rednaxelafx commented on a change in pull request #28463:
URL: https://github.com/apache/spark/pull/28463#discussion_r420784636
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File path: core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala
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@@ -414,6 +433,142 @@ private[spark] object ClosureCleaner extends Logging {
}
}
+private[spark] object IndylambdaScalaClosures extends Logging {
+ // internal name of java.lang.invoke.LambdaMetafactory
+ val LambdaMetafactoryClassName = "java/lang/invoke/LambdaMetafactory"
+ // the method that Scala indylambda use for bootstrap method
+ val LambdaMetafactoryMethodName = "altMetafactory"
+ val LambdaMetafactoryMethodDesc = "(Ljava/lang/invoke/MethodHandles$Lookup;"
+
+ "Ljava/lang/String;Ljava/lang/invoke/MethodType;[Ljava/lang/Object;)" +
+ "Ljava/lang/invoke/CallSite;"
+
+ /**
+ * Check if the given reference is a indylambda style Scala closure.
+ * If so, return a non-empty serialization proxy (SerializedLambda) of the
closure;
+ * otherwise return None.
+ *
+ * @param maybeClosure the closure to check.
+ */
+ def getSerializationProxy(maybeClosure: AnyRef): Option[SerializedLambda] = {
+ val maybeClosureClass = maybeClosure.getClass
+
+ // shortcut the fast check:
+ // indylambda closure classes are generated by Java's LambdaMetafactory,
and they're always
+ // synthetic.
+ if (!maybeClosureClass.isSynthetic) return None
+
+ val implementedInterfaces =
ClassUtils.getAllInterfaces(maybeClosureClass).asScala
+ val isClosureCandidate = implementedInterfaces.exists(_.getName ==
"scala.Serializable") &&
+ implementedInterfaces.exists(_.getName.startsWith("scala.Function"))
+
+ if (isClosureCandidate) {
+ try {
+ val lambdaProxy = inspect(maybeClosure)
+ if (isIndylambdaScalaClosure(lambdaProxy)) Option(lambdaProxy)
+ else None
+ } catch {
+ case e: Exception =>
+ // no need to check if debug is enabled here the Spark logging api
covers this.
+ logDebug("The given reference is not an indylambda Scala closure.",
e)
+ None
+ }
+ } else {
+ None
+ }
+ }
+
+ def isIndylambdaScalaClosure(lambdaProxy: SerializedLambda): Boolean = {
+ lambdaProxy.getImplMethodKind == MethodHandleInfo.REF_invokeStatic &&
+ lambdaProxy.getImplMethodName.contains("$anonfun$")
+ // && implements a scala.runtime.java8 functional interface
+ }
+
+ def inspect(closure: AnyRef): SerializedLambda = {
+ val writeReplace = closure.getClass.getDeclaredMethod("writeReplace")
Review comment:
Not a copy, but a "serialization proxy" object that holds on to the
symbolic information of the original closure object.
The original closure object contains too much runtime-specific information
(e.g. class loader info, reference to runtime-generated lambda class) that's
not suitable for serialization. So the JDK uses a "serialization proxy" that
only holds on to the symbolic info for serialization purposes.
Spark's `ClosureCleaner` abuses this serialization proxy for introspection
into what's inside the black box.
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