ClassCastException: cannot assign SerializedLambda to field with ClassLoader
seth lytle
seth.lytle at gmail.com
Tue Mar 26 04:03:41 UTC 2019
it's a nested class, but it's loaded with the same class loader as the
toplevel.
which is what i thought you thought was the problem when
you wrote:
> this test loads a nested type into a different classloader to its
enclosing type
and:
> it is a requirement that all nest members be defined in the same
> package - which implies the same classloader
On Mon, Mar 25, 2019 at 11:40 PM David Holmes <david.holmes at oracle.com>
wrote:
> On 26/03/2019 1:06 pm, seth lytle wrote:
> > i still get the same stack trace after breaking the example out into two
> > files. does that sufficiently address the nesting issue ?
>
> ??
>
> public static class MyCode ...
>
> is still a nested class.
>
> David
>
> > file: SerializedLambdaTest
> > package test;
> >
> > import java.io.ByteArrayInputStream;
> > import java.io.ByteArrayOutputStream;
> > import java.io.IOException;
> > import java.io.ObjectInputStream;
> > import java.io.ObjectOutputStream;
> > import java.io.Serializable;
> >
> > // from: https://bugs.openjdk.java.net/browse/JDK-8008770
> > public class SerializedLambdaTest implements Runnable {
> > public void run() { new MyCode().run(); }
> > 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);
> > }
> > }
> > }
> >
> >
> > file: MyClassLoader
> > package test;
> >
> > import java.io.IOException;
> > import java.io.InputStream;
> >
> > 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 (final 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);
> > }
> > }
> > public static void main(String[] args) throws Exception {
> > ClassLoader myCl = new MyClassLoader(
> > MyClassLoader.class.getClassLoader()
> > );
> > Class<?> myCodeClass = Class.forName(
> > "test.SerializedLambdaTest",
> > true,
> > myCl
> > );
> > Runnable myCode = (Runnable) myCodeClass.newInstance();
> > myCode.run();
> > }
> > }
> >
> >
> >
> >
> > On Mon, Mar 25, 2019 at 10:34 PM David Holmes <david.holmes at oracle.com
> > <mailto:david.holmes at oracle.com>> wrote:
> >
> > 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>
> > > <mailto: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>
> > >
> > <http://java.io
> >.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2190)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectStreamClass$FieldReflector.checkObjectFieldValueTypes(ObjectStreamClass.java:2153)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectStreamClass.checkObjFieldValueTypes(ObjectStreamClass.java:1407)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.defaultCheckFieldValues(ObjectInputStream.java:2371)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readSerialData(ObjectInputStream.java:2278)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2087)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readArray(ObjectInputStream.java:1993)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readObject0(ObjectInputStream.java:1588)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2355)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readSerialData(ObjectInputStream.java:2249)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2087)
> > > > at
> > > > java.base/java.io <http://java.io>
> > >
> > <http://java.io
> >.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
> > > > at
> > > > java.base/java.io <http://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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