Make SAT thread-safe, improve performance and update SpotBugs

[wborn]

This PR makes the SAT Maven plugins thread-safe when used in parallel Maven builds.

Fixes the following theading issues:

• SpotBugs is only thread-safe when it uses the forking mode which is enabled by default but disabled in the SAT configuration.
  SpotBugs uses Apache Commons BCEL as dependency which is not thread-safe. Forking the SpotBugs execution works around this issue.
  Without forking enabled parallel builds using SpotBugs will also lock up (see Lockup in maven concurrent build, with fork=false spotbugs/spotbugs-maven-plugin#104).
• Use JVM singleton merge/summary locks for synchronizing the SAT summary report updates.
  Because multiple classloaders are used in Maven builds, it's not possible to use a static lock for synchronization in the ReportUtility Mojo.

The Mojos have also been marked as threadSafe so Maven no longer shows warnings when they are executed in parallel.

For the SpotBugs updates see:

• Spotbugs 3.1.12 release notes:
  https://github.com/spotbugs/spotbugs/blob/3.1.12/CHANGELOG.md#3112---2019-02-28
• findbugs-slf4j 1.5.0 release notes:
  https://github.com/KengoTODA/findbugs-slf4j/blob/master/CHANGELOG.md#150---2019-07-04

The errors resulting from the findbugs-slf4j upgrade have already been fixed by:

• Parameterized logging fixes openhab-core#1213
• openhab/openhab2-addons#6394

Performance has also been improved considerably by moving the HTML summary generation to an extension.
This way SAT can periodically update the HTML summary instead of continuously.
Updating the HTML summaries can take 20 seconds or more when there are many findings.

Fixes #200

---

These changes speed up both single threaded and parallel builds using SAT considerably!

Below are some openhab2-addons build results on my quad core i7-6700K (no tests because they fail, openhab/openhab2-addons#6408):

SAT version	Command	Duration	Speedup
0.8.0	mvn clean install -DskipTests	44:33 min	1.00x
0.9.0-SNAPSHOT	mvn clean install -DskipTests	23:05 min	1.93x
0.9.0-SNAPSHOT	mvn clean install -DskipTests -T 1.5C	13:31 min	3.29x

The parallel builds max out all CPUs. I can only imagine how fast a parallel build will be on a machine with 16 cores. :-)

The extension should be added to the <build> section in POMs, see wborn/openhab-addons@fe73013.

[martinvw]

Nice!

[wborn]

It would be awesome to reduce our build times by having this in a new SAT release @openhab/sat-maintainers. 😜

[Hilbrand]

Just 2 small comments.

[wborn]

Also I just noticed there are still some threading issues on Java 8 so I'll look into that too. They aren't there on Java 11 to which I try to default these days. Sometimes I switch back for other projects and then end up testing openHAB code with Java 8 too.

[Hilbrand]

Do you still want to look into the java8 issues or can I merge this?

I can only imagine how fast a parallel build will be on a machine with 16 cores. :-)

Darn. Now I got distracted browsing for a new computer 😄

[wborn]

I am still looking into how well this works for Java 8.

Yes I'm also feeling my CPU is getting dated. But they are adding more cores every year so I'll just hold on for it a bit longer to get a better deal. ;-)

[kaikreuzer]

It would be awesome to reduce our build times by having this in a new SAT release

Absolutely! I just didn't react on it before the release as I didn't want to risk anything ;-)
But now it is definitely time to benefit from this great work!

I am still looking into how well this works for Java 8.

Why? In the light of openhab/openhab-core#1287, I think it would be ok if we only support Java 11 (and keep the 2.5.x build on the current SAT version).

[wborn]

Apparently these FileChannel locks can be buggy on Java 8 and behave differently between OS-es.
So I did some more searching and found this Stack Overflow post.

It's possible get a singleton over different class loaders by always loading a class using the same class loader and a lot of reflection. I tried that and it didn't work well and all the reflection didn't make it nice code.

The other option is by just adding the singleton to the System properties. It may not be ideal but it does work on Java 8 and Java 11 and it results in less and nicer code.

[kaikreuzer]

Awesome work, @wborn!

[kaikreuzer]

New version https://github.com/openhab/static-code-analysis/releases/tag/0.9.0 has been released!

[wborn]

Thanks for making the new release! 👍