Using Scala 3.6.4 with Java 24 gives warnings

spamegg1 · April 13, 2025, 3:07pm

❯ scala
WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/home/spam/.sdkman/candidates/scala/3.6.4/maven2/org/scala-lang/scala3-library_3/3.6.4/scala3-library_3-3.6.4.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
WARNING: A restricted method in java.lang.System has been called
WARNING: java.lang.System::load has been called by org.jline.nativ.JLineNativeLoader in an unnamed module (file:/home/spam/.sdkman/candidates/scala/3.6.4/maven2/org/jline/jline-native/3.27.1/jline-native-3.27.1.jar)
WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
WARNING: Restricted methods will be blocked in a future release unless native access is enabled

Welcome to Scala 3.6.4 (24, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                       
scala>

Is it known, should I report it?

WojciechMazur · April 13, 2025, 3:11pm

Yes, it’s known issue, it’s going to be fixed in Scala 3.8 which would also increment the minimal version of JDK required by the compiler

dragove · April 15, 2025, 5:18am

To avoid warnings, add --sun-misc-unsafe-memory-access=allow to your jvm launch options.

for scala-cli:
//> using javaOpt --sun-misc-unsafe-memory-access=allow

for mill:
override def forkArgs: T[Seq[String]] = Seq(
“–sun-misc-unsafe-memory-access=allow”,
)

Flow · November 14, 2025, 6:48pm

Keep in mind scala.runtime.LazyVals$ also is accessed by libraries that have been compiled with an older Scala version. So even though your project may be using a Scala version which does not longer use sun.misc.Unsafe for LazyVals, your project may use libraries that where compiled with an older Scala version, which still access the legacy API provided by scala.runtime.LazyVals$that is using sun.misc.Unsafe.

To find out the culprit, you could use –sun-misc-unsafe-memory-access=debug (as per JEP 498).

For example, using scala-cli

$ scala-cli --java-opt --sun-misc-unsafe-memory-access=debug foo.sc
...
WARNING: sun.misc.Unsafe::compareAndSwapObject called by scala.runtime.LazyVals$ (file:~/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.7.4/scala3-library_3-3.7.4.jar)
	at scala.runtime.LazyVals$.objCAS(LazyVals.scala:105)
	at org.rogach.scallop.Scallop.getHelpOption$lzyINIT1(Scallop.scala:528)
	at org.rogach.scallop.Scallop.getHelpOption(Scallop.scala:521)
	at org.rogach.scallop.ScallopHelpFormatter.$anonfun$3(ScallopHelpFormatter.scala:64)
	at scala.Option.getOrElse(Option.scala:201)
	at org.rogach.scallop.ScallopHelpFormatter.getHelpLine(ScallopHelpFormatter.scala:64)
	at org.rogach.scallop.ScallopHelpFormatter.getOptionLines(ScallopHelpFormatter.scala:35)
	at org.rogach.scallop.ScallopHelpFormatter.getOptionsHelp(ScallopHelpFormatter.scala:22)
	at org.rogach.scallop.ScallopHelpFormatter.formatHelp(ScallopHelpFormatter.scala:10)
	at org.rogach.scallop.ScallopHelpFormatter.getSubcommandOptionsHelp(ScallopHelpFormatter.scala:158)
	at org.rogach.scallop.ScallopHelpFormatter.getSubcommandHelp(ScallopHelpFormatter.scala:142)
	at org.rogach.scallop.ScallopHelpFormatter.getLongSubcommandsHelp$$anonfun$1(ScallopHelpFormatter.scala:123)
	at scala.collection.immutable.List.map(List.scala:251)
	at org.rogach.scallop.ScallopHelpFormatter.getLongSubcommandsHelp(ScallopHelpFormatter.scala:122)
	at org.rogach.scallop.ScallopHelpFormatter.getSubcommandsHelp(ScallopHelpFormatter.scala:103)
	at org.rogach.scallop.ScallopHelpFormatter.formatHelp(ScallopHelpFormatter.scala:12)
	at org.rogach.scallop.Scallop.help(Scallop.scala:441)
	at org.rogach.scallop.ScallopConfBase.getHelpString(ScallopConfBase.scala:1050)
	at foo$_.<init>(foo.sc:90)
	at foo$.script$lzyINIT1(foo.sc:164)
	at foo_sc$.script(foo.sc:164)
	at foo_sc$.main(foo.sc:168)
	at foo_sc.main(foo.sc)

In this example, even though the main project uses a fairly modern Scala version (3.7.4), the Scallop library still causes this warning.

WojciechMazur · November 14, 2025, 11:36pm

Yes, that’s all correct, we’re working on tool to address this problem

nickwinlund · January 11, 2026, 10:37pm

I’m using Scala 3.7.4 (21.0.9, Java OpenJDK 64-Bit Server VM) on macOS Sequoia, with the newer Apple M4 (ARM) chip.

When I upgraded my coursier I got this warning output with scala.runtime.LazyVals. Just adding something to this conversation with no personal intent in following up. I am a lightweight Java user and I believe that I’ve only used Scala once on my MacBook Pro. After these warning messages appeared, my system’s homebrew ran “brew cleanup coursier” and therefore I think everything is fine on my end:

︎ Resource coursier–jar-launcher Verified 167.2KB/167.2KB
︎ Bottle icu4c@78 (78.2) Downloaded 32.0MB/ 32.0MB
︎ Bottle libsodium (1.0.21) Downloaded 366.0KB/366.0KB
︎ Formula coursier (2.1.25-M23) Verified 27.1MB/ 27.1MB
︎ Bottle libtasn1 (4.21.0) Downloaded 167.2KB/167.2KB
︎ Bottle nss (3.120) Downloaded 6.2MB/ 6.2MB
︎ Bottle poppler (26.01.0) Downloaded 9.6MB/ 9.6MB
==> Upgrading libarchive
3.8.4 → 3.8.5
==> Pouring libarchive–3.8.5.arm64_sequoia.bottle.tar.gz
/opt/homebrew/Cellar/libarchive/3.8.5: 65 files, 4MB
==> Running brew cleanup libarchive…
Disable this behaviour by setting HOMEBREW_NO_INSTALL_CLEANUP=1.
Hide these hints with HOMEBREW_NO_ENV_HINTS=1 (see man brew).
Removing: /opt/homebrew/Cellar/libarchive/3.8.4… (65 files, 4MB)
Removing: /Users/nick/Library/Caches/Homebrew/libarchive_bottle_manifest–3.8.4… (12.0KB)
Removing: /Users/nick/Library/Caches/Homebrew/libarchive–3.8.4… (1.6MB)
==> Upgrading sqlite
3.51.1 → 3.51.2
==> Pouring sqlite–3.51.2.arm64_sequoia.bottle.tar.gz
/opt/homebrew/Cellar/sqlite/3.51.2: 13 files, 5.3MB
==> Running brew cleanup sqlite…
Removing: /opt/homebrew/Cellar/sqlite/3.51.1… (13 files, 5.3MB)
Removing: /Users/nick/Library/Caches/Homebrew/sqlite_bottle_manifest–3.51.1… (11.4KB)
Removing: /Users/nick/Library/Caches/Homebrew/sqlite–3.51.1… (2.4MB)
==> Upgrading icu4c@78
78.1 → 78.2
==> Pouring icu4c@78–78.2.arm64_sequoia.bottle.tar.gz
/opt/homebrew/Cellar/icu4c@78/78.2: 279 files, 87.9MB
==> Running brew cleanup icu4c@78…
Removing: /opt/homebrew/Cellar/icu4c@78/78.1… (279 files, 87.9MB)
Removing: /Users/nick/Library/Caches/Homebrew/icu4c@78_bottle_manifest–78.1… (9.7KB)
Removing: /Users/nick/Library/Caches/Homebrew/icu4c@78–78.1… (32.0MB)
==> Upgrading coursier/formulas/coursier
2.1.25-M22 → 2.1.25-M23
Picked up _JAVA_OPTIONS: -Duser.home=/Users/nick/Library/Caches/Homebrew/java_cache
Downloaded 1 missing file(s) / 72
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WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/Users/nick/Library/Caches/Homebrew/java_cache/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.3.6/scala3-library_3-3.3.6.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
Picked up _JAVA_OPTIONS: -Duser.home=/Users/nick/Library/Caches/Homebrew/java_cache
WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/Users/nick/Library/Caches/Homebrew/java_cache/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.3.6/scala3-library_3-3.3.6.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
/opt/homebrew/Cellar/coursier/2.1.25-M23: 7 files, 80.1MB, built in 2 seconds
==> Running brew cleanup coursier…
Removing: /opt/homebrew/Cellar/coursier/2.1.25-M22… (7 files, 80.1MB)
Removing: /Users/nick/Library/Caches/Homebrew/coursier–2.1.25-M22.gz… (27MB)

tgodzik · January 12, 2026, 9:38am

The new implementation of lazy vals will be available in 3.8.0 version and in 3.3.8 (behind a flag). Any previous versions will have the warning.

spamegg1 · January 22, 2026, 6:49pm

I am still getting the warning in Scala 3.8.1, JDK 24

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/home/spam/.sdkman/candidates/scala/3.8.1/maven2/org/scala-lang/scala-library/3.8.1/scala-library-3.8.1.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release

Does 3.8.1 also need the flag? I think it’s -Yfuture-lazy-vals? Is that right?

//> using scala 3.8.1
//> using toolkit 0.8.0
//> using scalacOption -Yfuture-lazy-vals

WojciechMazur · January 22, 2026, 8:21pm

No, that’s a flag intended for 3.3 LTS. The warnings are due to usage dependencies using versions older then Scala 3.7. Old lazy vals implementation is still in use by the dependencies on the classpath, eg. toolkit.

See this part of release blogpost related to JDK 26 support Scala 3.8 # Other Notable Changes, especially the linked talk to Łukasz Bialy’s idea and explaining the problem - in long run we’re planing to have a dedicated JVM agent build in into major Scala build tools, that would rewrite usages of old Lazy Vals to make old dependencies usable. The plan is have it before stable before JDK 26 (when it’s starting to deny access to sun misc unsafe) and fully adapted in build tools before next LTS (JDK 29 in 2027)

That’s a complex problem that would most likely have a dedicated blogpost to explain

spamegg1 · January 22, 2026, 9:29pm

Oh I see, thanks for the explanation.
At least I don’t see it on the REPL anymore

❯ scala
Welcome to Scala 3.8.1 (24.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                
scala>