RFR: 8264788: Make SequentialSubTasksDone use-once

[Albert Mingkun Yang]

On Wed, 7 Apr 2021 08:32:11 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   can I have reviews for this change that simplifies code ahead?
> 
> SequentialSubTasksDone has some machinery to reset itself automatically after all tasks were claimed.
> 
> This is not used at all and can/should be removed. 
> 
> Test: tier1-3

Looking at how `SequentialSubTasksDone` is used, I don't really see the benefit of having `assert(_num_claimed == _num_tasks)` in the destructor. If we drop that assertion, `Atomic::add` is more readable.

I prefer `Atomic::add` with the assertion removed, but this version is fine as well.

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Marked as reviewed by ayang (Committer).

PR: https://git.openjdk.java.net/jdk/pull/3372