[9] RFR (S): 8036117: MethodHandles.catchException doesn't handle VarargsCollector right (8034120 failed)

[Vladimir Ivanov]

Chris, thanks for the review.

John suggested an elegant way to fix the problem - use asFixedArity.

Updated fix:
http://cr.openjdk.java.net/~vlivanov/8036117/webrev.01/

Best regards,
Vladimir Ivanov

On 3/8/14 4:51 AM, Christian Thalinger wrote:
> Seems good to me.  I’d like to have another name for this method:
>
> +     private static Object invokeCustom(MethodHandle target, Object... args) throws Throwable {
>
> On Mar 4, 2014, at 12:00 PM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
>
>> http://cr.openjdk.java.net/~vlivanov/8036117/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8036117
>> 84 lines changed: 74 ins; 3 del; 7 mod
>>
>> I have to revert a cleanup I did for 8027827.
>> MethodHandle.invokeWithArguments (and generic invocation) has unpleasant
>> peculiarity in behavior when used with VarargsCollector. So,
>> unfortunately, invokeWithArguments is not an option there.
>>
>> Looking at the API (excerpts from javadoc [1] [2]), the following
>> condition doesn't hold in that case:
>>    "trailing parameter type of the caller is a reference type identical
>> to or assignable to the trailing parameter type of the adapter".
>>
>> Example:
>>    target.invokeWithArguments((Object[])args)
>>    =>
>>    target.invoke((Object)o1,(Object)o2,(Object)o3)
>>    =/>
>>    target.invokeExact((Object)o1, (Object)o2, (Object[])o3)
>>
>> because Object !<: Object[].
>>
>> The fix is to skip unnecessary conversion when invoking a method handle
>> and just do a pairwise type conversion.
>>
>> Testing: failing test case, nashorn w/ experimental features (octane)
>>
>> Thanks!
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> [1] MethodHandle.invokeWithArguments
>> "Performs a variable arity invocation, ..., as if via an inexact invoke
>> from a call site which mentions only the type Object, and whose arity is
>> the length of the argument array."
>>
>> [2] MethodHandle.asVarargsCollector
>> "When called with plain, inexact invoke, if the caller type is the same
>> as the adapter, the adapter invokes the target as with invokeExact.
>> (This is the normal behavior for invoke when types match.)
>>
>> Otherwise, if the caller and adapter arity are the same, and the
>> trailing parameter type of the caller is a reference type identical to
>> or assignable to the trailing parameter type of the adapter, the
>> arguments and return values are converted pairwise, as if by asType on a
>> fixed arity method handle.
>>
>> Otherwise, the arities differ, or the adapter's trailing parameter type
>> is not assignable from the corresponding caller type. In this case, the
>> adapter replaces all trailing arguments from the original trailing
>> argument position onward, by a new array of type arrayType, whose
>> elements comprise (in order) the replaced arguments."
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>
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