Review Request JDK-8186050: StackFrame should provide the method signature

[mandy chung]

On 8/28/17 4:23 PM, Paul Sandoz wrote:
> Hi Mandy,
>
> MethodType::fromMethodDescriptorString​ (and the three arg Class.forName) requires that a class loader be supplied. Perhaps for the thing consuming StackWalker it’s not possible to reproduce a MethodType (or components of) from the descriptor string
The class loader can be obtained from 
StackFrame::getDeclaringClass().getClassLoader().
>   much like it may not possible to reproduce the declaring class from the class name string, hence the need for RETAIN_CLASS_REFERENCE?

Right and also security permission check can be performed once when 
getting StackWalker instance.  No security permission check is performed 
for each StackFrame::getDeclaringClass for better performance.
> If i understand you correctly i think you are saying the method descriptor is more useful for informational (logging say) purposes?

Yes for completeness since the method signature is currently unavailable.

Mandy
>
> Paul.
>
>> On 28 Aug 2017, at 15:57, mandy chung <mandy.chung at oracle.com> wrote:
>>
>> Method signature is missing in the StackFrame API. This proposes to add StackFrame::getMethodDescriptor method to return the method descriptor in a stack frame.
>>
>> Webrev at:
>> http://cr.openjdk.java.net/~mchung/jdk10/webrevs/8186050/webrev.00/index.html
>>
>> There are a couple options how to present the method signature in the API level:
>> 1. Class<?>[] getParameterTypes() and Class<?> getReturnTypes() similiar to what java.lang.reflect.Method has.
>> 2. java.lang.invoke.MethodType
>> 3. a String representation (i) comma-separated list of the method's formal parameter types (ii) bytecode method descriptor as specified in JVMS
>>
>> Returning Class<?> instance should require to add a new StackWalker option to access to the parameter types and return type for option #1 and #2. StackFrame::getDeclaringClass requires the stack walker to have the RETAIN_CLASS_REFERENCE capability.
>>
>> Option #2 returning MethodType is handy while java.lang would reference a type in java.lang.invoke.
>>
>> Option #3 requires the caller to parse the return string and call Class.forName to get the Class<?> instance. OTOH MethodType::fromMethodDescriptorString​ method that returns MethodType from a bytecode method descriptor string.
>>
>> Method signature is for information for typical cases. Getting Class<?> for the parameter types and return type would be a niche case. I think returning the method descriptor string is a good option - keep the API simple and can use MethodType::fromMethodDescriptorString​ to get back the types if needed.
>>
>> thanks
>> Mandy