A prototype project which tries to implement Vaadin Blocking dialogs using the Java Project Loom. Uses Vaadin Boot. Requires Java 20+.
Read Vaadin and Blocking Dialogs on why this is such a hard thing to do.
Simply run Main.java main() method from your IDE. Make sure to have the following JVM
arguments when launching Main.java (in Intellij: edit launch configuration, modify options, add VM options):
--enable-preview --add-opens java.base/java.lang=ALL-UNNAMED
The reason is that we're hacking deep into virtual threads and we need access to JVM internal stuff.
See the live demo running on v-herd.
This is not even alpha quality. If it works, it works just by a random coincidence. I'm just hacking deep into virtual threads, without really knowing what I'm really doing. Prototype quality.
I don't even know whether this works on any other Java than the one I'm running (Eclipse Temurin JDK 20). The project may fail on other JVMs. Or maybe not :)
This is obviously bloody dark magic.
Please see the Vaadin Boot documentation on how you run, develop and package this Vaadin-Boot-based app.
First, read Oracle article on virtual threads, to familiarize yourself with the terminology: virtual thread, carrier thread, mounting and unmounting.
The main idea is to configure JVM to somehow make virtual threads mount to the Vaadin UI threads and run from
there. Of course there's no special UI thread per se, there are only threads currently holding the Vaadin session lock.
To run a Runnable in Vaadin UI 'thread' you call UI.access().
Project Loom allows us to run code in a virtual thread. Virtual thread runs the code as a series
of continuations, each continuation running a piece of code until it blocks. Continuation is ultimately a Runnable.
We'll run Continuation Runnables via UI.access().
I repeat. This is obviously bloody dark magic.
As it turns out, it's possible to also implement a so-called generator using this technique.
See the Iterators.fibonacci() for more details:
public final class Iterators {
public static Iterator<Integer> fibonacci() {
return iterator(y -> {
int t1 = 0;
int t2 = 1;
while (true) {
y.yield(t1);
final int sum = t1 + t2;
t1 = t2;
t2 = sum;
}
});
}
}Please read Java Generators on how this works.