[dullgiulio]

I don't think this is a matter of hype cycle at all. There are two things that changed:

1. Threading got much faster and lightweight. This is what Java was initially trying to work around, until it didn't have to any more.

2. The problem moved to handling as many sockets concurrently as possible. Even lightweight system threads are too heavy for scaling linearly with the number of connections (too much context-switching overhead, too much space for stack, etc.)

Green-threading has become a good idea again because we now have a kernel API that is used to multiplex a lot (but not all) I/O systemcalls.

Today Go runtime uses epoll/kqueue to read from a big bunch of sockets, whenever something new happens to any of them. This takes one system thread only.

The API model of epoll/kqueue implies some way to handle concurrency in your user code: this can either be callbacks (or async/await syntactic sugar) or green threads and CSP (channels and so on.) This is why green threading is having a comeback.

(Sorry for implying you did not read the article!)

[doctor_eval]

That's OK, lots of people fail to RTFA, but I really like reading about this stuff.

> Green-threading has become a good idea again because we now have a kernel API that is used to multiplex a lot (but not all) I/O systemcalls.

OK, that makes a lot of sense. I had to read up about how epoll is different from select/poll (that's how long it's been since I worked in C :). Clearly epoll was needed to make green threads efficient, but from what I can see, by the time epoll and friends were widespread, the pthread model was entrenched in Java.