WIP: Add RefScanPolicy to object-scanning methods of Scanning#1437
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WIP: Add RefScanPolicy to object-scanning methods of Scanning#1437wks wants to merge 11 commits intommtk:masterfrom
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The VM binding only needs to know the `RefScanPolicy` trait but not its implementations.
"StrongClosure" and "StrongOnly" are too similar.
This makes the type parameter implicit and make it unnecessary to write `<_, Closure>`.
Otherwise `Closure` may be ambiguous. This also makes it looks like the `EnumName::Variant` style.
We change the `tls` from `VMWorkerThread` to `VMThread` because mutator threads can also scan objects in write barriers.
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mmtk-core introduced `RefScanPolicy` in object-scanning functions. We selectively visit strong and/or weak references according to the `RefScanPolicy`. Related PR: mmtk/mmtk-core#1437
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We add a
RefScanPolicytype parameter in object-scanning functions (scan_objectandscan_object_and_trace_edges) in theScanningtrait. It tells the VM binding whether it should visit strong and/or weak reference fields using the callback argument, and whether it should "discover" weak references in VM-specific ways if the VM chooses to do so.This PR is intended to pave a path for porting the OpenJDK-style reference processing from the
lxrbranch and eventually supporting LXR.We also made some minor changes to the object-scanning functions.
tlsparameter ofsupport_slot_enqueuing,scan_objectandscan_object_and_trace_edgesis nowVMThreadinstead ofVMWorkerThread. This allows mutator threads to scan objects in write barriers without a workaround.SlotVisitorandObjectTracertype parameters are replaced with implicitimpltypes. Because object-scanning functions now take an explicitRefScanPolicytype parameter, we makeSlotVisitorandObjectTracerimplicit to avoid the unnecessary_like inscan_object::<_, ref_scan_policy::Closure>.TODO:
lxrbranch.Decide whether we should add aWe just useRefScanPolicyimplementation for barriers.ref_scan_poilcy::StrongOnlyfor the SATB barrier.Fixes: #1376
Fixes: #1375