RFR: 8240466: AppJSCallback* apps launched by ModuleLauncherTest intermittently hang

[Kevin Rushforth]

While testing JavaFX using gradle 6.3-nightly and JDK 14, I ran into what turned out to be a latent test bug in the AppJSCallback* apps that are launched by ModuleLauncherTest. The launched apps construct a WebView instance, obtain a WebEngine instance from the WebView, add a state listener to the WebEngine, load the web content, and then return from the Application::start method. The WebView instance is held a local variable, and so is subject to garbage collection once it goes out of scope when the start method returns.

In addition, the test apps did not check for successful launching of the application or successful loading of the web content, which led to the test suite hanging (else it would have been a simple test failure).

Note that I don't know (nor care) what changed in JDK 14 to make this more likely to occur, but since the test itself is demonstrably wrong, it needs to be fixed.

The main part of the fix was to make the WebEngine an instance variable. In order to make the test more robust, I also modified it to launch the application in another thread, and having the main thread check that the application launched successfully and that the web content was loaded successfully, after which I did the assertion check for the correct number of callbacks.

The 5 different apps only differ from each other in the name of the class, the name of the package from which MyCallback is imported, and possibly the expected number of callbacks. I diffed AppJSCallbackExported.java against the other 4 test files and the diffs are essentially the same as they were before this change. Reviewers thus only need to review one of the tests in detail.

For example, here are the diffs between AppJSCallbackExported and AppJSCallbackUnexported:

$ diff .../AppJSCallbackExported.java .../AppJSCallbackUnexported.java

37c37
< import myapp5.pkg2.MyCallback;
---
> import myapp5.pkg1.MyCallback;
45c45
< public class AppJSCallbackExported extends Application {
---
> public class AppJSCallbackUnexported extends Application {
77c77
<             Util.assertEquals(1, callbackCount);
---
>             Util.assertEquals(0, callbackCount);

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Commits:
 - c70d3995: 8240466: AppJSCallback* apps launched by ModuleLauncherTest intermittently hang

Changes: https://git.openjdk.java.net/jfx/pull/134/files
 Webrev: https://webrevs.openjdk.java.net/jfx/134/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8240466
  Stats: 265 lines in 5 files changed: 205 ins; 5 del; 55 mod
  Patch: https://git.openjdk.java.net/jfx/pull/134.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/134/head:pull/134

PR: https://git.openjdk.java.net/jfx/pull/134