RFR: 8343177: JFR: Remove critical section for thread id assignment

[Markus Grönlund]

On Wed, 30 Oct 2024 05:38:35 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Sorry I struggled to map the code changes to the description of the changes. I think I'm missing some background context here - what is the "traceid" of a thread?

A traceid is a unique, monotonic ID that JFR assigns to artifacts (instances) (Threads, Klasses, Methods, Symbols).

Invariant; no reuse of IDs.

With Loom, unique monotonic ID is intrinsic to the tid field of the threadObj.

> src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 106:
> 
>> 104:   assert(Thread::is_starting_thread(jt), "invariant");
>> 105:   assert(jt->threadObj() == nullptr, "invariant");
>> 106:   jt->jfr_thread_local()->_jvm_thread_id = 1;
> 
> Is this supposed to reflect the `java.lang.Thread` thread-id? If so this is changing to 3 with the object monitor virtual thread changes.

If the primordial thread ID assignment is changed from 1 to 3, then that will have to be updated, of course.

> src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 438:
> 
>> 436: 
>> 437: #ifdef ASSERT
>> 438: static bool assignment_precondition(const Thread* t, JfrThreadLocal* tl) {
> 
> Suggestion:
> 
> static bool can_assign(const Thread* t, JfrThreadLocal* tl) {

Good suggestion.

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PR Comment: https://git.openjdk.org/jdk/pull/21756#issuecomment-2446715237
PR Review Comment: https://git.openjdk.org/jdk/pull/21756#discussion_r1822423968
PR Review Comment: https://git.openjdk.org/jdk/pull/21756#discussion_r1822424296