Introduce jvm.thread.daemon and jvm.thread.state attributes

[trask]

Fixes open-telemetry/build-tools#101
Closes open-telemetry/build-tools#314

Changes

This PR does two things:

• Removes the general thread.daemon attribute and introduces jvm.thread.daemon instead
• Introduces jvm.thread.state attribute and adds it to the jvm.thread.count metric

It's definitely debatable whether these two attributes should live in the jvm.thread.* or thread.* namespace.

My primary reason for proposing that they live under jvm.thread.* is that I couldn't find anything to support these being general cross-language concepts, and JVM metric stability will depend on any attributes it uses also being marked stable.

I think we could view this like garbage collection, which is something that some other languages have, but we are not prepared to try to unify under a single set of attribute definitions prior to initial stability.

Note that while ECS defines thread.name and thread.id, they do not have anything like thread.daemon or thread.state.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• CHANGELOG.md updated for non-trivial changes.
• schema-next.yaml updated with changes to existing conventions.

[mateuszrzeszutek]

👍

[joaopgrassi]

In other hand, the "isDaemon" concept can be extracted from Python and .NET, (maybe also in other langs?) so maybe we should consider actually keeping it in the existing thread namespace? In other words, what is the drawback of keeping daemon where it is today vs adding in the jvm namespace?

If we later decide to spec it and re-use, the JVM metrics will be hurt by it.

[jsuereth]

Given Java's moves in threading models where it could be the case going forward that Java threads deviate significantly from POSIX standards, I think it makes sense to split.

Per @joaopgrassi's comments on DAEMON and python/.NET, I'm not sure we have the same meaning between them all. Would be good to do a quick comparison, but I do think isolating Java's threading model from others would be healthy at this point.

[trask]

Per @joaopgrassi's comments on DAEMON and python/.NET, I'm not sure we have the same meaning between them all. Would be good to do a quick comparison, but I do think isolating Java's threading model from others would be healthy at this point.

Java "daemon threads" == .NET "background threads"

I couldn't find any other languages that have a similar concept (other than Java, Python and .NET)

I'm personally in favor of keeping jvm.thread.daemon langauge specific, and if .NET wants to introduce similar they would probably name it .background