run multiple scripts in the same GroovyScriptEngine

[sheehan]

This updates DslScriptLoader to run the batch of scripts using the same GroovyScriptEngine instance, rather than creating a new GroovyScriptEngine instance for each script. We have 20+ scripts and this change cuts the execution time in half.

I also cleaned up the file a bit and made it instance-based, rather than static.

[jenkinsadmin]

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[daspilker]

Script execution time is becoming an issue. I started to work an a similar change a few weeks ago, but stopped because changing the classpath for the script engine may introduce problems for users. Currently each script engine gets a classpath consisting of the script`s directory and the additional classpath. When sharing a script engine, there can only be one classpath. One way of solving this is to merge all classpaths as you did. But user's may rely on having separate classpaths, e.g. when using the following workspace layout:

projectA/script.groovy
projectA/Utils.groovy
projectB/script.groovy
projectB/Utils.groovy

When using a combined classpath, the helper class in projectA/Utils.groovy will hide the helper class in projectB/Utils.groovy. It pushed a test case for this to master: 0f6e0ca

This is a subtle change and probably hard to debug for users. Can we find a compatible solution? E.g. only sharing a script engine for scripts with an identical classpath?

[daspilker]

Sharing a binding between script will probably cause similar compatibility issues. Is there a reason why you share the binding?

[sheehan]

Good points. I've updated to share only for scripts with an identical classpath. Also unshared the binding.

[daspilker]

It's good that DslScriptLoader no longer relies on static methods, but do not move any methods. Leave these where they are and mark them as deprecated. Then we can remove them eventually.

[sheehan]

That makes sense. The order is fixed now.

[daspilker]

Cool. Can't wait to try this in production. I merged your commits manually.