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

Tue Mar 11 16:09:33 UTC 2014

On 03/11/2014 03:05 PM, Vladimir Ivanov wrote:
>>> You raised totally valid question.
>>>
>>> I marked MethodHandleImpl.prepend with @Hidden annotation because it
>>> is internal implementation detail of JSR292.
>>>
>>> You are right that normally a callee can't see it on stack. *But it's
>>> possible to observe it when stack trace is queried from a separate
>>> thread. *
>>
>> Is this good or bad? It enables tools to see it (for example sampling
>> profilers, etc...).
> For the purposes of sampling profilers (and other monitoring tools) 
> @Hidden should be completely ignored.  These tools should use 
> appropriate API to get the data.
>
> I looked into the code and @Hidden has even less effect than I thought 
> initially. It affects very limited set of cases - only users of 
> JVM_FillInStackTrace (when filling exception's stack trace, 
> Thread.dumpStack()). Calls to Thread.getStackTrace() from a separate 
> thread omit stack trace filtering.

So all you're achieving by annotating prepend() method is that any 
exception stack trace, in case it is thrown inside the prepend() method, 
will hide where it was thrown from. In case all LambdaForm frames 
leading to the prepend() method were also hidden, the exception would 
appear to be thrown from the invocation of the MH...

Regards, Peter

>
> Best regards,
> Vladimir Ivanov
>
>> Regards, Peter
>>
>>>
>>> There's not much value in it in this particular case, but I decided to
>>> reduce possible noise.
>>>
>>> Best regards,
>>> Vladimir Ivanov
>>>
>>> On 3/11/14 3:35 PM, Peter Levart wrote:
>>>> Hi,
>>>>
>>>> Excuse my ignorant question: What is the purpose of @LambdaForm.Hidden
>>>> annotation?
>>>>
>>>> I suspect it has to do with hiding the call frames in stack traces 
>>>> that
>>>> are part of LambdaForm invocation chain. In this case, method:
>>>>
>>>>      private static Object[] prepend(Object elem, Object[] array)
>>>>
>>>> in MethodHandleImpl need not be annotated with this annotation, since
>>>> it's call frame is not on stack when one of the target methods is
>>>> executed. It's just a function used to calculate the argument of the
>>>> call. In fact, if prepend() ever throws exception (NPE in case 
>>>> array is
>>>> null?), It would be preferable that it's call frame is visible in the
>>>> stack trace.
>>>>
>>>> Am I right or am I just talking nonsense?
>>>>
>>>> Regards, Peter
>>>>
>>>>
>>>> On 03/11/2014 12:12 AM, Vladimir Ivanov wrote:
>>>>> John, Chris, thanks!
>>>>>
>>>>> Best regards,
>>>>> Vladimir Ivanov
>>>>>
>>>>> On 3/11/14 3:08 AM, Christian Thalinger wrote:
>>>>>> Even better.
>>>>>>
>>>>>> On Mar 10, 2014, at 3:21 PM, Vladimir Ivanov
>>>>>> <vladimir.x.ivanov at oracle.com> wrote:
>>>>>>
>>>>>>> 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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