Clojure Q&A - Recent questions tagged jvm

Is RT.longCast() missing an overload for char?

Thu, 31 Jul 2025 11:02:56 +0000

This code resorts to reflection:

(long (char \x))

call to static method longCast on clojure.lang.RT can't be resolved (argument types: char).

Casting to int does not trigger this reflection warning, as RT.intCast(char) exists.

It seems to me there should be a RT.longCast(char) as well?

Is a bytecode file generated after the Clojure code compilation?

Tue, 27 Jun 2023 21:23:34 +0000

I mean, is the generated bytecode directly fed to the JVM, or a .class file is created and the bytecode is saved there? And also, if a file is generated, is it generated for every evaluated expression?

Type hints getting ignored, reverting to java.lang.Object

Sun, 02 May 2021 01:56:00 +0000

  (deftype l [^java.util.List x])
  (use '[clojure.reflect :as r])
  (:members (r/reflect (l. `())))

Despite the type-hints of java.util.List, on reflection x seems to always be an Object

Have been specifically trying to get an optaplanner example working in 100% clojure https://github.com/joinr/optaplanner-clj/tree/163d326a6433b88ca9811e33d30758ceff42b91f . The code is evaluating but this error keeps occurring on running (solve (->problem))

Unhandled java.lang.IllegalStateException The solutionClass (class optaplanner_clj.data.TimeTable) has a
PlanningEntityCollectionProperty annotated member (public final
java.lang.Object optaplanner_clj.data.TimeTable.lessonList) that does
not return a Collection or an array.

is It possible to implement a label/goto mechanism in clojure

Fri, 30 Apr 2021 08:49:38 +0000

Apparently the JVM has a label/goto mechanism. Would it be possible to add such a capability to the Clojure language?

I suppose there are two questions which could be addressed 100% independently.
1. whether it is theoretically possible. i.e., to the JVM instructions really permit such a Clojure primitive at all. Perhaps I'm mistaken, and it is really not possible.
2. whether the core Clojure maintainers can be convinced of the merits of the request.

In general goto is useful in machine generated code, not so much in human written code.

I have at least three use cases where I'd like to have such a mechanism.

serialization of deterministic finite automata
serialization of discrimination nets
translation of Knuth style algorithms into Clojure from Art of Computer Programming.

I know that lots of people might respond with philosophical arguments about why you shouldn't use goto. I hope to avoid such a discussion here.

One possibility which seems reasonable to me would be a Clojure primitive similar to the Common Lisp prog although the ability to bind variables is not really necessary, as it could easily be implemented by the user by using let with some macrology.

How to locate a function when debugging?

Mon, 13 Apr 2020 05:30:06 +0000

Our server is experiencing memory leaking. As to investigate what happened, I used jmap to dump JVM and got the following file:

No dump file specified
 num     #instances         #bytes  class name (module)
-------------------------------------------------------
   1:        904887       79630056  java.lang.reflect.Method (java.base@13.0.2)
   2:        935204       50874608  [Ljava.lang.Object; (java.base@13.0.2)
   3:        889710       47099400  [B (java.base@13.0.2)
   4:         85795       26006880  [C (java.base@13.0.2)
   5:        518846       22286056  [I (java.base@13.0.2)
   6:        781108       18746592  java.lang.String (java.base@13.0.2)
   7:        382891       15315640  java.math.BigInteger (java.base@13.0.2)
   8:        370774       14830960  java.math.BigDecimal (java.base@13.0.2)
   9:        153329       12266320  java.lang.reflect.Constructor (java.base@13.0.2)
...
 152:          1665         146520  java.util.regex.Pattern (java.base@13.0.2)
 153:          3638         145520  com.newrelic.agent.deps.org.objectweb.asm.tree.LdcInsnNode
 154:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48879
 155:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48881
 156:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48883
 157:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48885
 158:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48887
 159:          9043         144688  exchange.api.restful.orders$fn__48874$fn__48892
 160:          9006         144096  java.util.Formatter$Flags (java.base@13.0.2)
 161:          8973         143568  java.util.concurrent.atomic.AtomicBoolean (java.base@13.0.2)
...
 600:           296           7104  java.math.MathContext (java.base@13.0.2)
 601:           221           7072  java.lang.invoke.BoundMethodHandle$Species_L (java.base@13.0.2)
 602:           221           7072  java.lang.invoke.LambdaForm$NamedFunction (java.base@13.0.2)
 603:           438           7008  clojure.core$distinct$step__6413
 604:           291           6984  taoensso.nippy$read_kvs_into$fn__36561
 605:           218           6976  sun.nio.fs.UnixPath (java.base@13.0.2)
 606:           218           6976  taoensso.carmine.protocol.EnqueuedRequest
 607:           173           6920  java.nio.channels.ClosedChannelException (java.base@13.0.2)
 608:           431           6896  clojure.core.async.impl.ioc_macros$return_chan$fn__21752
 609:           287           6888  javax.management.ImmutableDescriptor (java.management@13.0.2)
...

So as you might interpret from it, it is an API service. And judging from the number of instances, I decided exchange.api.restful.orders$fn__48874$* is bad. (Or I am wrong. My colleague suggested redis went wrong.)

But here then goes the question: which function/api is it? How can I locate it?

Can we use AppCDS to speed up app start?

Tue, 06 Aug 2019 19:36:10 +0000

I’ve been reading the Oracle docs about AppCDS and wondered if for the core functions in clojure we could use AppCDS to snapshot them?

https://docs.oracle.com/javase/8/docs/technotes/guides/vm/class-data-sharing.html

Thanks,

Sam