MethodHandle.asTypeCache can retain classes from unloading

http://mail.openjdk.java.net/pipermail/mlvm-dev/2015-April/006436.html
Peter Levart wrote:

I think there is a Class(Loader) leak in MethodHandle.asType() implementation. If for example some MH (say mhX) is long lived (because it is a system cached MH) and a client "generates" variants from it by invoking mhX.asType(newType) and the newType contains a type (either return type or parameter type) that is loaded by some child ClassLoader, then such derived MH is retained strongly from mhX via the MethodHandle.asTypeCache field. Until this field is overwriten by some other MH, child ClassLoader can not be GCed.

In case this one-element cache is needed to speed things up, it should be a WeakReference, like the following:

http://cr.openjdk.java.net/~plevart/jdk9-dev/MethodHandle.asTypeCacheLeak/webrev.01/