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scalasbtclassloader

sbt using multiple classloaders

Sbt seems to be using different classloaders, making some tests failing when run more than once in an sbt session, with the following error:

[info]   java.lang.ClassCastException: net.i2p.crypto.eddsa.EdDSAPublicKey cannot be cast to net.i2p.crypto.eddsa.EdDSAPublicKey
[info]   at com.advancedtelematic.libtuf.crypt.EdcKeyPair$.generate(RsaKeyPair.scala:120)

I tried equivalent code using pattern matching instead of asInstanceOf and I get the same result.

How can I make sure sbt uses the same class loader for all test executions in the same session?

Solution

  • I think it's related to this: Do security providers cause ClassLoader leaks in Java?. Basically Security is re-using providers from old class-loaders. So this could happen in any multi-classpath environment (like OSGi), not just SBT.

    Fix for your build.sbt (without forking): 

    testOptions in Test += Tests.Cleanup(() => 
  java.security.Security.removeProvider("BC"))

    Experiment:

    sbt-classloader-issue$ sbt
> test
[success] Total time: 1 s, completed Jul 6, 2017 11:43:53 PM
> test
[success] Total time: 0 s, completed Jul 6, 2017 11:43:55 PM

    Explanation:

    As I can see from your code (published here):

    Security.addProvider(new BouncyCastleProvider)

    you're reusing the same BouncyCastleProvider provider every-time you run a test, as your Security.addProvider works only first time. As sbt creates new class-loader for every "test" run, but re-uses the same JVM - Security is kind-of JVM-scoped singleton as it was loaded by JVM-bootstrap, so classOf[java.security.Security].getClassLoader() == null and sbt cannot reload/reinitialize this class.

    And you can easily check that 

    classOf[org.bouncycastle.jce.spec.ECParameterSpec].getClassLoader()
res30: ClassLoader = URLClassLoader with NativeCopyLoader with RawResources

    org.bouncycastle classes are loaded with custom classloader (from sbt) which changes every-time you run test.

    So this code:

    val generator = KeyPairGenerator.getInstance("ECDSA", "BC")

    gets instance of class loaded from old classloader (the one used for first "test" run) and you're trying to initialize it with spec from new classloader:

    generator.initialize(ecSpec)

    That's why you're getting "parameter object not a ECParameterSpec" exception. The reasoning around "net.i2p.crypto.eddsa.EdDSAPublicKey cannot be cast to net.i2p.crypto.eddsa.EdDSAPublicKey" is basically same.