RFR: 8236926: Concurrently uncommit memory in G1 [v7]

[Stefan Johansson]

On Thu, 19 Nov 2020 12:56:31 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> You are correct that doing the extra notification won't hurt, but I don't really see why we should do the notification when we know it is not needed. There are probably a few improvements that we want to do when it comes to how the service thread is registering and scheduling tasks. Since this mechanism is very new I think we will realize how we want this to work more and more.
>> 
>> This is the way I see it right now (after the introduction of the public `G1ServiceThread::schedule_task()`:
>> * `G1ServiceTask::schedule(delay)` should only be called from a running task. Using it to schedule it from the outside was a bit of a hack. `schedule()` will call `G1ServiceThread::schedule(task, delay)` and nothing more.
>> * `G1ServiceThread::schedule_task(task, delay)` should be used to schedule a task from the outside. It will under the hood call `G1ServiceThread::schedule(task, delay)` and `G1ServiceThread::notify()` to handle the case where the task end up being the first task in the queue.
>> 
>> To me separating the use cases is good, but you might not agree.  We could add an assert to `G1ServiceTask::schedule(delay)` to ensure that it is only called when running on the service thread, that way we would catch wrong usage of the API quickly.
>
> I would be fine with the assert to prevent misuse.

Just pushed the assert and also update the comments a bit.

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PR: https://git.openjdk.java.net/jdk/pull/1141