RFR: 8276658: Clean up JNI local handles code

[Coleen Phillimore]

On Thu, 11 Nov 2021 06:52:45 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> JNI Local handles can only be created by JavaThread (there's an assert in make_local) but the fields are added to Thread.
>> Move the fields to JavaThread and adding JavaThread* argument.
>> Also, the global freelist isn't very useful now that global JNI handles don't use JNIHandleBlock, so the locking that claims incorrectly to block for safepoint is removed.
>> Lastly, there's at least 3 places that duplicate pushing a new JNIHandleBlock to the thread for temporarily adding JNI local handles. These have been moved to common code with a JNIHandleMark object, moved from jvmci code.
>> The commits are separate to help reviewing, but the entire change has been tested together with tier1-6.
>> The commits in this change have been performance tested individually and together with no meaningful differences from mainline.
>
> src/hotspot/share/compiler/compileBroker.cpp line 2324:
> 
>> 2322:   // Remove the JNI handle block after the ciEnv destructor has run in
>> 2323:   // the previous block.
>> 2324:   pop_jni_handle_block();
> 
> Does the fact the JNIHandleMark destructor won't get executed until much later, at the end of this method, make any difference?

I don't think so because most of the rest of the function is logging and it doesn't seem to do anything with JNIHandles afterwards, so there are no handles created that shouldn't be removed in that code range.

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PR: https://git.openjdk.java.net/jdk/pull/6336