RFR: 8335896: Source launcher should set TCCL

[Christian Stein]

On Mon, 15 Jul 2024 16:07:12 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Please review this change to set the context class loader of the current thread to the in-memory class loader when the `java` launcher is invoked in source mode. Having the source launcher set the TCCL to the in-memory classloader is benefical for scenarious depending on the TCCL being set to the application-loading loader.
>> 
>> For example, the single-argument taking [`ServiceLoader.load(Class)`](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/ServiceLoader.html#load(java.lang.Class)) method creates "a new service loader for the given service type, using the current thread's [context class loader](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Thread.html#getContextClassLoader())."
>
> src/jdk.compiler/share/classes/com/sun/tools/javac/launcher/SourceLauncher.java line 204:
> 
>> 202:             ClassLoader loader = context.newClassLoaderFor(parentLoader, firstClassName);
>> 203:             firstClass = Class.forName(firstClassName, false, loader);
>> 204:             Thread.currentThread().setContextClassLoader(loader);
> 
> Are you sure this it the right place? It might be, but seeing it in a try-catch is surprising. It should be set before the initializer for the main class runs, which might be here but checking.

Would the constructor of `MemoryClassLoader` be a better place?

Because `context.newClassLoaderFor()` has two exit-points where an instance of `MemoryClassLoader` is created.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20097#discussion_r1678950513