RFR: 8263322: Deadlock when calling Application.launch in the FXThread after Platform.startup [v2]

[Kevin Rushforth]

On Wed, 10 Mar 2021 17:24:47 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> `Initalize the FX runtime via Platform.startup and then launch an Application on another thread (should succeed)`
>> I don't think that should succeed. I would expect it to throw an exception. If that would be the case, then both startup-methods would result in different states, which wouldn't be so good.
>> 
>> I've now restructured the tests.
>> It's a total of 4 tests. 2 after Application.launch and 2 after Platform.startup. 
>> In both cases I check what happens, a Application is launched from another thread, or from the javafx thread. In all cases an exception is expected.
>
>> Initalize the FX runtime via Platform.startup and then launch an Application on another thread (should succeed)
> I don't think that should succeed. I would expect it to throw an exception. If that would be the case, then both startup-methods would result in different states, which wouldn't be so good.
> 
> No, this really should succeed. Internally, it is a similar case to what the special Java launcher method does when launching a Java class that extends `Application` and which may have a main method that calls `Application.launch`. We check the various cases of launching an application with/without it extending `Application` in the tests under [tests/system/src/test/java/test/launchertest/](https://github.com/openjdk/jfx/tree/master/tests/system/src/test/java/test/launchertest/).

To further clarify, `Application.launch` will start the FX platform only if it is not already started by some other means. Then it will (in all cases) run the applicaiton life-cycle.

Note this from the `Application` class docs:

Life-cycle

The entry point for JavaFX applications is the Application class. The JavaFX runtime does the following, in order, whenever an application is launched:

1. Starts the JavaFX runtime, if not already started (see Platform.startup(Runnable) for more information)
...

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PR: https://git.openjdk.java.net/jfx/pull/421