Race conditions in Define Class under Java 11

[michalkurka]

We encountered exceptions in our tests when javassist is used in a multi-threaded environment:

01-24 17:22:59.044 127.0.0.1:44006       23858  FJ-3-55   ERRR: java.lang.RuntimeException: javassist.CannotCompileException: by java.lang.IllegalAccessException: class javassist.util.proxy.DefineClassHelper$JavaOther cannot access a member of class java.lang.ClassLoader (in module java.base) with modifiers "protected final"

Occurs rarely and only on Java 11. PR demonstrating the issue and a proposed fix will be submitted shortly.

[michalkurka]

Please see PR for details #243

[chibash]

I've merged the PR.
By the way, your code seems to use the old API. Java 11 requires us to use Lookup object
when loading a class file. Use ProxyFactory#createClass(Lookup).
The Lookup object can be obtained by calling MethodHandles.lookup() from somewhere
in the package that the proxy class belongs to.

[MastaP]

FYI, this concurrency issue is also reproducible on Java 6 (yes ZT still needs javassist to work with 6).
We did exactly same fix in Dec but did not have a chance to create a PR.
zeroturnaround@20de6b2