RFR (XS): 8019184: MethodHandles.catchException() fails when methods have 8 args + varargs

[Christian Thalinger]

On Jul 2, 2013, at 2:04 PM, John Rose <john.r.rose at oracle.com> wrote:

> Good fix, good test.
> 
> Suggestions for the test:
> 
> Change e.printStackTrace() to throw new AssertionError(e), to get earlier detection of config error.

Done.

> 
> Suggest using a more specific type than Exception, maybe even a specific instance (like firstArg), to rule out interference from accidental errors.  Then detect the caught exception in the handler, before returning the desired value.

It seems to be part of the magic that the exception doesn't end up in the handler so I can't check for the exception instance.

> 
> Suggest defining MAX_ARITY (MAX_MH_ARITY?) more categorically as 254, with a comment.  Then have the loop go up to MAX_ARITY-1 with a comment, or put a break at the bottom of the loop body:
>  if (handlerWithArgs.type().parameterCount() == MAX_MH_ARITY)  break;  // no more cases possible

Done.

> 
> As we have seen, arity limits are hard to reason about!
> 
> (Instead of dropArgs you could use something like MethodType.methodType(Object.class, Exception.class, ptypes.toArray()).)

This doesn't work because ptypes.toArray() returns an Object[] and I think that the drop is also part of the magic.  (I have engineered this test after the test case of the bug report.)

Anyway, here is an updated webrev:

http://cr.openjdk.java.net/~twisti/8019184/webrev/

-- Chris

> 
> — John
> 
> On Jul 2, 2013, at 1:33 PM, Christian Thalinger <christian.thalinger at oracle.com> wrote:
> 
>> http://cr.openjdk.java.net/~twisti/8019184/webrev/
>> 
>> 8019184: MethodHandles.catchException() fails when methods have 8 args + varargs
>> Reviewed-by:
>> 
>> The bug seems to be in MethodHandlesImpl.makeGuardWithCatch using ValueConversions.varargsArray:
>> 
>> return makeCollectArguments(ginvoker, ValueConversions.varargsArray(nargs), 0, false);
>> 
>> ValueConversions.varargsArray returns a MethodHandle which's type is:
>> 
>> MethodHandle(Object,Object,Object,Object,Object,Object,Object,Object,Object)Object[]
>> 
>> It doesn't preserve the trailing Object[].
>> 
>> The fix is to call makePairwiseConvert on the result of makeCollectArguments.
>> 
>> src/share/classes/java/lang/invoke/MethodHandleImpl.java
>> test/java/lang/invoke/TestCatchExceptionWithVarargs.java
>> 
>