java - Green Threads vs Non Green Threads

Question

I'd like to understand the advantages provided by these type of threads.

• In what environments are green threads better than non-green? Some say green threads are better for multi core processors.

• Any expected behaviour problems.

Answer 1

The Wikipedia article Green Threads explains it very well.

Green threads are "user-level threads". They are scheduled by an "ordinary" user-level process, not by the kernel. So they can be used to simulate multi-threading on platforms that don't provide that capability.

In the context of Java specifically, green threads are a thing of the past. See article JDK 1.1 for Solaris Developer's Guide. (It's about Solaris, but the fact that green threads are not used anymore is valid for the usual platforms).

Green threads were abandoned in the Sun JVM for Linux as of the release of version 1.3 (see Java[tm] Technology on the Linux Platform on archive.org). That dates back to 2000. For Solaris, native threads were available from JDK 1.2. That dates back to 1998. I don't even think there ever was a green thread implementation for Windows, but I can't find a reference for that.

There are some exceptions as noted in the Wikipedia article, I gather mostly for low-power (embedded) devices.