RFR: 8296324: JVMTI GetStackTrace truncates vthread stack trace for agents loaded into running VM [v2]

[Chris Plummer]

On Thu, 17 Nov 2022 17:35:32 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> The `VirtualThread` static field `notifyJvmtiEvents` is not set correctly in cases JVMTI agents are loaded into running VM. It is because an extra call to java_lang_VirtualThread::init_static_notify_jvmti_events() is needed.
>> This function is called once at the VM initialization, so this extra call is not necessary for agent loaded at startup.
>> 
>> Testing:
>> New test is added: `test/hotspot/jtreg/serviceability/jvmti/vthread/VirtualStackTraceTest`
>> This test is failed without fix and passed with it.
>> TBD: run all JVMTI and JDI test in mach5.
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add @requires vm.jvmti to VirtualStackTraceTest

Changes requested by cjplummer (Reviewer).

src/hotspot/share/prims/jvmtiExport.cpp line 385:

> 383:   if (Continuations::enabled()) {
> 384:     // Virtual threads support. There is a performance impact when VTMS transitions are enabled.
> 385:     if (!java_lang_VirtualThread ::notify_jvmti_events()) {

remove extra space before ::

src/hotspot/share/prims/jvmtiExport.cpp line 390:

> 388:         ThreadInVMfromNative tiv(JavaThread::current());
> 389:         java_lang_VirtualThread::init_static_notify_jvmti_events();
> 390:       }

Doesn't this logic mean that if the first pass through this code is made with an unattached thread, then that will prevent subsequent passes from calling `init_static_notify_jvmti_events`, even if the thread is attached. The reason is because `java_lang_VirtualThread::set_notify_jvmti_events(true);` will already have been done, so you won't pass the `if (!java_lang_VirtualThread ::notify_jvmti_events())` check.

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PR: https://git.openjdk.org/jdk/pull/11204