RFR: 8272107: Removal of Unsafe::defineAnonymousClass left a dangling C++ class

[David Holmes]

On 11/08/2021 3:22 am, Ioi Lam wrote:
> On Tue, 10 Aug 2021 16:37:44 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:
> 
>>> Please review this change to remove the now unused CPSlot class.  Uses of CPSlot have been replaced with Symbol*.  The change was tested by running JCK lang and VM tests, Mach5 tiers 1-2 on Linux, Mac OS, and WIndows and Macn5 tiers 3-5 on Linux x64.
>>>
>>> Thanks, Harold
>>
>> src/hotspot/share/oops/constantPool.inline.hpp line 39:
>>
>>> 37:   intptr_t adr = Atomic::load_acquire(obj_at_addr(which));
>>> 38:   assert(adr != 0 || which == 0, "cp entry for klass should not be zero");
>>> 39:   return (Symbol*)adr;
>>
>> I think you can get rid of all slot_at* and replace them with symbol_at().  Since the symbols don't change after the constant pool is initialized, all this volatile isn't needed.  Used to be used to replace Symbol* with Klass* also.  @iklam can confirm.
> 
> `ConstantPool` objects are no modified after the class is linked, and linking is done single threaded. So there's no need to use the `Atomic::load_acquire` in the above code. I agree with Coleen that the above function can be replaced with symbol_at().

The load_acquire should be matching a release_store, so does that mean 
those can be removed too? I'm not clear whether all linking must pass 
through a lock, or there are some lock-free fastpaths that might still 
need acquire/release semantics?

Cheers,
David

> -------------
> 
> PR: https://git.openjdk.java.net/jdk/pull/5070
>