.map() and .chain() question

[geniusit]

Hi,

which approach is beter? In term of perf, mutiny standard, mutiny philosophy...

@GET
    @Produces(MediaType.TEXT_PLAIN)
    @Path("/chain")
    public Uni<String> chain() {
        
        return
                Uni
                        .createFrom()
                        .item("aRandomValue")
                        .invoke(value -> log.info("value : {}", value))
                        .chain(() -> Uni.createFrom().item("CHAIN"));
        
    }

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    @Path("/map")
    public Uni<String> map() {
        
        return
                Uni
                        .createFrom()
                        .item("aRandomValue")
                        .invoke(value -> log.info("value : {}", value))
                        .map(_ -> "MAP");
    }

Which one do you suggest me to use ? Every day I face this situation and I never know which approach is best?
(I know this code isn't reactive, it's just a simplified representation of the situation I try to show)

[jponge]

These methods are shortcuts:

• map is onItem().transform(item -> value) and is used to perform a transformation without I/O involved (e.g., extracting some piece of JSON from a HTTP response)
• chain is onItem().transformToUni(item -> uni) and is used to perform a transformation with I/O (e.g., you take a value and use it to perform a HTTP client request, and the HTTP response becomes the next value in the pipeline, etc).

[weltonrodrigo]

Should CPU bound operations use chain or map? Like resizing a byte[] containing a jpeg (no disk operation involved)?

[jponge]

map should be used, as explained above

[weltonrodrigo]

Thank you for the answer. To clarify, I was trying to make sense of slow operations. The resizing operation I was referring to take 150ms. Would that be a blocking operation? Or block is really only I/O?

[geniusit]

My suggestion is always try to use non blocking api. In your case, even if the default max time allowed to block by the event loop is 2s, I suggest you to read this. It's safer not to do your resizing operation in the event loop. But it's not the subject of this discussion. But yes, to me it's a blocking operation and should be done in the executor thread pool

[jponge]

150ms is indeed in the range of CPU-bound operations that'd be better outside of an event-loop