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

[Daniel D. Daugherty]

On Mon, 27 Jun 2022 00:48:43 GMT, David Holmes <dholmes 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.
>
> src/hotspot/share/runtime/thread.cpp line 2150:
> 
>> 2148: void JavaThread::print_on_error(outputStream* st, char *buf, int buflen) const {
>> 2149:   st->print("%s \"%s\"", type_name(), get_thread_name_string(buf, buflen));
>> 2150:   if (is_oop_safe()) {
> 
> This is wrong - `is_oop_safe` only has relevance when called on the current JavaThread. It is the current thread that must be oop_safe, not the target thread we are printing.

Agreed. I had that nagging feeling when I thought about this fix
while working on chores on Sunday...

> src/hotspot/share/runtime/thread.cpp line 2213:
> 
>> 2211: const char* JavaThread::get_thread_name_string(char* buf, int buflen) const {
>> 2212:   const char* name_str;
>> 2213:   if (is_oop_safe()) {
> 
> Same comment - it is the current thread that must be oop_safe. If the target thread has exited then we will detect that via the null threadObj.

Agreed.

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