ClassCastException: cannot assign SerializedLambda to field with ClassLoader
seth lytle
seth.lytle at gmail.com
Tue Mar 26 15:04:59 UTC 2019
awesome ! thanks for the workaround
peter wrote:
> You can check my claims by changing the type of the field holding the
> lambda to java.lang.Object and see if it works... (It should if my
> memory serves me well :-)
On Tue, Mar 26, 2019 at 3:54 AM Peter Levart <peter.levart at gmail.com> wrote:
> Hi Seth,
>
> I think you stumbled on a "defect" of Java Serialization mechanism.
> Namely, the inability for it to correctly deserialize object graphs
> containing a cycle when an object in such cycle uses the "readResolve()"
> special method to replace the deserialized object with a replacement
> object. SerializedLambda is a class with instances that are 1st
> deserialized from stream then "replaced" with real lambda objects via
> the "readResolve()" method which constructs and returns the "real"
> lambda object. The deserialized SerializedLambda object is nevertheless
> attempted to be (temporarily) assigned to the field that would hold the
> final lambda object, which fails as the filed is of different type than
> SerializedLambda (or supertype).
>
> You can check my claims by changing the type of the field holding the
> lambda to java.lang.Object and see if it works... (It should if my
> memory serves me well :-)
>
> This is a known defect of Java serialization and is not specific to
> serialized lambda.
>
> There were some unsuccessful attempts to fix it during (re)discovery
> when lambdas were being added to Java.
>
> Regards, Peter
>
> On 3/26/19 5:03 AM, seth lytle wrote:
> > 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);
> >>> > > }
> >>> > > }
> >>> > > }
> >>> > > }
> >>> > >
> >>> >
> >>>
>
>
More information about the core-libs-dev
mailing list