[jimmaswell]

That sounds like the runtime has more constraints thus it can make more assumptions, not less constraints, while the OS one must be more general.

[lilactown]

It depends on your perspective.

The OS one has more _requirements_ (the number of "it must do..." is much higher), which constrains it's design space much more. I think you can call that as "having more constraints" because it must meet more needs to be even viable as a solution.

The number of requirements for JVM threads is much lower, thus less constraining, allowing it more freedom to implement solutions that can meet its narrower window of features.

[clhodapp]

Constraints on the user free the platform. Freedoms for the user constrain the platform.

If you are interested in someone pontificating about this at length, see https://youtu.be/GqmsQeSzMdw