Update to MMTk core PR #609 (#162)

Author: qinsoon

mmtk/Cargo.toml

@@ -28,7 +28,7 @@ once_cell = "1.10.0"
 # - change branch
 # - change repo name
 # But other changes including adding/removing whitespaces in commented lines may break the CI.
-mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "662c9015e59044f0114c8a69663055fac1212544" }
+mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "f78de4ed8ffd6f834c6c3d3a0bde0a651cc33f2b" }
 # Uncomment the following to build locally
 # mmtk = { path = "../repos/mmtk-core" }
 

mmtk/src/reference_glue.rs

@@ -8,6 +8,8 @@ use mmtk::vm::ReferenceGlue;
 pub struct VMReferenceGlue {}
 
 impl ReferenceGlue<OpenJDK> for VMReferenceGlue {
+    type FinalizableType = ObjectReference;
+
     fn set_referent(reff: ObjectReference, referent: ObjectReference) {
         let oop = Oop::from(reff);
         unsafe { InstanceRefKlass::referent_address(oop).store(referent) };