RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v5]

[David Holmes]

On Thu, 24 Oct 2024 03:31:02 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> src/hotspot/share/runtime/objectMonitor.hpp line 302:
>> 
>>> 300:   void      set_owner_from(int64_t old_value, JavaThread* current);
>>> 301:   // Set _owner field to tid of current thread; current value must be ANONYMOUS_OWNER.
>>> 302:   void      set_owner_from_BasicLock(JavaThread* current);
>> 
>> Shouldn't tid there be the basicLock?
>
> So the value stored in _owner has to be ANONYMOUS_OWNER. We cannot store the BasicLock* in there as before since it can clash with some other thread's tid. We store it in the new field _stack_locker instead.

Right I understand we can't store the BasicLock* directly in owner, but the naming of this method has me confused as to what it actually does. With the old version we have:

Before: owner = BasicLock* belonging to current
After: owner = JavaThread* of current

with the new version we have:

Before: owner = ANONYMOUS_OWNER
After: owner = tid of current

so "BasicLock" doesn't mean anything here any more. Isn't this just `set_owner_from_anonymous` ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1814330162