RFR: 8266846: Add java.time.InstantSource

[Stephen Colebourne]

On Sat, 15 May 2021 21:32:54 GMT, Ralph Goers <github.com+120415+rgoers at openjdk.org> wrote:

>> 8266846: Add java.time.InstantSource
>
> Can you possibly find a way that this can be used in a garbage free manner?  Providing a MutableInstant interface that allows the Instant object to be provided and have its values set by a currentInstant(MutableInstant instant) method would solve the problem nicely for Log4j - or any other app that is trying to avoid allocating new objects. I believe this also aligns with what [Michael Hixson](https://github.com/michaelhixson) is asking for.
> 
> An alternative would be for java.time to maintain a pool of Instants that apps like Log4j can somehow control, but that would seem far more complicated.

@rgoers Michael's request has been handled, which was a simple change to the wording. What you need cannot be accomplished because `Instant` has a restricted design due to the Valhalla project.

A `MutableInstant` class can have its own `now()` method that does whatever is necessary to initialize it, so there is no need to refer to it here.

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PR: https://git.openjdk.java.net/jdk/pull/4016