The article explains that the primary benefit of user-mode green-thread fibers is not switching speed, but that they are much cheaper than OS threads, so you can have many more of them. The costs are paid in memory usage and also the operating system also has to do considerable bookkeeping for threads.
However, Netty has offered strong support for callback style IO under the JVM for a long time. This effectively allows the same efficiencies. Of course it is also possible to do without Netty. Therefore the real advantage of Loom user-mode threads and co-routines is syntactical programming convenience. That's the real innovation in Loom!
However, Netty has offered strong support for callback style IO under the JVM for a long time. This effectively allows the same efficiencies. Of course it is also possible to do without Netty. Therefore the real advantage of Loom user-mode threads and co-routines is syntactical programming convenience. That's the real innovation in Loom!