RFR: 8212107: VMThread issues and cleanup [v6]

[Robbin Ehn]

On Mon, 28 Sep 2020 18:32:17 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> If GuaranteedSafepointInterval is set to a lower value than the default on the command line, then I'm okay if
>> SafepointALot does not do anything extra. However, if GuaranteedSafepointInterval is either the default value or is set
>> to a higher value, then I would like SafepointALot to cause a safepoint more frequently than the
>> GuaranteedSafepointInterval. Every GuaranteedSafepointInterval/4 would be a fine definition of "a lot".
>
> Mulling on this more... is it too radical to consider that we no longer need SafepointALot?

I would like SafepointALot(and HandshakeALot) to be executed in a separate thread and that randomly request a safepoint
(preferably with some validation inside the operation). Since VM thread now handles this it can not do this request
while busy. Also having the VM thread 'more' sporadic waking up will be confusing for the VM thread loop.

So I agree with you that we need a better SafepointALot, but I think it wrong to use the VM thread to drive it.
I suggest we create an enhancement for it.

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PR: https://git.openjdk.java.net/jdk/pull/228