are you using an already-existing HTTP engine, like Jetty or Tomcat?
Yes, Javalin is built on top of Jetty.
- how do virtual threads fit into a web framework?
Most JVM web frameworks (Jetty included) have a thread based request lifecyle (one thread handles one request from beginning to end). The java.lang.Threads are extremely expensive (~1mb memory), while Virtual Threads are very cheap (~0mb memory). We also have another ThreadPool for JSON streaming, and one for writing async responses. Using Virtual Threads for these things reduces overall memory pressure.
- do virtual threads make debugging more difficult? (A more general JVM question, I suppose)
Not that I know, but I've never used this in production myself.
- any performance / readability benefit, or just a coolness factor?
The alternative here is java.lang.Threads, so primarily the memory footprint. There is no readability difference. When developing, you don't see this at all.
Yes, Javalin is built on top of Jetty.
- how do virtual threads fit into a web framework?
Most JVM web frameworks (Jetty included) have a thread based request lifecyle (one thread handles one request from beginning to end). The java.lang.Threads are extremely expensive (~1mb memory), while Virtual Threads are very cheap (~0mb memory). We also have another ThreadPool for JSON streaming, and one for writing async responses. Using Virtual Threads for these things reduces overall memory pressure.
- do virtual threads make debugging more difficult? (A more general JVM question, I suppose)
Not that I know, but I've never used this in production myself.
- any performance / readability benefit, or just a coolness factor?
The alternative here is java.lang.Threads, so primarily the memory footprint. There is no readability difference. When developing, you don't see this at all.