On Fri, 16 Dec 2022 02:10:09 GMT, David Holmes <[email protected]> wrote:
>> Now the `JvmtiVTMSTransitionDisabler` mechanism supports disabling VTMS
>> transitions for all virtual threads only. It should also support disabling
>> transitions for any specific virtual thread as well. This will improve
>> scalability of the JVMTI functions operating on target virtual threads as
>> the functions can be executed concurrently without blocking each other
>> execution when target virtual threads are different.
>> New constructor `JvmtiVTMSTransitionDisabler(jthread vthread)` is added
>> which has jthread parameter of the target virtual thread.
>>
>> Testing:
>> mach5 jobs are TBD (preliminary testing was completed):
>> - all JVMTI, JDWP, JDI and JDB tests have to be run
>> - Kitchensink
>> - tier5
>
> src/hotspot/share/classfile/javaClasses.cpp line 1745:
>
>> 1743: int val = VTMS_transition_disable_count(java_thread);
>> 1744:
>> java_thread->int_field_put(_jvmti_VTMS_transition_disable_count_offset, val
>> - 1);
>> 1745: }
>
> These are not thread-safe functions. What constraints exist for using these
> methods safely?
> Update: looks like they must be called with the lock held so we should assert
> that.
> Should also assert the count never goes negative (which I assume would be an
> error?).
Each of these two functions is called just once with the lock held.
I feel that asserting this would be an overkill but I can add it if you still
think it is important.
I've added assert for negative count.
> src/hotspot/share/prims/jvmtiThreadState.cpp line 252:
>
>> 250: return; // JvmtiVTMSTransitionDisabler is no-op without virtual
>> threads
>> 251: }
>> 252: if (Thread::current_or_null() == NULL) {
>
> Nit: please use `nullptr` in new code
Done.
-------------
PR: https://git.openjdk.org/jdk/pull/11690
