing it out there for PACMAN consideration; there are probably other pros or cons I haven't thought of.

Comment 1

[Lars T Hansen]

Memory savings are not really interesting to PACMAN - better elucidation of benefits desired.

Comment 2

[Edwin Smith]

As long as ScriptObject is a GCFinalizedObject, won't it still need a C++ vtable for the virtual destructor?

Comment 3

[Lars T Hansen]

(In reply to comment #2)
> As long as ScriptObject is a GCFinalizedObject, won't it still need a C++
> vtable for the virtual destructor?

It will, and more virtual GC methods are probably coming.

Comment 4

[Steven Johnson]

(In reply to comment #1)
> Memory savings are not really interesting to PACMAN - better elucidation of
> benefits desired.

Agreed, this was more of a "save this idea for future consideration" bug.

(In reply to comment #2)
> As long as ScriptObject is a GCFinalizedObject, won't it still need a C++
> vtable for the virtual destructor?

Ah, yes, this is true. (Unless we find a way to hook up a finalizer via our VTable... which would be doable but probably fiddly.)

Comment 5

[Sylvestre Ledru [:Sylvestre]]

Tamarin is a dead project now. Mass WONTFIX.

Comment 6

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.