RFR: 8264004: Don't use TRAPS if no exceptions are thrown [v2]

[Coleen Phillimore]

On Tue, 23 Mar 2021 05:52:51 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> src/hotspot/share/prims/jvmtiRedefineClasses.hpp line 484:
>> 
>>> 482:   void rewrite_cp_refs_in_method(methodHandle method,
>>> 483:     methodHandle * new_method_p, TRAPS);
>>> 484:   bool rewrite_cp_refs_in_methods(InstanceKlass* scratch_class, TRAPS);
>> 
>> This method clears any pending exception and so should not be a TRAPS method.
>
> `VM_RedefineClasses::load_new_class_versions` also seems to never throw. These functions should be changed to take a `Thread*` parameter, and should use `HandleMark em(thread);` to guarantee that an exception never leaves the function.

Both of these functions are good examples of the convention that we're trying to agree on.   In, load_new_class_versions, TRAPS is passed to materialize THREAD.  THREAD is used then in a lot of places, and also to pass to SystemDictionary::parse_stream(...TRAPS), which does have an exceptional return that must be handled.
Removing TRAPS then adding:
JavaThread* current = JavaThread::current();
changing THREAD to current in most of the places seems ok, but passing 'current' to SystemDictionary::resolve_from_stream loses the information visually that this function returns an exception that must be handled.
We need some meta-writeup rather than these decisions made in pull requests, because if we made these decisions collectively, I missed out.

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PR: https://git.openjdk.java.net/jdk/pull/3141