RFR: 8254231: Implementation of Foreign Linker API (Incubator) [v4]

[Jorn Vernee]

On Thu, 15 Oct 2020 22:42:49 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Re-add file erroneously deleted (detected as rename)
>
> src/hotspot/cpu/x86/foreign_globals_x86.cpp line 56:
> 
>> 54: }
>> 55:
>> 56: const ABIDescriptor parseABIDescriptor(JNIEnv* env, jobject jabi) {
> 
> I don't know if you care about performance but of these env->calls transition into the VM and back out again.  You
> should prefix all the code that comes from java to native with JNI_ENTRY and just use native JVM code to implement
> these.

Currently this is prefixed with `JVM_ENTRY` e.g. like:
JVM_ENTRY(jlong, PI_generateAdapter(JNIEnv* env, jclass _unused, jobject abi, jobject layout))
  {
    ThreadToNativeFromVM ttnfvm(thread);
    return ProgrammableInvoker::generate_adapter(env, abi, layout);
  }
JVM_END
(where `generate_adapter` ends up calling `parseABIDescriptor`)

JVM_ENTYRY seems to be mostly the same except for JNI_ENTRY having a `WeakPreserverExceptionMark` as well. Do we need
to switch these? Also, I guess if we want to use VM code directly, we should get rid of the `ThreadToNativeFromVM` RAII
handle.

-------------

PR: https://git.openjdk.java.net/jdk/pull/634