RFR: 8257831: Suspend with handshakes [v2]

[Daniel D.Daugherty]

On Wed, 7 Apr 2021 07:25:29 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> src/hotspot/share/runtime/handshake.cpp line 463:
>> 
>>> 461:   ThreadInVMForHandshake tivm(_handshakee);
>>> 462:   {
>>> 463:     ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
>> 
>> Why is this needed when it is inside ThreadInVMForHandshake constructor ??
>
> If we process the async suspension handshake we can go to safepoint.
> And before safepoint we must drop the tty lock.

Is this worth a comment above the `break_tty_lock_for_safepoint()` call?

>> src/hotspot/share/runtime/thread.cpp line 1442:
>> 
>>> 1440: 
>>> 1441:     // The careful dance between thread suspension and exit is handled here:
>>> 1442:     _handshake.thread_exit();
>> 
>> I don't like the fact this hides the set_terminating call.
>> 
>> In fact I think I'd rather keep this in-line rather than tucking it away inside the handshake code. This looks too much like we're informing the handshake that the thread  is exiting rather then coordinating thread termination with a late suspension request.
>
> The problem is that we need access to the private _lock to coordinate this.

Perhaps rename the function to something like handle_thread_exit_race()?

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PR: https://git.openjdk.java.net/jdk/pull/3191