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Limit exposure to ConcurrentModificationException when sys props are replaced or mutated #22180

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merged 2 commits into from
Dec 20, 2024
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Limit exposure to ConcurrentModificationException when sys props are replaced or mutated #22180

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705c33c
Limit exposure to ConcurrentModificationException when sys props are …
jtjeferreira Dec 10, 2024
31690d4
improve javaBootClassPath lazy evaluation
jtjeferreira Dec 10, 2024
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16 changes: 12 additions & 4 deletions compiler/src/dotty/tools/dotc/config/PathResolver.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -36,17 +36,25 @@ object PathResolver {
/** Values found solely by inspecting environment or property variables.
*/
object Environment {
private def searchForBootClasspath = (
systemProperties find (_._1 endsWith ".boot.class.path") map (_._2) getOrElse ""
)
private def searchForBootClasspath = {
import scala.jdk.CollectionConverters.*
val props = System.getProperties
// This formulation should be immune to ConcurrentModificationExceptions when system properties
// we're unlucky enough to witness a partially published result of System.setProperty or direct
// mutation of the System property map. stringPropertyNames internally uses the Enumeration interface,
// rather than Iterator, and this disables the fail-fast ConcurrentModificationException.
val propNames = props.stringPropertyNames()
propNames.asScala collectFirst { case k if k endsWith ".boot.class.path" => props.getProperty(k) } getOrElse ""
}
Comment on lines +39 to +48
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I tried to understand why this fallback exists, but I landed here and that was a dead end. Maybe we could just remove this code and do

def javaBootClassPath: String = propOrElse("sun.boot.class.path", "")

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@SethTisue SethTisue Dec 20, 2024 •
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probably? for now let's go with the tried-and-true

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I see that this is what I asked in my other comment: it is because scala 2 runner supplied scala.boot.class.path. It would be worth revisiting what is supported under scala-cli. There is still -bootclasspath option. In scala 2, -nobootcp meant don't use -Xbootclasspath and don't supply scala.boot.classpath. Modern class loader hierarchy is quite different. I always use -nobootcp in scala 2.


/** Environment variables which java pays attention to so it
* seems we do as well.
*/
def classPathEnv: String = envOrElse("CLASSPATH", "")
def sourcePathEnv: String = envOrElse("SOURCEPATH", "")

def javaBootClassPath: String = propOrElse("sun.boot.class.path", searchForBootClasspath)
//using propOrNone/getOrElse instead of propOrElse so that searchForBootClasspath is lazy evaluated
def javaBootClassPath: String = propOrNone("sun.boot.class.path") getOrElse searchForBootClasspath
Comment on lines +56 to +57
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this change is a second commit, that is not part of the initial one that I was porting. But I think this improvement makes sense.

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This is not an improvement. propOrElse("user.dir", ???). This is the property that was removed at some point, I don't remember the details or naming. I see it is in JDK 8 but not now.

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oh, scala 2 at least supplied scala.boot.class.path as a workaround.

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This is not an improvement

propOrElse is not lazy like in scala2, right? So this was an improvement...

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@som-snytt som-snytt Dec 20, 2024 •
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That's a shame. Edit: I meant the usual lack of code sharing, not the improvement!


def javaExtDirs: String = propOrEmpty("java.ext.dirs")
def scalaHome: String = propOrEmpty("scala.home")
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