ClassCastException: cannot assign SerializedLambda to field with ClassLoader
David Holmes
david.holmes at oracle.com
Tue Mar 26 02:34:10 UTC 2019
Hi Seth,
On 26/03/2019 12:16 pm, seth lytle wrote:
> i haven't changed the assignment from the original test case (which was
> accepted as valid at the time). i haven't gone through it in depth, but
> assume that it's ok and used it since people are already familiar with
> it. it appears to me that that example uses reflection to allocate an
> instance using a definitive class loader and then uses a runnable for
> the serialization/deserialization cycle
>
> the class cast exception happens not at the example level, but deep
> inside `readObject` when it's doing an internal assignment
>
> perhaps my choice of words "into a new classloader" was insufficient or
> misleading. in both examples that i've come up with so far, the class
> loader calls defineClass directly without first delegating to super (for
> a subset of the classes). so "into a definitive classloader" might have
> been a better choice
I think the basic problem is that this test loads a nested type into a
different classloader to its enclosing type. I can easily imagine this
messing up the code that gets generated to implement the lambda
expression - but I'd need to examine that code in detail to see exactly
why (others may know this more readily than I do). It's unclear to me
whether this would be considered a bug or a "don't do that" situation.
As of JDK 11, nested types define "nests" at the VM level (see JEP-181)
and it is a requirement that all nest members be defined in the same
package - which implies the same classloader.
David
>
>
>
>
>
> On Mon, Mar 25, 2019 at 9:34 PM David Holmes <david.holmes at oracle.com
> <mailto:david.holmes at oracle.com>> wrote:
>
> Hi Seth,
>
> On 26/03/2019 11:22 am, seth lytle wrote:
> > if a lambda is a field and captures `this`, and it's deserialized
> into a
> > new class loader, it throws a ClassCastException.
>
> Not sure I follow. If you load a class into a different classloader
> then
> you get a different type. It might appear the same to you but it is a
> distinct type, so you can't assign across different instances loaded by
> different classloaders.
>
> Cheers,
> David
> -----
>
> > i came across this bug
> > independently while writing a test, but then found an old openjdk
> bug with
> > a similar issue and tweaked the test case (source below). my version
> > differs only in
> > 1. moved the lambda to a field
> > 2. reference `this` in it
> > 3. uses readAllBytes instead of the internal method
> > 4. formatting
> >
> > running with java 11 or 12 (or java 8 using a substitute for
> readAllBytes)
> > results in:
> > this: test.SerializedLambdaTest$MyCode at 8efb846
> > deSerializedThis: test.SerializedLambdaTest$MyCode at 2b71fc7e
> > runnable:
> >
> test.SerializedLambdaTest$MyCode$$Lambda$1/0x0000000801188440 at 37bba400
> > Exception in thread "main" java.lang.ClassCastException: cannot
> assign
> > instance of java.lang.invoke.SerializedLambda to field
> > test.SerializedLambdaTest$MyCode.runnable2 of type
> > test.SerializedLambdaTest$SerializableRunnable in instance of
> > test.SerializedLambdaTest$MyCode
> > at
> > java.base/java.io
> <http://java.io>.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2190)
> > at
> > java.base/java.io
> <http://java.io>.ObjectStreamClass$FieldReflector.checkObjectFieldValueTypes(ObjectStreamClass.java:2153)
> > at
> > java.base/java.io
> <http://java.io>.ObjectStreamClass.checkObjFieldValueTypes(ObjectStreamClass.java:1407)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.defaultCheckFieldValues(ObjectInputStream.java:2371)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readSerialData(ObjectInputStream.java:2278)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2087)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readArray(ObjectInputStream.java:1993)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readObject0(ObjectInputStream.java:1588)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2355)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readSerialData(ObjectInputStream.java:2249)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2087)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
> > at
> > java.base/java.io
> <http://java.io>.ObjectInputStream.readObject(ObjectInputStream.java:430)
> > at
> >
> test.SerializedLambdaTest$MyCode.deserialize(SerializedLambdaTest.java:35)
> > at test.SerializedLambdaTest$MyCode.run(SerializedLambdaTest.java:51)
> > at test.SerializedLambdaTest.main(SerializedLambdaTest.java:66)
> >
> >
> >
> > https://bugs.openjdk.java.net/browse/JDK-8008770
> >
> >
> > package test;
> >
> > import java.io.ByteArrayInputStream;
> > import java.io.ByteArrayOutputStream;
> > import java.io.IOException;
> > import java.io.InputStream;
> > import java.io.ObjectInputStream;
> > import java.io.ObjectOutputStream;
> > import java.io.Serializable;
> >
> > // from: https://bugs.openjdk.java.net/browse/JDK-8008770
> > public class SerializedLambdaTest {
> > public interface SerializableRunnable extends
> Runnable,Serializable {
> > }
> > public static class MyCode implements SerializableRunnable {
> > SerializableRunnable runnable2 = ()
> > -> {
> > System.out.println("HELLO"+this.getClass());
> > };
> > private byte[] serialize(Object o) {
> > ByteArrayOutputStream baos;
> > try (
> > ObjectOutputStream oos
> > = new ObjectOutputStream(baos = new
> > ByteArrayOutputStream())) {
> > oos.writeObject(o);
> > } catch (IOException e) {
> > throw new RuntimeException(e);
> > }
> > return baos.toByteArray();
> > }
> > private <T> T deserialize(byte[] bytes) {
> > try (
> > ObjectInputStream ois
> > = new ObjectInputStream(new
> > ByteArrayInputStream(bytes))) {
> > return (T) ois.readObject();
> > } catch (IOException|ClassNotFoundException e) {
> > throw new RuntimeException(e);
> > }
> > }
> > @Override
> > public void run() {
> > System.out.println(" this: "+this);
> > SerializableRunnable deSerializedThis
> > = deserialize(serialize(this));
> > System.out.println(" deSerializedThis: "
> > +deSerializedThis);
> >
> > SerializableRunnable runnable = runnable2;
> > System.out.println(" runnable: "+runnable);
> > SerializableRunnable deSerializedRunnable
> > = deserialize(serialize(runnable));
> > System.out.println("deSerializedRunnable: "
> > +deSerializedRunnable);
> > }
> > }
> > public static void main(String[] args) throws Exception {
> > ClassLoader myCl = new MyClassLoader(
> > SerializedLambdaTest.class.getClassLoader()
> > );
> > Class<?> myCodeClass = Class.forName(
> > SerializedLambdaTest.class.getName()+"$MyCode",
> > true,
> > myCl
> > );
> > Runnable myCode = (Runnable) myCodeClass.newInstance();
> > myCode.run();
> > }
> > static class MyClassLoader extends ClassLoader {
> > MyClassLoader(ClassLoader parent) {
> > super(parent);
> > }
> > @Override
> > protected Class<?> loadClass(String name,boolean resolve)
> > throws ClassNotFoundException {
> > if (name.startsWith("test."))
> > synchronized (getClassLoadingLock(name)) {
> > Class<?> c = findLoadedClass(name);
> > if (c==null)
> > c = findClass(name);
> > if (resolve)
> > resolveClass(c);
> > return c;
> > }
> > else
> > return super.loadClass(name,resolve);
> > }
> > @Override
> > protected Class<?> findClass(String name) throws
> > ClassNotFoundException {
> > String path = name.replace('.','/').concat(".class");
> > try ( InputStream is = getResourceAsStream(path)) {
> > if (is!=null) {
> > byte[] bytes = is.readAllBytes();
> > return defineClass(name,bytes,0,bytes.length);
> > } else
> > throw new ClassNotFoundException(name);
> > } catch (IOException e) {
> > throw new ClassNotFoundException(name,e);
> > }
> > }
> > }
> > }
> >
>
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