The case of primitives is slightly different

True, I had to learn to read byte code to make sense of that

The cast for primitive is even slower? Or what is the difference we are talking about here?

Not in that sense, but that the compiler will insert casts for you from int to long in stuff like loops even if you initialize a binding to be an int. So if you compare against it every iteration (such as if (< i n)), you'll end up promoting int to long every iteration. It will be slower than working with long directly, while you might think ints will always be faster

Ah ya, I just go for long and double when I can because of that. Though I don't really know how slow the cast also is.

I think that's because none of the primitive supporting functions support int, basically you can't do anything really with an int, except shove it in an array, or use it with interop Java methods that take an int.

As always, feel free to propose and vote at https://ask.clojure.org

Some of those you mention do have inline / polymorphic support

I'll see if an existing issue exist for it or add one otherwise. Ya, I think I almost find it more annoying that some of them but not all do, I always end up having to decompile to be sure. Maybe a simpler improvement could be a clearer way to document which functions does and doesn't? Is there even such a way right now? Like I saw zero? actually will, but looking at the doc/code to zero? I'm not sure how I can tell it will?

Oh... I guess it's the inlining that does it for zero?

Yes, and max at least

Perhaps do a first pass where you convert ordered collections into sets or multisets/bags first, then compare?

Perhaps we get an ID just from using a processbuilder. Let me check.

No, we need to start it to get a process id

can you explain the use case a bit?

I want to run a process in a future. The process might not terminate so I need its handle to be able to kill it.

(future (->process "echo hi")) I do not know the process id from where I call future.

But perhaps future-cancel will lead to the subprocess running in the future being killed?

You could call .destroy on the java.lang.Process, I think.

But not from where I requested the future.

(future (->process "echo hi"))
;; I have no idea what pid the process has; everything is hidden in the future

you could use a promise to pass the process back

but I imagine if we had more context we could help you pick a better design

You could check https://github.com/babashka/process

Thanks for the replies. I'll need to spend more time in the hammock it seems

There are a number of older conf talks of trying to use dataflow using datalog, but i don't think the idea ever got packaged into a production ready application...

I'm studying implement a cache mechanism by file on clojure-lsp, where if the file (especially jar content, so multiple files) didn't change we don't analyze it

So, there is this second corner case, is it possible to sha a whole jar instead of iterating on each entry and sha each one?

I never measured it, but given that you'll have to read a file in full and that IO is always the limitation, the speed of computing the checksum of a file will be limited by the speed of your IO.

Yeah, I thought the IO would be the expensive thing too, I wonder if there is any thing on java/OS side that could have this information, but it makes sense, you probably need to read the file content and then sha it

I mean, how OSs know a file changed at that time when you ls -l

Due to the modification time stored in the file system. And that's exactly what other tools use for such things. E.g. gcc, if memory serves me well, won't compile sources if their modification timestamp is less than that of the resulting object files. shadow-cljs won't compile a cljs file if the resulting js file has been created after the cljs file was changed. And so on.

hum, interesting, good to know, so maybe I can find some way to use that instead of a sha

like, first time I analyze it I could save that timestamp and then check it next time? not sure how reliable would be tho

In fact, that's definitely what you should use. :) .File/lastModified should be the right method.

Thank you! I'll do some experiments with that

Of course, a user can modify the modification timestamp for it to be in the past. But at that point, the user is deliberately shooting themselves in the foot, so it shouldn't be your concern.

yea, I wonder if there is some other case where checking the filename + lastModified of a jar would not be reliable

@UKFSJSM38 if you want fast, use blake2 or blake3

If you'd like a reference, this seems to be the right section of shadow-cljs code: https://github.com/thheller/shadow-cljs/blob/master/src/main/shadow/build/output.clj#L237-L241

for a jar for example, it may be a little tricky as user could delete a .m2 for example, but I think that would be expected to reanalyze indeed 😅

Yeah, the deletion case should also be handled - that's in the code above with .exists.

or SHA1, which is a totally, completely broken algorithm, but secure for this threat model

Awesome @U2FRKM4TW, that looks promising

@U050ECB92 thanks, didn't know about blake, is that some clojure lib or built-in function for that? (maybe java one)

agreed with @U2FRKM4TW about the larger application concern

there's a blake2 impl for java somewhere

it's a well-respected algorithm, but not built into the JVM

I found https://github.com/alphazero/Blake2b, but I thought it would be possible without an additional dep

yeah, maybe we don't need something that powerful, a simple sha1 would do the tricky if the lastModified way didn't suppress the needs

The other option is to subscribe to filesystem notification events

thanks, but since this is a one time thing after project started, probably listening would not be necessary

It seems the filename + lastModified worked liked a charm 🪄 Used a function like this to create a map with lastModified by filename:

(defn ^:private paths->checksums
  "Return a map with file's last modified timestamp by filename."
  [paths]
  (reduce
    (fn [cks path]
      (let [file (io/file path)]
        (if-let [checksum (and (shared/file-exists? file)
                               (.lastModified ^java.io.File file))]
          (assoc cks path checksum)
          cks)))
    {}
    paths))

Great! Although, I'd rename that checksum. ;)

yeah, indeed, it's not a checksum really 😅