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

[Daniel D. Daugherty]

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().

This latest version has only been tested with Mach5 Tier1 so far.

In JavaThread::get_thread_name_string() and when you look at the PR with
white space changes disabled, you'll see this new code which is executed
in the "normal code" case:


  Thread* current = Thread::current_or_null_safe();
  assert(current != nullptr, "cannot be called by a detached thread");
  if (!current->is_Java_thread() || JavaThread::cast(current)->is_oop_safe()) {
    // Only access threadObj() if current thread is not a JavaThread
    // or if it is a JavaThread that can safely access oops.

so I've switched to `Thread::current_or_null_safe` and added an
assert() for the `current` value not being `nullptr`.

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

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