Clojurians Log v2

I would like to understand all of this Clojure error message (not just the first line)

class java.lang.Long cannot be cast to class clojure.lang.IFn (java.lang.Long
   is in module java.base of loader 'bootstrap'; clojure.lang.IFn is in unnamed
   module of loader 'app')

that's correct

it's also including module information - since Java 9, there is a module loading system in Java and the java.base module includes the core set of modules needed to start Java (other modules can be added as needed). for backwards compatibility you can still mostly ignore the module stuff but then you're loading stuff in the "unnamed" module

https://docs.oracle.com/en/java/javase/16/docs/api/java.base/java/lang/ClassLoader.html lots of info about the classloader chain here ^

I have a scenario, where my function will execute more than 10 mins which is expected, I want to stop the execution if it reaches more than 10 mins, How can I achieve it in clojure ?

What is your function doing? Listening on a socket, processing data in a loop?

My function doing caluclation on huge data, if it take more time I need to return nil , - which is my requirement

https://clojuredocs.org/clojure.core/future-cancel

(def job (future (Thread/sleep 10000)))

(future-cancel job)

cancelling threads preemptively is technically possible but risks crashing the vm if your job periodically sleeps, or waits on IO, or explicitly checks the cancellation status of its thread and exits if cancelled, future-cancel will work, but it won't do anything to a "hot loop"

(future-cancel is not using a preemptive cancellation, it's relying on one of the "cancellable" methods being called)

also the deref function (what @ expands to) takes an optional time-out number and an alternative value to return if the time-out is exceeded

which might match what you want

https://stackoverflow.com/questions/6694530/executing-a-function-with-a-timeout how about example given here/

also, on some operating systems, it might be simpler to spawn a second vm, and force that vm to shut down

the "accepted answer" is from a source I usually trust - amalloy is a smart guy I learned a lot from (we were both very active on IRC back in the day), but this answer is dangerously wrong. it uses the stop method on Thread, which is extremely dangerous and can crash the vm: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Thread.html#stop() future-cancel is safe, you just need to make sure the code you are cancelling is inside a future and that it periodically waits on IO, or calls Thread/sleep, or in some other way makes itself cancellable details here: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Thread.html#interrupt()

to be extra safe you could make sure the loop executing in the thread checks the return value of the interrupted method

how about writing similar code https://github.com/flatland/clojail/blob/master/src/clojail/core.clj#L24

again, Thread.stop is not safe

oh yeah!

what is your work doing for more than 10 minutes?

if it's IO, it can be interrupted()

My function doing caluclation on huge data, if it take more time I need to return nil , - which is my requirement

writing code like that is a lot more complex than just using a future and calling future-cancel after some time period, that code you linked is what I was referring to being unsafe because of stop

please describe the calculation?

pure math? I/O?

it calls the lambda service

then it's waiting on IO (network)

then future-cancel will work

is the Lambda the thing you're trying to stop? or are you trying to stop the thing calling the lambda?

lamda taking more time to perform calculation. my requirement is timeout if more than 10 mis

Is str/index-of the best way to see if a string contains a char (represented as a string)? I love writing if "a" in "casablanca" in Python

for a simple character check, index-of is your best bet, unlike python clojure values simplicity of syntax over intuitive / natural language like syntax

I felt like contains? sounded like it could have done the job, but it is for associative structures.

I guess you could do (contains? (set "casablanca") \a) but I don't think that really addresses your needs

and it does a lot of work you don't need to do

Agreed. But I felt like checking the value of an int was a bit... C-like?

you could also do (first (filter (set "a")) "casablanca") but that still does a lot of work you don't need to do

There’s str/includes? That has a name that indicates what it does similar to your expectation for contains?

AWS Lambda?

@endrebak85 one nitpick: it's not c-like in that (if (str/index-of "casablanca" "a") :yes :no) actually works direcly - it returns nil which if treats as false, on failure

yes

Thanks! It did not show in lein rebl for some reason

So I assumed it did not exist

@noisesmith future-cancel how to pas the minutes?

what clojure version?

True! I just assumed that it would return -1 instead of false. But that would have been extremely unclojuric.

you need something else (eg. (future (Thread/sleep (* 10 60 1000)) (future-cancel worker)))

Bad habits (assumptions?) die hard. Should have tested in the REPL.

apropos and find-doc and dir are your friends here

worker is function-name here?

why not just let the lambda timeout and be killed?

here (* 10 60 1000) turns minutes into seconds (multiply by 60), then turns seconds into ms (multiply by 1000)

worker would be the thing being cancelled

[org.clojure/clojure "1.10.3"]

where i can pass my function name

@ghadi makes a good point - lambda already has facilities to shut down after a time-out, that's the expensive resource here, it can just shut down the whole vm

Wow! Thanks for the tip about clojure.repl/find-doc

@popeyepwr you would need to use future to start it and use the return value of future, but the way @ghadi is suggesting is better since this is running in its own vm on a lambda

oh, let me search on it! all the above conversation really helped

Leveraging the queryable nature of clojure with the built in tools will serve you well. I use those constantly. After you’re comfortable with them, learn if your editor has some integrations on top of them. Many do

in C, simple type consistency is valued over semantic clarity, the jvm's comparitive complexity allows things that are closer to the intent of the code to be expressed

I frequently use find-doc and apropos and javadoc to answer questions here - I usually start with a good hunch of what should be there (or a vague memory) and let the built in introspection in the language do the rest of the work

and those tools are much more direct and helpful than google

looking up the most poetic doc string in the clojure codebase:

(ins)user=> (find-doc #"if possible")
-------------------------
clojure.core.protocols/interface-or-naive-reduce
([coll f val])
  Reduces via IReduceInit if possible, else naively.
-------------------------
clojure.core/future-cancel
([f])
  Cancels the future, if possible.
nil

Hi team how can I query current timestamp from database in Clojure project using Korma? "select current_timestamp"

(defn foo []
  (select my_table
          (fields (raw "CURRENT_TIMESTAMP"))))

@vnazaryan Korma isn't very maintained anymore I think, but I could be wrong. Instead I would recommend taking a look at #honeysql which is, if you ask me, one of the the best SQL generation libraries for Clojure,

thanks for suggestion, will take a look.

In addition to the #honeysql channel for HoneySQL, there's also a more general #sql channel for general SQL questions -- and that also tends to be where folks ask about next.jdbc which is the replacement for clojure.java.jdbc. Also #hugsql if you like your SQL in separate files, outside of your Clojure code.

is there a canonical way to parallel parse/process a large file based on a regex to split up the chunks? instaparse was overkill - all the backtracking it kept blew up the memory. I was thinking iota and reducers but each ‘chunk’ of the file is processed as a whole, not line by line, and marked with clear begin/end blocks. It’s a super regular unambiguous grammar, but not XML or such.

Whats the (better?) Clojure equivalent of a SAX parser + lots of messy Java code? I know there are several ways to parse XML, and a bunch of ways to traverse the result but haven’t tried any so far.

Probably zippers.

At work, we use clojure.data.xml (`org.clojure/data.xml`) to parse XML and clojure.zip to navigate/modify https://clojure.github.io/clojure/clojure.zip-api.html

I noticed there are two libraries: clojure.xml and clojure.data.xml . What's the difference between them?

clojure.xml is built-in but it is old/deprecated and should not be used. clojure.data.xml is a Contrib lib that is well-maintained, more modern, more feature-rich.

Ok, thanks @seancorfield

Could something like pipeline and partition-by from clojure.core.async be an idea? Read the file line by line onto a channel, partition into chunks which then get further processed in a pipeline.

It allows for a nice decoupling between reading, splitting into chunks and parsing.