RFR: 8259851: Using boolean type for tasks in SubTasksDone

[Kim Barrett]

On Mon, 18 Jan 2021 14:17:21 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Changing `uint` to `bool` in `SubTasksDone`, since atomic operations on `bool` are well supported.
> 
> Tested: hotspot_gc

Should this change be made? I understand the intent is to use the
semantically intended type, and agree with that intent. But there is a
hidden cost; some platforms don't directly support cmpxchg on byte sized
values, and use CmpxchgByteUsingInt. Maybe that cost is in the noise, but
the question should be considered.  For Zero I don't care.  But there are
affected platforms.

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PR: https://git.openjdk.java.net/jdk/pull/2131