RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v6]

[Patricio Chilano Mateo]

On Mon, 21 Oct 2024 12:32:00 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - Rename timedWaitNonce to timedWaitSeqNo
>>  - Fix comment in Thread.java
>>  - Clear oops when thawing lockstack + add thaw_lockstack()
>
> src/hotspot/share/oops/stackChunkOop.cpp line 471:
> 
>> 469:     }
>> 470:   }
>> 471: }
> 
> Can we turn these three very similar loops into one? In my opinion, it is easier to parse.
> 
> ```C++
> void stackChunkOopDesc::copy_lockstack(oop* dst) {
>   const int cnt = lockstack_size();
>   const bool requires_gc_barriers = is_gc_mode() || requires_barriers();
>   const bool requires_uncompress = requires_gc_barriers && has_bitmap() && UseCompressedOops;
>   const auto get_obj = [&](intptr_t* at) -> oop {
>     if (requires_gc_barriers) {
>       if (requires_uncompress) {
>         return HeapAccess<>::oop_load(reinterpret_cast<narrowOop*>(at));
>       }
>       return HeapAccess<>::oop_load(reinterpret_cast<oop*>(at));
>     }
>     return *reinterpret_cast<oop*>(at);
>   };
> 
>   intptr_t* lockstack_start = start_address();
>   for (int i = 0; i < cnt; i++) {
>     oop mon_owner = get_obj(&lockstack_start[i]);
>     assert(oopDesc::is_oop(mon_owner), "not an oop");
>     dst[i] = mon_owner;
>   }
> }

Done. I combined it with the oop clearing suggestion.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1813222417