Are Threads in Java platform dependent?

Question

It is obvious that OS scheduling/ threading algorithms have their impact on Java threads but

can we safely say that Threads are OS/machine dependant?

If this is the case then doesn't it make Java platform dependant?

Answer 1

Yes, the details of the scheduling of threads in Java depends on the JVM implementation and (usually) on the OS implementation as well.

But the specifics of that scheduling is also not specified in the Java SE specification, only a selected few ground rules are specified.

This means that as long as the OS specific scheduling is conforming to those ground rules, it is also conforming to the JVM spec.

If your code depends on scheduling specifics that are not specified in the JVM spec, then it depends on implementation details and can not be expected to work everywhere.

That's pretty much the same situation as file I/O: if you hard-code paths and use a fixed directory separator, then you're working outside the spec and can not expect your code to work cross-platform.

Edit: The JVM implementation itself (i.e. the JRE) is platform dependent, of course. It provides the layer that allows pure Java programs to not care about the platform specifics. To achieve this, the JRE has to be paltform specific.