RFR: 8258032: Reconsider LEAF entry restrictions

[Coleen Phillimore]

On Thu, 7 Jan 2021 21:20:49 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Please review the smaller version of this enhancement.  JRT_LEAF can allow Handles.  Fixed places where a ResetNoHandleMark was added to workaround the restriction and remove some obsolete comments in deoptimization (the function is a JRT_BLOCK_ENTRY that has a HandleMarkCleaner which cleans up the HandleMark to the one before call_stub() in JavaCalls. A HandleMarkCleaner also allows HandleMark and Handles.
>> 
>> Tested with tier1-3, 4-6 with the larger change and 7-8 in progress.
>
> src/hotspot/share/gc/z/zVerify.cpp line 376:
> 
>> 374: // is no safepoint to protect against, and fiddling around with exceptions.
>> 375: class StackWatermarkProcessingMark {
>> 376:   HandleMark            _hm;
> 
> Since you're removing the ResetNoHandleMark, you should revisit
> the comment block for the class. The entire sentence to revisit is:
> // ... It is mostly
> // due to problems that we might want to eventually clean up inside of the
> // frame iteration code, such as creating random handles even though there
> // is no safepoint to protect against, and fiddling around with exceptions.

This statement is still true.  PreserveExceptionMark creates a Handle, so we need the HandleMark.  We don't need to ResetNoHandleMark with this change.

PreserveExceptionMark::PreserveExceptionMark(Thread*& thread) {
  thread     = Thread::current();
  _thread    = thread;
  _preserved_exception_oop = Handle(thread, _thread->pending_exception());

(which will create a Handle if there's a pending_exception).

> src/hotspot/share/runtime/interfaceSupport.inline.hpp line 493:
> 
>> 491:     ThreadInVMfromNative __tiv(thread);                              \
>> 492:     debug_only(VMNativeEntryWrapper __vew;)                          \
>> 493:     debug_only(ResetNoHandleMark __rnhm;)                            \
> 
> Your fix for JDK-8259374 adds a ResetNoHandleMark to
> ThreadInVMfromNative so new L493 isn't needed.

Oh you're right.  I'd missed this in the original.  I'll remove this after I checkin the first one.

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PR: https://git.openjdk.java.net/jdk/pull/1990