I started reading Vert.x framework documentation, but i didn't understand how it works and what is a Reactor pattern, i read this article https://dzone.com/articles/understanding-reactor-pattern-thread-based-and-eve and noticed that instead of general servlet based (one request one thread) approch, Reactor pattern uses event-driven architecture where single thread named event loop takes a request put it to some sort of the job queue and provides a handler that will be executed once the task has been finished , and code in handler will be executed by this event loop, so golden rule is - don't block event loop.
What I don't understand is , from article:
Those handlers/callbacks may utilize a thread pool in multi-core environments.
So handlers use thread pool , how this pool is difference from the standard thread pool for example Servlet's container TOMCAT. How these two concepts are different from each other in case of Http server if both are using Thread pool to manage requests.
Thank in advance
Forget that DZone article. Forget the Reactor pattern. Learn Asynchronous procedure call.
There are 2 ways to split all the work in computer to parts: threads and tasks (in Java- tasks are Runnables). Tasks execute on a thread pool when they are ready. And when they are not ready, they do not occupy thread with its huge stack, and we can afford to have millions of tasks in single JVM instance, while 10000 threads in single JVM instance is problematic.
The main problem with tasks is when task needs data which is not ready (not calculated by other task, or not yet arrived via network). In the thread world, the thread waiting for data executes a blocking operation like inputsream.read(), but tasks are not allowed to do this, or they would have occupied too many threads from thread pool and all advantages of task-based programming would be lost. So tasks are augmented with mechanisms which submit that task to the thread pool exactly when all their parameters arrived. Task with such a mechanism is called asynchronous procedure call. All the event-driven architectures are variants of asynchronous procedure call: Vert.x, RxJava, Project Reactor, Akka Actors etc. They just pretend to be something original and not always talk about this.