On 01/04/2018 22:02, Rafael Winterhalter wrote:

1. Java agents cannot define auxiliary classes.

The reason for
using Unsafe is that many instrumentations need to define auxiliary classes
to aid an instrumentation similar to javac which sometimes needs to define
anonymous classes or even synthetic classes. For example, if a Java agent
wants to register an event listener to some framework, such listeners often
declare multiple methods what makes it impossible to fullfil the listener
contract using a lambda expression. Instead, one typically injects an
additional class into the same package as the instrumented class.
This seems a reasonable requirement. As you know, JSR-163 created this API (and JVM TI) for tools to instrument code in mostly benign ways where any additional agent provided helper classes are made visibility via the appendToXXXClassLoaderSearch methods. I don't think the use-case of dynamically generated helper classes came up, I don't recall it coming up on serviceability-dev in the intervening years either. In any case, I think there should be a way to support this scenario, it amounts to a ClassFileTransformer providing the class bytes of additional classes to be defined in the same runtime package as the class being loaded or transformed. There are a number of API choices and it's probably best if we bring proposals to serviceability-dev as that is where this API is maintained.


2. Java proxies cannot invoke default methods of proxied interfaces

The Java proxy API does not currently allow the invocation of an overridden
default method since
the InvocationHandler API only supplies an instance of
The issue of Proxies and default methods has come up on core-libs-dev a few times. In the mean-time, JEP 274 added support for MethodHandles that bind to non-abstract methods in interfaces. I just double checked and I can create a proxy where the invocation handler creates a method handle to the default method, binds it to proxy, and invokes it. I also checked the case where the interface is public in an exported package of a named module. Can you say a bit more, or provide an example, where you run into issues? I'm wondering if you are running into an accessibility issue or something else.


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