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SI-7775 Harden against the shifting sands of System.getProperties

If another thread writes a new system property (which can happen
in pretty innocuous code such as `new Date`!), the compiler startup
could fail with a `ConcurrentModificationException` as it iterated
all bindings in the properties map in search of a boot classpath
property for esoteric JVMs.

This commit uses `Properties#getStringProperties` to get a snapshot
of the keys that isn't backed by the live map, and iterates these
instead. That method will also limit us to bindings with String
values, which is all that we expect.
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1 parent 7b351dc commit 9d5ed33ef9b503f20506dbe3e410960069a99d0a @retronym retronym committed Aug 23, 2013
Showing with 23 additions and 2 deletions.
  1. +6 −2 src/compiler/scala/tools/reflect/WrappedProperties.scala
  2. +17 −0 test/files/run/t7775.scala
@@ -26,9 +26,13 @@ trait WrappedProperties extends PropertiesTrait {
override def envOrElse(name: String, alt: String) = wrap(super.envOrElse(name, alt)) getOrElse alt
override def envOrNone(name: String) = wrap(super.envOrNone(name)).flatten
- def systemProperties: Iterator[(String, String)] = {
+ def systemProperties: List[(String, String)] = {
import scala.collection.JavaConverters._
- wrap(System.getProperties.asScala.iterator) getOrElse Iterator.empty
+ wrap {
+ val props = System.getProperties
+ // SI-7269 Be careful to avoid `ConcurrentModificationException` if another thread modifies the properties map
+ props.stringPropertyNames().asScala.toList.map(k => (k, props.get(k).asInstanceOf[String]))
+ } getOrElse Nil
}
}
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@@ -0,0 +1,17 @@
+import scala.concurrent.{duration, future, Await, ExecutionContext}
+import scala.tools.nsc.Settings
+import ExecutionContext.Implicits.global
+
+// Was failing pretty regularly with a ConcurrentModificationException as
+// WrappedProperties#systemProperties iterated directly over the mutable
+// global system properties map.
+object Test {
+ def main(args: Array[String]) {
+ val tries = 1000 // YMMV
+ val compiler = future {
+ for(_ <- 1 to tries) new Settings(_ => {})
+ }
+ for(i <- 1 to tries * 10) System.setProperty(s"foo$i", i.toString)
+ Await.result(compiler, duration.Duration.Inf)
+ }
+}

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