[Webkit-unassigned] [Bug 148914] GCAwareJITStubRoutines should be GC cells

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=148914

--- Comment #1 from Filip Pizlo <fpizlo at apple.com> ---
This could also be addressed by having stub routines hold RefPtr's to each other.  For example, in the case of a getter, we have the following objects:

1) PolymorphicAccess
2) AccessCase
3) CallLinkInfo
4) JITStubRoutine for PolymorphicAccess
5) JITStubRoutine for CallLinkInfo

Currently we would have the following ownership/ref rules:

(1) owns (2)
(2) owns (3)
(1) refs (4)
(3) refs (5)

Everything would be fine if we also added:

(5) refs (4)

This feels like it might be a bit ad-hoc and certainly not as flexible if these were GC cells.  But, it would work!

In particular:
- If (5) gets deleted, then (3)->(5) must have been cleared first.
- If (4) gets deleted, then (1)->(4) and (5)->(4) must have been cleared first.
- If the owning stub gets destroyed, then everyone gets deleted.

Basically, there is no case where things leak and there is no case where a dangling pointer is left behind.

This could be implemented by giving CallLinkInfo a pointer to its owning JIT stub routine, or more generally, its "JIT owner".  This would mean that we'd also have:

(3) refs (4).

Then, when the CallLinkInfo needs to spawn a stub routine, it can ensure that this new stub routine refs the stub that owned the CallLinkInfo.

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