fix: use separator properties when running JMH

[dwalluck]

This makes the build cross-platform and fixes execution on, e.g., Windows.

[ppkarwasz]

Cool! 💯

Does it work even if the classpath contains spaces (e.g. `-Dmaven.local.repo=?

[dwalluck]

Does it work even if the classpath contains spaces (e.g. `-Dmaven.local.repo=?

It does if I add double quotes to the -cp argument. I assume that this works in both Windows and Bash.

For example, I tried: mvn -Pbenchmark "-Dmaven.repo.local=My Temp" and it worked.

Note that I think Windows can handle some mix of file separators (both \ and /), but it's the java command itself which expects ; rather than : for the classpath, I think.

[dwalluck]

Also, I tried to see if using exec:java rather than exec:exec would do some of this automatically, but I couldn't get that to work. We could probably get rid of the need to set the classpath if we created a shaded benchmarks.jar like they show in the JMH examples, but I guess this way is working.

[ppkarwasz]

Also, I tried to see if using exec:java rather than exec:exec would do some of this automatically, but I couldn't get that to work.

I tried that too and there are some classpath problems in the JVMs forked by JMH. This might be due to the way JMH forks the JVM.
Probably this could be solved with some JVM-specific arguments (e.g. -jvmArgs).

We could probably get rid of the need to set the classpath if we created a shaded benchmarks.jar like they show in the JMH examples, but I guess this way is working.

I tried that too before. The Maven Shade Plugin always shades the main artifact and has an option to also shade the test jar. This is probably not what we want to do.

[ppkarwasz]

This command line does not look very elegant, due to the fact that:

• we want ${jmh.args} to be split into words.
• we do not want the classpath to be split into words.

What would you say about passing the classpath in the CLASSPATH environment variable instead:

<environmentVariables>
  <CLASSPATH>target${file.separator}classes${path.separator}target${file.separator}test-classes${path.separator}${test.classpath}</CLASSPATH>
</environmentVariables>

[dwalluck]

Sure, this seems to work as well. I changed it.

But, I thought that the quotes were already preventing the splitting of the classpath. The JMH args were left unquoted, same as before.

[ppkarwasz]

But, I thought that the quotes were already preventing the splitting of the classpath. The JMH args were left unquoted, same as before.

The quotes should work in most normal cases, although I suspect that using " in the path of the Maven local repository on UNIX might break the configuration (the plugin uses plexus-utils to split the command line).
Using the environment variable is probably just safer.