pack-priv Interface BootstrapCallInfo<T>

API Note

The lookup object is not included in this bundle of information, so as not to obscure the access control logic of the program. In cases where there are many thousands of parameters, it may be preferable to pull their resolved values, either singly or in batches, rather than wait until all of them have been resolved before a constant or call site can be used.

A push mode bootstrap method can be adapted to a pull mode bootstrap method, and vice versa. For example, this generic adapter pops a push-mode bootstrap method from the beginning of the static argument list, eagerly resolves all the remaining static arguments, and invokes the popped method in push mode. The callee has no way of telling that it was not called directly from the JVM.

static Object genericBSM(Lookup lookup, BootstrapCallInfo<Object> bsci)
    throws Throwable {
  ArrayList<Object> args = new ArrayList<>();
  args.add(lookup);
  args.add(bsci.invocationName());
  args.add(bsci.invocationType());
  MethodHandle bsm = (MethodHandle) bsci.get(0);
  List<Object> restOfArgs = bsci.asList().subList(1, bsci.size();
  // the next line eagerly resolves all remaining static arguments:
  args.addAll(restOfArgs);
  return bsm.invokeWithArguments(args);
}
 

In the other direction, here is a combinator which pops a pull-mode bootstrap method from the beginning of a list of static argument values (already resolved), reformats all of the arguments into a pair of a lookup and a BootstrapCallInfo, and invokes the popped method. Again the callee has no way of telling it was not called directly by the JVM, except that all of the constant values will appear as resolved. Put another way, if any constant fails to resolve, the callee will not be able to catch the resulting error, since the error will be thrown by the JVM before the bootstrap method is entered.

static Object genericBSM(Lookup lookup, String name, Object type,
                         MethodHandle bsm, Object... args)
    throws Throwable {
  ConstantGroup cons = ConstantGroup.makeConstantGroup(Arrays.asList(args));
  BootstrapCallInfo<Object> bsci = makeBootstrapCallInfo(bsm, name, type, cons);
  return bsm.invoke(lookup, bsci);
}