RFR: 8293839: Documentation memory consistency effects of runLater

[Kevin Rushforth]

On Wed, 17 Aug 2022 07:21:43 GMT, Jens Lidestrom <duke at openjdk.org> wrote:

> Prior to this change it was not clear from the documentation if callers of Platform#runLater must perform
> any synchronisation to have writes of the calling thread be visible in the JavaFX Application
> Thread. It is important to document either if callers can rely on runLater to do such synchronisation
> internally, or to document is users CAN NOT rely on runLater for this.
> 
> This change documents that actions in a thread prior to submitting a runnable to
> Platform#runLater happen-before actions performed by the runnable in the JavaFX
> Application Thread.
> 
> runLater inherits the memory consistency effects of InvokeLaterDispatcher in most cases. 
> InvokeLaterDispatcher uses BlockingDeque internally. This change documents this
> in the same way as it is documented by BlockingDeque.
> 
> Other implementations of runLater should have similar memory consistency effects.

@jensli I was going through the PRs that are not marked as `rfr` (ready for review), and spotted this one. There are two needed steps before this will be marked as ready:

1. You need to file a bug report
2. You need to fix the whitespace error pointed out by `jcheck`  in the code diffs

See [CONTRIBUTING.md](https://github.com/openjdk/jfx/blob/master/CONTRIBUTING.md) for more information.

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PR: https://git.openjdk.org/jfx/pull/872