RFR: 8264990: WebEngine crashes with segfault when not loaded through system classloader [v3]

[Matthias Bläsing]

> The functions from FileSystemJava are called from different threads the
> root problem manifests because the JNI FindClass function behaves
> differently when called from a context that is the ancestor of a java
> frame compared to when called in isolation.
> 
> A segmentation fault is observed when local storage of a webview is
> accessed. At that time a new native thread is spun up and that sets up
> the local storage, by calling into the JVM via
> WTF::FileSystem::makeAllDirectories. At that point GetFileSystemClass is
> invoked to get a referenc to the java implementation of the FileSystem.
> As this is is called from a new native thread (no java context
> available), JNI uses the system classloader to locate the class. This
> fails if the JavaFX modules are not on the boot module/class path.
> 
> Instead on relying on fetching the class reference everytime it is
> needed, this change fetches it once when the JavaFX library is loaded
> and stores it in the WTF namespace.
> 
> In addition to this it was observed, that there is no attachment to the
> JVM done when calling into the filesystem. No fault was observed, but
> the JNI specs indicate, that the JNIEnv interface is only valid when
> attached.

Matthias Bläsing has updated the pull request incrementally with one additional commit since the last revision:

  Review fix: Use correct bug id

-------------

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/458/files
  - new: https://git.openjdk.java.net/jfx/pull/458/files/c9ec47c9..e1de314d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=458&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=458&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/458.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/458/head:pull/458

PR: https://git.openjdk.java.net/jfx/pull/458