UnsupportedOperationException at Server.handleRun

[SpriteOvO]

I'm using mill v0.10.12, and I encountered this error several days.

java.lang.UnsupportedOperationException
        at java.base/java.lang.Thread.stop(Thread.java:1705)
        at mill.main.Server.handleRun(MillServerMain.scala:209)
        at mill.main.Server.$anonfun$run$2(MillServerMain.scala:117)
        at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
        at mill.main.Server$.lockBlock(MillServerMain.scala:227)
        at mill.main.Server.$anonfun$run$1(MillServerMain.scala:98)
        at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
        at mill.main.Server$.tryLockBlock(MillServerMain.scala:235)
        at mill.main.Server.run(MillServerMain.scala:95)
        at mill.main.MillServerMain$.main(MillServerMain.scala:53)
        at mill.main.MillServerMain.main(MillServerMain.scala)

The error is always thrown after a build is completed, the build was successful. Passing --no-server to mill will suppress the error, but obviously the server will be disabled.

It seems to be thrown from

mill/main/src/mill/main/MillServerMain.scala

Line 209 in cfbafb8

try t.stop()

Any idea or workaround would be appreciated.

[lefou]

We already fixed it in main branch:

• Support Java 20 #2501

A backport seems easy enough.

[SpriteOvO]

I have applied that PR as a patch and recompiled mill locally, the error is gone. Thank you @lefou.