[jdk19] RFR: 8289091: move oop safety check from SharedRuntime::get_java_tid() to JavaThread::threadObj() [v3]

[David Holmes]

On Tue, 28 Jun 2022 16:55:29 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> A trivial move of the oop safety check from SharedRuntime::get_java_tid() to
>> JavaThread::threadObj(). Also made adjustments to the threadObj() calls in
>> JavaThread::print_on_error() and JavaThread::get_thread_name_string() so
>> that we don't get secondary crashes when a JavaThread crashes after it has
>> detached the GC barrier.
>> 
>> Tested with Mach5 Tier[1-7]. A Mach5 Tier8 will be started this weekend.
>
> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
> 
>   dholmes CR - use Thread::current() instead of Thread::current_or_null().

src/hotspot/share/runtime/thread.cpp line 2153:

> 2151:   if (!current->is_Java_thread() || JavaThread::cast(current)->is_oop_safe()) {
> 2152:     // Only access threadObj() if current thread is not a JavaThread
> 2153:     // or if it is a JavaThread that can safely access oops.

How can a non-JavaThread safely access the oop? Is the only safe case the VMThread at a safepoint?

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PR: https://git.openjdk.org/jdk19/pull/69