Explain concept of Fusion and Workers

[magware-dev]

The documentation at https://projectreactor.io/docs/core/release/reference/ is amazing, because it also explains core concepts of reactive programming.

I am currently learning project reactor and want to point out two things that I struggle with and can not find documentation for.

Documentation Issue

Fusable Interface: It shows up when using the .log() operation and also while browsing the core-code, many methods use the reactor.core.Fuseable interface (often in instanceof checks). Apparently a Publisher can be Fusable and I would like to know what that means.

Worker Interface: When looking into the Schedulers there is the reactor.core.scheduler.Scheduler.Worker interface. I found some doc about Schedulers (4.5), but no real mention of the Workers. As far as I understand, all operations request a Worker from a Scheduler to run and it looks like they play a really important role. So my suggestion is to mention them in the 4.5 Schedulers sections.

Improvement Suggestion

Add "Fusable" and "Scheduler.Worker" sections to the doc that explains those concepts.

[chemicL]

When it comes to Scheduler.Worker, I think the Javadoc is quite sufficient to grasp the idea. E.g.

/**
 * Creates a worker of this Scheduler.
 * <p>
 * Once the Worker is no longer in use, one should call dispose() on it to
 * release any resources the particular Scheduler may have used.
 *
 * It depends on the implementation, but Scheduler Workers should usually run tasks in
 * FIFO order. Some implementations may entirely delegate the scheduling to an
 * underlying structure (like an {@link ExecutorService}).
 *
 * @return the Worker instance.
 */
Worker createWorker();

For operator fusion and the significance of the Fuseable interface:

• some Javadoc explanations are provided too
• @akarnokd wrote comprehensive articles about operator fusion and repeating these would be quite an undertaking, so I'll just leave the links: Operator-fusion (Part 1), Operator fusion (part 2 - final)

Leaving the above for future seekers, but with the fact that for almost 4 years nobody picked this up, I don't think we'll find the time to explain these internals more. Perhaps someone decides to do so in the future - we can always welcome a PR :)