RFR: 8223312: Utilize handshakes instead of is_thread_fully_suspended [v2]

[Richard Reingruber]

On Tue, 20 Oct 2020 11:55:49 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Removed TraceSuspendDebugBits
>>  - Removed unused method is_ext_suspend_completed_with_lock
>
> Still looks good.

Hi,

this is a good change, because it is a simplification and it it makes the stack walks safe by doing them as part of a
handshake.

The change conflicts with #119 though. This one is ready to be pushed since last week but was delayed due to other
interferences. Would you mind me integrating #119 first? After integration it would be needed to pull 2 EscapeBarriers
out of handshakes. Of course I would help do that.

Thanks, Richard.

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PR: https://git.openjdk.java.net/jdk/pull/729