RFR: 8249004: Reduce ThreadsListHandle overhead in relation to direct handshakes [v10]

[Daniel D.Daugherty]

On Wed, 3 Nov 2021 01:21:50 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8249004.cr2.patch
>
> src/hotspot/share/runtime/thread.cpp line 446:
> 
>> 444:   Thread* current_thread = nullptr;
>> 445:   if (checkTLHOnly) {
>> 446:     current_thread = Thread::current();
> 
> This seems redundant due to line 463. You can just have a `if (!checkTLHOnly)` block here.

I suspect that the way that git is displaying the diffs is confusing you.

We need `current_thread` set if we get to line 474 so we have to init
`current_thread` on line 446 for the `checkTLHOnly == true` case and
on line 463 for the `checkTLHOnly == false` case.

I could simplify the logic by always setting current thread when it is
declared on 444, but I was trying to avoid the call to `Thread::current()`
until I actually needed it. I thought `Thread::current()` can be expensive.
Is this no longer the case?

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PR: https://git.openjdk.java.net/jdk/pull/4677