jdk7 b58, VM doesn't smell good

[Rémi Forax]

John Rose a écrit :
> I hope b59 smells better.  I just pushed the changes I've chosen for  
> b59 to the patch repo.
>
> I am working on other changes too, but I am in point-fix mode, as JDK7  
> M3 settles down for JavaOne.
>
> My goal at the moment is to find workarounds for broken stuff, so as  
> not to be making widespread changes.
>
> Here are some workarounds that will help:
>
> --- Use MethodHandles.lookup().findFoo(...) if you run into trouble  
> with cached or public lookup-factories.
>
> Try to access only methods on the current class (the one calling  
> lookup()), or else public methods in public classes.
>
> This avoids bugs with the access checking logic, by exercising the  
> simplest forms of access checking.
>   
Or use reflection (getMethods()), set accessibility 
(setAccessible(true)) and
use MethodHandle.unreflect(java.lang.reflect.Method).

> --- In your method handle invocation sites and in invokedynamic sites,  
> prefer method handles of built-in types.
>
> A symptom of when you might want to do this is "NoClassDefFound" at an  
> invoke site, for an application class that obviously exists.
>
> Generally speaking, the inserted leading argument type to  
> Lookup.findVirtual only gets in the way.  Use convertArguments to  
> change the leading argument to Object, or bind it to an instance  
> immediately.
>   
I've found that if you convert the leading argument of the method handler,
you have to cast the leading argument of MethodHandle.invoke() too.

// in my example
methodHandle = MethodHandles.convertArguments(methodHandle,
            MethodType.make(void.class,
                /*AbstractVisitor.class*/ Object.class,  // workaround 
to NoClassDefFound bug
                Object.class));

// and then
methodHandle.<void>invoke((Object)this, target);
          cast is needed here  ------^

> --- When currying method handles with insertArgument, insert only a  
> leading argument (#0) to a direct method handle.
>
> If you have something more complicated you want to do with currying,  
> consider using a JavaMethodHandle instead.
>
> (Yes, all this should be taken care of for you, and it will be!)
>
> -- John
>   

And it works like a charm :)

Rémi