Java already had M:N threads in the early days, aka green threads, because the JVM and Java specifications did not assert what kind of threading was to be provided.
replyThus most JVM implementations had a mix of red (1:1:) and green (M:N) threads, eventually only red threads were kept in the surviving implementations.
With Project Loom now both models are officially supported and part of the specification.
Yeah I've heard of the Java 1-2 greenthreads, but supposedly those were M:1, ie you could only run them on one core. At least this SCO release note linked from Wikipedia says that: https://www.sco.com/developers/java/j2sdk122-001/ReleaseNote... And the pros are more about compatibility than performance
replyHow have you found a SCO note, which never did nothing relevant for Java?
replyHere from Oracle, as historically taken from Sun documentation for JDK 1.1.
=> Many-to-Many Model (Java on Solaris--Native Threads)
https://docs.oracle.com/cd/E19455-01/806-3461/6jck06gqk/inde...
I think there's a naming confusion here. You said "M:N threads, aka green threads". However, your linked document clarifies that "green threads" are the M:1 threads that "[do] not exploit multiprocessors" (see the "Green Threads" parenthetical in the first subheading). It is interesting that JDK 1.1 also had an M:N threading model, but that's not what people usually mean by green threads.
replyI always understood it like that, however maybe it is on me, when reading this with more detail.
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