Clojure Q&A - Questions without answers in Contrib libs

`pipeline-blocking` uses `thread` internally instead of `io-thread`

Wed, 29 Oct 2025 15:54:00 +0000

pipeline-blocking is explicitly meant for blocking operations (implying I/O). However, internally it uses thread rather than io-thread for processing: https://github.com/clojure/core.async/blob/master/src/main/clojure/clojure/core/async.clj#L637-L640.

Since 1.9.829-alpha2 this has practical implications, as only io-thread will utilize virtual threads, when available.

Can this be fixed / changed?
If not, can an explicit pipeline-io (or similar) function be added to support this use case?

Thanks

Choosing between core.async pipelines

Sun, 26 Oct 2025 22:19:12 +0000

It's no longer clear what kind of pipeline is suitable for what kind of task in core.async.

Previously, my understanding was that anything I/O-bound should go into pipeline-blocking, while CPU-bound tasks went into regular (i.e. :compute) pipeline. But a while back :compute pipelines were changed to use threads instead of go-blocks. And now, with the introduction of virtual threads, pipeline-async seems like the right choice for I/O-bound tasks.

It seems that workloads are being classified into one of three types: :compute, :io, and :mixed. Is :async meant to be the equivalent of :io, and :blocking the equivalent of :mixed? I don't think that's original semantics, but it seems to be the mapping now.

Allocation churn on generators

Tue, 07 Oct 2025 21:16:10 +0000

When generating moderately large values there is some LazySeq churn that could be avoided. For example, the following snippet allocates over 15GB (measured with async-profiler):

(core/let [g (vector (not-empty string-alphanumeric) 1000 5000)]
  (time
   (dotimes [seed 50]
     (dorun (generate g 100 seed)))))

The pattern of generating multiple (increasingly larger) values is common with quick-check (via deftest et al).

Many generators are built on top of choose, and there is an opportunity to reduce churn by special casing shrink-int for longs (which should be the common case compared to big ints).

I have a patch that decreases total allocations of the repro above by ~15% and speed up the run time by ~25% (measured on jdk 25, with -Xmx512m -XX:+UseSerialGC to decrease variance). Happy to share it.

`create-basis` silently accepts missing aliases

Tue, 10 Jun 2025 00:57:37 +0000

In this scenario, the alias for create-basis was incorrect, preventing security deps overrides from being applied. For 2 years clojars was deployed with these vulnerable deps.

In this case, I proposed to inline the alias into :deps. However there may be other scenarios where a tools.deps change might be helpful to catch these mistakes earlier, for example a warning or error.

core.async go block error with clojure 1.12 method values

Tue, 25 Feb 2025 19:17:23 +0000

I haven't seen this reported.

(Long/.toString 123) ;;works
(a/<!! (a/thread (Long/.toString 123))) ;;works
(a/go (Long/.toString 123)) ;;error

Note: The following stack trace applies to the reader or compiler, your code was not executed.

CompilerException Syntax error macroexpanding a/go at (1:1). {:clojure.error/phase :macro-syntax-check, :clojure.error/line 1, :clojure.error/column 1, :clojure.error/source "NO_SOURCE_PATH", :clojure.error/symbol a/go}
ExceptionInfo No matching method: .toString for class: class java.lang.Long and arity: 1 {:method .toString, :class java.lang.Long, :argc 1, :file "NO_SOURCE_PATH", :column 7, :line 1}
	clojure.tools.analyzer.passes.jvm.validate/validate-call (validate.clj:127)
	clojure.tools.analyzer.passes.jvm.validate/validate-call (validate.clj:87)
	clojure.tools.analyzer.passes.jvm.validate/eval4802/fn--4803 (validate.clj:137)
	clojure.lang.MultiFn.invoke (MultiFn.java:229)
	clojure.tools.analyzer.passes.jvm.validate/validate (validate.clj:265)
	clojure.tools.analyzer.passes.jvm.validate/validate (validate.clj:240)
	clojure.lang.Var.invoke (Var.java:386)
	clojure.tools.analyzer.passes/compile-passes/fn--3424/fn--3429 (passes.clj:167)
	clojure.tools.analyzer.passes/compile-passes/fn--3424/fn--3431 (passes.clj:169)
	clojure.tools.analyzer.passes/compile-passes/fn--3424/fn--3431 (passes.clj:169)
	clojure.tools.analyzer.passes/compile-passes/fn--3424/fn--3431 (passes.clj:169)
	clojure.core/partial/fn--5929 (core.clj:2648)

unable to use add-lib on io.github.borkdude/grasp

Fri, 17 Jan 2025 14:15:15 +0000

repro:

user=> (add-lib 'io.github.borkdude/grasp {:mvn/version "0.1.4"})
Execution error (ExceptionInfo) at clojure.tools.deps.interop/invoke-tool (interop.clj:81).
Could not find artifact org.clojure:clojure:jar:1.11.0-rc1

This seems strange to me. The deps edn of grasp: https://github.com/borkdude/grasp/blob/master/deps.edn

{:deps {org.babashka/sci {:mvn/version "0.3.2"}}
 :aliases {:native {:jvm-opts ["-Dclojure.compiler.direct-linking=true"]
                    :extra-deps {org.clojure/clojure {:mvn/version "1.10.2-alpha3"}
                                 org.clojure/tools.cli {:mvn/version "1.0.194"}}}
           :test {:extra-paths ["test"]
                  :extra-deps {org.clojure/clojure {:mvn/version "1.11.0-rc1"}
                               cognitect-labs/test-runner
                               {:git/url "https://github.com/cognitect-labs/test-runner"
                                :sha "cb96e80f6f3d3b307c59cbeb49bb0dcb3a2a780b"}}
                  :main-opts ["-m" "cognitect.test-runner"]}}}

It's surprising to me that deps in the :test alias would cause issues.

EDIT: seems to work now. Here's the stacktrace from a socket repl where i first encountered it

user=> (add-lib 'io.github.borkdude/grasp {:mvn/version "0.1.4"})
Execution error (ExceptionInfo) at clojure.tools.deps.interop/invoke-tool (interop.clj:81).
Could not find artifact org.clojure:clojure:jar:1.11.0-rc1
user=> nil
user=> (pst)
ExceptionInfo Could not find artifact org.clojure:clojure:jar:1.11.0-rc1 {:via [{:type clojure.lang.ExceptionInfo, :message "Could not find artifact org.clojure:clojure:jar:1.11.0-rc1", :data {:lib org.clojure/clojure, :coord {:mvn/version "1.11.0-rc1", :deps/manifest :mvn, :dependents [io.github.borkdude/grasp], :parents #{[io.github.borkdude/grasp]}}}, :at [clojure.tools.deps.extensions.maven$get_artifact invokeStatic "maven.clj" 167]}], :trace [[clojure.tools.deps.extensions.maven$get_artifact invokeStatic "maven.clj" 167] [clojure.tools.deps.extensions.maven$get_artifact invoke "maven.clj" 155] [clojure.tools.deps.extensions.maven$eval1225$fn__1228 invoke "maven.clj" 178] [clojure.lang.MultiFn invoke "MultiFn.java" 244] [clojure.tools.deps$download_libs$fn__802$fn__803 invoke "deps.clj" 466] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 428] [clojure.lang.AFn applyToHelper "AFn.java" 156] [clojure.lang.RestFn applyTo "RestFn.java" 135] [clojure.core$apply invokeStatic "core.clj" 671] [clojure.core$bound_fn_STAR_$fn__5837 doInvoke "core.clj" 2020] [clojure.lang.RestFn invoke "RestFn.java" 400] [clojure.lang.AFn call "AFn.java" 18] [java.util.concurrent.FutureTask run "FutureTask.java" 317] [java.util.concurrent.ThreadPoolExecutor runWorker "ThreadPoolExecutor.java" 1144] [java.util.concurrent.ThreadPoolExecutor$Worker run "ThreadPoolExecutor.java" 642] [java.lang.Thread run "Thread.java" 1583]], :cause "Could not find artifact org.clojure:clojure:jar:1.11.0-rc1", :data {:lib org.clojure/clojure, :coord {:mvn/version "1.11.0-rc1", :deps/manifest :mvn, :dependents [io.github.borkdude/grasp], :parents #{[io.github.borkdude/grasp]}}}}
	clojure.tools.deps.interop/invoke-tool (interop.clj:81)
	clojure.tools.deps.interop/invoke-tool (interop.clj:41)
	clojure.repl.deps/add-libs (deps.clj:48)
	clojure.repl.deps/add-lib (deps.clj:59)
	clojure.repl.deps/add-lib (deps.clj:59)
	user/eval310956 (NO_SOURCE_FILE:320)
	user/eval310956 (NO_SOURCE_FILE:320)
	clojure.lang.Compiler.eval (Compiler.java:7700)
	clojure.lang.Compiler.eval (Compiler.java:7655)
	clojure.core/eval (core.clj:3232)
	clojure.core/eval (core.clj:3228)
	user/eval257807/fn--257810 (NO_SOURCE_FILE:8)

clojure.data.priority-map's IKVReduce implementation doesn’t support `reduced`

Sat, 28 Sep 2024 23:52:55 +0000

Hi folks!

Just a heads-up that clojure.data.priority-map’s IKVReduce implementation doesn’t support reduced.

The current implementation (v1.2.0, 2024-02-19):

clojure.core.protocols/IKVReduce
(kv-reduce [this f init]
  (if keyfn            
    (reduce-kv (fn [a k v] (reduce (fn [a v] (f a v (item->priority v))) a v))
      init priority->set-of-items)
    (reduce-kv (fn [a k v] (reduce (fn [a v] (f a v k)) a v))
      init priority->set-of-items)))

But the nested reduce means that something like this’d be needed:

(defn- convey-reduced [x] (if (reduced? x) (reduced x) x))

clojure.core.protocols/IKVReduce
(kv-reduce [this f init]
  (if keyfn            
    (reduce-kv (fn [a k v] (reduce (fn [a v] (convey-reduced (f a v (item->priority v))) a v)))
      init priority->set-of-items)
    (reduce-kv (fn [a k v] (reduce (fn [a v] (convey-reduced (f a v k)) a v)))
      init priority->set-of-items)))

Note that the issue affects only (reduce-kv a-priority-map …), not (reduce a-priority-map …).

Thanks, cheers! :-)

Warn about user.clj during build compilation

Wed, 28 Feb 2024 13:20:46 +0000

We’ve had a few cases where people encountered issues due to the existence of user.clj during uberjar building with tools.build.

Because user loads early, anything it loads is not (typically) reloaded during compilation, which can lead to some namespaces not being compiled.

Should maybe warn if user is on classpath or even actively recompile with something like

(binding [*compile-files* true] (require 'user :reload-all))

Abstract env var reading in tools.deps

Sat, 16 Sep 2023 02:35:57 +0000

I have a Cursive user wanting to use the CLOJURE_CLI_ALLOW_HTTP_REPO env var. Since Cursive invokes tools.deps in-process, there's no way for me to set an env var in the current process. deps.clj has a nice abstraction for this - would it be possible to use this or something similar for tools.deps too? I assume this problem will affect any process using tools.deps as a library.

switch tools.build to pull from jars rather than exploding onto disk

Tue, 29 Aug 2023 20:49:38 +0000

Following on from https://ask.clojure.org/index.php/10854/getting-an-error-with-tools-build-uberjar?show=10854#q10854

Jars are case-sensitive. This means that an uberjar can have a file named license and LICENSE/epl.txt simultaneously inside them. But if you explode these to disk when building an uberjar in a file system that is case-sensitive (in particular, OSX), you can an error along the lines of

Execution error (ExceptionInfo) at clojure.tools.build.tasks.uber/explode1 (uber.clj:166).
Cannot write META-INF/license/LICENSE.aix-netbsd.txt from io.grpc/grpc-netty-shaded as parent dir is a file from another lib. One of them must be excluded.

The solution to this is to track down the conflicting files and add them to exclusions. But often this can be tedious if the single file you want ot exclude license exists and the error message is about one of several files that conflicts LICENSE/epl.txt.

The error is annoying also because these files can sit together just fine in an uberjar, but not in their temporary location on disk. It would be nice if the uberjar could just pull files from each jar rather than copy them onto disk in an intermediate step.

Tools deps perform sanity checking on deps.edn file

Thu, 23 Mar 2023 19:46:07 +0000

Peform validation of deps.edn files, providing useful error messages and information about misspelled keywords, invalid types, valid data in the wrong location.

Some motivating examples:

misspelled keywords:
:overide-deps
https://groups.google.com/g/clojure/c/g-Gy3Q7jHfk

including valid options in incorrect locations

:jvm-opts in the top level
https://app.slack.com/client/T03RZGPFR/C6QH853H8

invalid data types in valid edn files:

{:deps :org.clojure/tools.reader {:mvn/version "1.2.3"} org.clojure/tools.reader {mvn/version "1.2.3"}}

first dep has a keyword where a symbol should be present
second dep has a symbol where a keyword should be present

For implementation
spell-spec is a great tool to do this
https://github.com/bhauman/spell-spec

related JIRA ticket
https://clojure.atlassian.net/browse/TDEPS-238

Document that clojure.data.int-map is sorted

Fri, 17 Mar 2023 08:58:14 +0000

Recently a question about it was asked on Slack.

This DIMAP-4 Jira ticket has made the map and the set deliberately sorted, but it was never mentioned in the docs.
Seems like it could be explicitly mentioned in the docstrings?

`intersection` and `union` do not support `nil` punning

Tue, 31 Aug 2021 16:51:39 +0000

This is for org.clojure/data.int-map v 1.0.0.
At the same time clojure.set/intersection and clojure.set/union handle the case well.

(ns sandbox
  (:require
   [clojure.data.int-map :as int-map]
   [clojure.set]))

(clojure.set/intersection #{1 3} #{1 2 3}) ; => #{1 3}
(clojure.set/intersection #{1 3} nil) ; => nil
(clojure.set/intersection nil #{1 2 3}) ; => nil

(int-map/intersection (int-map/int-set #{1 3}) (int-map/int-set #{1 2 3})) ; => #{1 3}
(int-map/intersection (int-map/int-set #{1 3}) nil) ; => NullPointerException
(int-map/intersection nil (int-map/int-set #{1 2 3})) ; => NullPointerException

(clojure.set/union #{1 3} #{2}) ; => #{1 3 2}
(clojure.set/union #{1 3} nil) ; => #{1 3}
(clojure.set/union nil #{2}) ; => #{2}

(int-map/union (int-map/int-set #{1 3}) (int-map/int-set #{2})) ; => #{1 2 3}
(int-map/union (int-map/int-set #{1 3}) nil) ; => NullPointerException
(int-map/union nil (int-map/int-set #{2})) ; => NullPointerException

`Ambiguous method signature for method: close` thrown where clojure.core wouldn't

Thu, 01 Apr 2021 17:15:51 +0000

The following code will throw an exception:

(ana.jvm/analyze '(reify
                    java.io.Closeable
                    (close [_])
                    example.foo/EventClient
                    (close [_])))
                    ;; => clojure.lang.ExceptionInfo: Ambiguous method signature for method: close

...where example.foo/EventClient is a a real, resolvable defprotocol that does in fact define a close [_] method.

Here is a reproducible patch that can be applied over https://github.com/clojure/tools.analyzer.jvm/commit/f00d92317307c3e9e326fd99d337292925dc9db1 :

https://gist.githubusercontent.com/vemv/ae450c380ac96683bc06275323e7e322/raw/91ad4b60502b32f4f57bd0d5707bcf51740f8e7b/gistfile1.patch

Can core.match LiteralPattern emit more specialized code?

Tue, 01 Dec 2020 07:29:48 +0000

Hello,
Looking at the code emitted by core.match, I see that literals are always compared using =.
While it works, wouldn't it be faster to specialize equality for different literals, such as:

 (number? l) `(and (number? ~ocr) (== ~l ~ocr))
 (keyword? l) `(identical? ~l ~ocr)
 (nil? l) `(nil? ~ocr)
 (true? l) `(true? ~ocr)
 (false? l) `(false? ~ocr)
 (string? l) `(.equals ~l ~ocr)

(snippet added to LiteralPattern cond.

Crude benchmarks show it's faster than = and all the tests pass, too.

Think this warrants a patch?

Form emitting by cljs.analyzer

Wed, 05 Aug 2020 10:51:06 +0000

Hi!
I want to write a code to code compiler for both Clojure and ClojureScript.
So I need something like clojure.tools.analyzer.passes.js.emit-form/emit-form, but tools.analyzer.js is abandoned and cljs.analyzer can't emit clojure form from AST.

How can I write my code transformation in terms of AST with tools.analyzer.jvm and cljs.analyzer?
Should I use both cljs.analyzer and clojure.tools.analyzer.passes.js.emit-form/emit-form?

Can I use clojure.tools.analyzer.ast/walk with cljs.analyzer?

How to use passes in terms of tools.analyzer with cljs.analyzer? I think it's impossible.

Let RoseTree satisfy (implement) Datafiable

Thu, 02 Jul 2020 18:36:54 +0000

I think for debugging it would be awesome to be able to navigate through the rose trees.