RFR (M) 8201556: Disallow reading oops in ClassLoaderData if unloading

[Kim Barrett]

> On Apr 17, 2018, at 12:02 PM, coleen.phillimore at oracle.com wrote:
> 
> Summary: Move class_loader oop to an OopHandle, and assert that holder is alive when getting class_loader.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8201556.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8201556
> 
> Tested with mach5 tiers 1-7.
> 
> Thanks,
> Coleen

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src/hotspot/share/classfile/classLoaderData.hpp
  86   static ClassLoaderData* add_to_graph(Handle class_laoder, bool anonymous);

s/laoder/loader/

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src/hotspot/share/classfile/classLoaderData.hpp
 411   Klass* class_loader_klass() const { return _class_loader_klass; }
 412   Symbol* class_loader_name() const { return _class_loader_name; }

Maybe assert that the member being read has been set, since the
initialization happens sometime after construction.  Or will that
maybe not work because of the annoying null-class-loader?

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src/hotspot/share/classfile/classLoaderData.cpp
 942               p2i(this), p2i((void *)_class_loader.ptr_raw()), loader_name());

Why is there a (void*) cast on the class loader ptr?

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src/hotspot/share/oops/klass.hpp
 640   bool is_loader_alive(BoolObjectClosure* is_alive) const { return !class_loader_data()->is_unloading(); }

Is this just so you can defer updating is_loader_alive callers to
another RFE?

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