RFR: 8153334: Replace BufferedInputStreams use of AtomicReferenceFieldUpdater with Unsafe

[Peter Levart]

Hi Paul,

I wanted to try using VarHandles for code internal to JDK but there's a 
problem with MethodHandles.lookup(). It doesn't allow the caller class 
loaded by the bootstrap class loader and located in either java.* or 
sun.* (but not sun.invoke.*) packages:


         private static void checkUnprivilegedlookupClass(Class<?> 
lookupClass, int allowedModes) {
             String name = lookupClass.getName();
             if (name.startsWith("java.lang.invoke."))
                 throw newIllegalArgumentException("illegal lookupClass: 
"+lookupClass);

             // For caller-sensitive MethodHandles.lookup()
             // disallow lookup more restricted packages
             if (allowedModes == ALL_MODES && 
lookupClass.getClassLoader() == null) {
                 if (name.startsWith("java.") ||
                         (name.startsWith("sun.") && 
!name.startsWith("sun.invoke."))) {
                     throw newIllegalArgumentException("illegal 
lookupClass: " + lookupClass);
                 }
             }
         }


...strangely, other bootstrap class loaded callers located in jdk.* are 
allowed. Why such distinction? Is there or will there be an official way 
to use VarHandles in JDK code and not having to resort to work-arounds 
like 
MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP").setAccessible(true)?


Regards, Peter