Hi Mariano, Hi All,
response below. But does anyone have any tests for the image segment
primitives? I'm refactoring them and would like some tests.
2010/6/3 Mariano Martinez Peck <[email protected]>
> Hi. ImageSegment uses GC to compute the out pointers. Basically, to a given
> array of roots (a graph) it does:
>
> 1) It marks the rootArray and all root objects by turning on the Garbage
> Collector bit in the object header of those particular objects.
> 2) Then does a mark pass over all objects. This will stop at our marked
> roots leaving our segment unmarked in their shadow.
> 3) Finally, it unmarks the rootArray and all root objects.
> 4) Only external objects are now marked.
>
> The unmarked objects in the graph of objects of the arrays are those who
> will be put in the WordArray (the segment) and those who are marked to the
> outPointers.
>
> However, I don't see where step 2) is done in Interpreter >>
> primitiveStoreImageSegment
>
> In a piece of such method it does:
>
>
> "Then do a mark pass over all objects. This will stop at our marked roots,
> thus leaving our segment unmarked in their shadow."
> savedYoungStart := youngStart.
> youngStart := self startOfMemory. "process all of memory"
> "clear the recycled context lists"
> freeContexts := NilContext.
> freeLargeContexts := NilContext.
> self markAndTraceInterpreterOops. "and special objects array"
> youngStart := savedYoungStart.
>
> "Finally unmark the rootArray and all root objects."
> self longAt: arrayOfRoots put: ((self longAt: arrayOfRoots) bitAnd:
> AllButMarkBit).
> ......continue.......
>
> But here I see it is only marking Interpreter oops, not all objects. And I
> don't see where all objects are marked even in the code that follows this
> little piece.
>
markInterpreterOops marks all objects accessible from the interpreter oops,
including the specialObjectsArray, recursively marking any unmarked objects
and their referents. i.e. it marks all objects reachable from the roots of
the system. This would mark all objects in the system were it not for the
fact that the primitive marks the rootArray and so markInterpreterOops does
not marl objects /only/ reachable from the rootArray. So once the rootArray
objects have been unmarked, only those objects that should go in the image
segment are unmarked.
So the primitive works by
- marking the objects in rootArray, preventing marking of objects reachable
from them in the next step
- recursively marking all objects reachable from the roots (except those
already marked)
- unmarking root objects, leaving the transitive closure of objects
accessible from the roots and no where else unmarked
- writing the unmarked objects to an image segment
HTH
Eliot
> You can see the comment: "Then do a mark pass over all objects" and even
> without the comment it makes sense to mark all objects in order to detect
> outPointers.
>
> Does anyone has a hint?
>
> Thanks
>
> Mariano
>
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