[Vm-dev] [Pharo-project] is there a way to avoid all the #tryNamedPrimitive:with: * in ProtoObject

[Mariano Martinez Peck]

On Thu, Jan 26, 2012 at 11:38 AM, Igor Stasenko <siguctua at gmail.com> wrote:

>
> On 26 January 2012 11:25, stephane ducasse <stephane.ducasse at gmail.com>
> wrote:
> >
> >> phew... done reading through overquoting :)
> >>
> >> +1000 to removing tryXYZprimitive:
> >>
> >> I was always wondering what those methods for, until i met a need to
> >> support debugging when invoking nativeboost-prim methods,
> >> because it needs special handing when invoking methods with native
> >> code via debugger.
> >>
> >> Then i understood that this mechanism is necessary.. yet a bit awkward..
> >>
> >> Funny. Even after implementing the fix, I still do not understand why
> all these is needed. Can someone explain to a newbie why invoking
> primitives (whether they are normal primitives, named primitives or NB
> primitives) from the debugger is different than invoking them normally (as
> when they are invoked by normal code)
> >
> > Yes I want to understand too.
> >
>
> Here the hint for you:
>  - what should happen when you doing 'step in' on method, which has a
> primitive?
>
> Apparently, it should invoke that primitive , otherwise you will have
> difference between running and debugging modes,
> and will have different results, which makes debugger useless.
> So debugger should detect "somehow" if primitive was failed, and then
> step in into given method,
> or if its not, then step in = step over.
>
> And these 'tryXYZ ... ' is exactly for solving this dilemma.
>

Thanks Igor. So I wrote what I understood. Problem is that I always write
for newbies (like me) so if it is too obvios or too long to put it as
comment, let me know.
I would appreaciate if someone can validate what I wrote.
Today I will create a slice with mentioned solution + comments + removal of
all those tryNamedPrimitive*.

----

"When using the debugger we want to run a method step by step. But what
happens when we do a step into a CompiledMethod which has a primitive? If
such a method is executed form outside the Debugger (normal scenario)
the VMknows that such
CompiledMethod has a primitive declaration and hence executes it. If it
fails, then it continues executing all the bytecodes of the method.
Otherwise, it just returns.

Now, what is the problem with the Debugger? The problem is that if the
primitive fail, we don't want that the VM directly executes all the
remaining bytecodes of the method. Instead, we would like to go step by
step with he Debugger, just as happens with normal methods.

To solve the mentioned problem, we use the following trick: We have the
original compiled method (the one that has a primitive invocation), the
receiver and the arguments. So the idea is to use a template compiled
method that ONLY contains the primitive declaration (it doesn't include all
the original smalltalk code after the primitive). #
tryNamedPrimitiveTemplateMethod answers such a template method which looks
like:

tryNamedPrimitive
    <primitive:'to be set later' module:'to be ser later'>
    ^ ContextPart primitiveFailToken'

 Since this method does not change its bytecodes for every invocation, we
can reuse it for all methods with primitives. There are only 2 things we
have to change in the template: the number of arguments and the primitive
declaration (to use the correct primitive name and module name).

Then what we do is to run that compiled method with the receiver and
arguments we have. The result is that we will be invoking almost the same
original method but a slightly different version that does not have the
smalltalk part after the primitive and that in contrast is sends #
primitiveFailToken (which tells the Debugger what to do after). If this
method invocation does not fail, then the Debugger continues debugging the
sender of the primitive method. In this case, the step in is the same as
step over. If the primitive fails, then the debugger continues executing
the smalltalk part after the primitive method. In this case, step in is a
real step in.  "







>
> --
> Best regards,
> Igor Stasenko.
>



-- 
Mariano
http://marianopeck.wordpress.com
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