Thread-safe interaction between Animation and AbstractPrimaryTimer

[mstr2]

This PR ensures that internal interactions between Animation and AbstractPrimaryTimer only occur on the FX application thread.

All changes to observable state will remain instantly visible for the calling thread. However, internally, interactions with AbstractPrimaryTimer are posted to the FX thread if necessary. This is not an unsurprising change, since the callback from the FX thread was always occuring at an unspecified time in the future.

To make this work, AbstractPrimaryTimer::pause/resume/nanos will have to be synchronized to ensure field visibility across threads. In the Animation class, interactions with AbstractPrimaryTimer will be encapsulated in the new nested class AnimationPulseReceiver, which also deduplicates redundant interactions with AbstractPrimaryTimer.

For example, repeatedly calling start() and stop() in quick succession may require just a single interaction with AbstractPrimaryTimer in the future (if we ended up in the running state), or no interaction at all (if we ended up in the stopped state).

From the point of view of the caller, the API works just as it worked before: all state changes of the Animation class are instantly visible, there is no surprising change.

With this proposal, play() can be called on a background thread, and the behavior of the Animation class remains the same. If you're reading getStatus() after calling play(), you will always see that the animation is currently running (even if internally, the animation hasn't yet been added to the primary timer).

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Progress

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$ git checkout pull/1349

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jfx.git pull/1349/head

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[bridgekeeper[bot]]

:wave: Welcome back mstrauss! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk[bot]]

❗ This change is not yet ready to be integrated. See the Progress checklist in the description for automated requirements.

[bridgekeeper[bot]]

@mstr2 This pull request has been inactive for more than 8 weeks and will be automatically closed if another 8 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

[openjdk[bot]]

@mstr2 this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout fixes/animation-threadsafe
git fetch https://git.openjdk.org/jfx.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[bridgekeeper[bot]]

@mstr2 This pull request has been inactive for more than 8 weeks and will be automatically closed if another 8 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!