RFR: 8238197: JFR: Rework setting and getting EventHandler

[Markus Grönlund]

On Thu, 10 Jun 2021 08:47:21 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

>> Greetings,
>> 
>> please help review this changeset which moves the setting and getting of event handlers to native to avoid allocations.
>> 
>> Testing: jdk_jfr, stress
>> 
>> Thanks
>> Markus
>
> src/hotspot/share/jfr/jni/jfrJavaSupport.cpp line 777:
> 
>> 775:                                                          descriptor);
>> 776:   return typed_field_holder != NULL ? typed_field_holder : ik->find_field(vmSymbols::eventHandler_name(),
>> 777:                                                                           vmSymbols::object_signature(), // untyped
> 
> When would be the event handler field untyped?

For events in java.base.

> src/hotspot/share/jfr/jni/jfrJavaSupport.cpp line 811:
> 
>> 809:   assert(java_lang_Class::as_Klass(h_mirror()) == field_holder, "invariant");
>> 810:   const oop handler_oop = JNIHandles::resolve(handler);
>> 811:   assert(handler_oop != NULL, "invariant");
> 
> Should this be rather 
> 
> if (handler_oop == NULL) {
>   return false;
> }
> 
> to have it consistent with the code in `get_handler_field_descriptor()`?

Must not be NULL when set.

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PR: https://git.openjdk.java.net/jdk/pull/4445