Proposed API for JEP 259: Stack-Walking API

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Mandy Chung" <mandy.chung at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: core-libs-dev at openjdk.java.net
> Envoyé: Samedi 31 Octobre 2015 23:59:01
> Objet: Re: Proposed API for JEP 259: Stack-Walking API
> 
> 
> > On Oct 31, 2015, at 11:29 AM, Remi Forax <forax at univ-mlv.fr> wrote:
> > 
> > Hi Mandy,
> > I've crawled the code and the documentation again.
> > 
> > In the doc and in the code, a lambda with one parameter doesn't require
> > parenthesis around the parameter,
> >  (s) -> s.doSomething()
> > should be
> >  s -> s.doSomething().
> > 
> 
> Oh right.  (It didn’t look right to me but didn’t pay attention to it).
> 
> > 
> > In the doc of StackWalker,
> > in the first example, the local variable 'frame' should be named
> > ‘callerClass'
> > 
> 
> Fixed
> > 
> > In the doc of getCallerClass(),
> > the first example do a skip(2) which i believe is not necessary anymore,
> 
> It has to skip two frames.  Use the second example, the stack looks like
> this:
> 
> StackWalk::getCallerClass
> Util::getResourceBundle
> Foo::init
> :
> :

Ok, get it !

> 
> > also instead of Optional.orElse, orElseGet is better because it avoids to
> > evaluate
> > Thread.currentThread().getClass() if not necessary.
> > 
> > So the example should be:
> >   walk(s -> s.map(StackFrame::getDeclaringClass)
> >              .findFirst()).orElseGet(() ->
> >              Thread.currentThread().getClass());
> > 
> 
> This would return Util.class instead of Foo.class
> 
> > In the second example, the field walker should be declared 'final’.
> 
> Sure. Fixed.
> 
> > 
> > And as i said earlier, the signature of walk() is:
> >  <T> T walk(Function<? super Stream<StackWalker.StackFrame>, ? extends T>
> >  function, IntUnaryOperator batchSizeMapper)
> > 
> 
> I was pondering it and that’s why not changed in the last update.  I agree
> with the upper bounded wildcard "? extends T” for the return type of the
> function.
> 
> But for the function’s input argument, can you help me understand why it
> should take "? super Stream<StackWalker.StackFrame>”?  Is it useful to have
> function accepting supertype of Stream<StackFrame> rather than
> Stream<StackFrame>?  VM should be the only source producing this StackFrame
> stream.

currently this code doesn't compile, and should IMO,
  Function<BaseStream<StackWalker.StackFrame>, Void> fun = null;
  stackWalker.walk(fun);

> 
> On the other hand, I wonder if the stream argument should be Stream<? extends
> StackFrame> that may allow future implementation change.
> 
> <T> T walk(Function<Stream<? extends StackWalker.StackFrame>, ? extends T>
> function, …)

A stream of ? extends StackFrame means that you can not call any methods of Stream<T> that takes a T as parameter because the compiler can not enforce that the type is correct, so you can not call neither reduce(BinaryOperator<T> 
) nor reduce(T, BinaryOperator<T>).

If you want to be able to send subtypes of StackFrame and know that at compile time, it's better to parameterized the StackWalker class by the type of StackFrame.  


> 
> Mandy

Rémi