Subtle differences in System.getenv() between Windows and Linux

[Galder Zamarreno]

Hi all,

One of my colleagues discovered an intriguing difference between Linux and
Windows, in the context of GraalVM native-image, when it comes to the
returned value for System.getenv().

On windows, the native test he's encountered that a test fails with:

> Error: No instances of java.lang.ProcessEnvironment are allowed in the
image heap as this class should be initialized at image runtime

This does not happen on Linux.

The reason it fails on Windows it's because on that env the System.getenv()
method returns a ProcessEnvironment type, which happens to extend HashMap
[1]. On linux though it returns a plain map [2].

Any reason for this divergence? Is it due to historic reasons? I wondered
whether the windows and linux version of this shouldn't be more akin.

Galder

[1]
https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/windows/classes/java/lang/ProcessEnvironment.java#L69
[2]
https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/unix/classes/java/lang/ProcessEnvironment.java#L90