On Oct 13, 2007, at 2:52 PM, tim Rowledge wrote:

>
> On 13-Oct-07, at 2:02 PM, Robert Withers wrote:
>
>> Ok, this gets me into the CompiledMethod, with which I have very  
>> little experience.  I did find that the 'source' toggle button in  
>> a browser has a bytecodes option.  It didn't help me much, seeing  
>> the bytecodes.  I am trying to find a way to invoke a bytecode  
>> primitive from the image.
>
> Why?

I will do my best to answer this seemingly innocuous, simple  
question.  The short answer is that I am reviving my efforts at  
incorporating eventual references, a la SqueakElib, in the Squeak  
image.   This entails making the VM eventual safe.

The longer answer forgets all of the networking work I did, which I  
managed to leverage into SSL and SSH.  I want to allow some object  
references to be eventual and thereby defer method evaluation to some  
future time after invocation.  This works ok for receivers that are  
eventual (4 eventual + 5) -> promise that later evaluates #+ and  
resolves to eventual(9).  In this case, I intercept the msg send and  
send it eventually.

The problem I perceive I have is when we have (4 + 5 eventual).   
There is nothing that intercepts it.  We can't have eventual  
references which are used as arguments to indexed or named  
primitives.   I am trying to fix this.  It's fuzzy, but there are  
several issues I am working through here, which I have just now named  
the intercept problem, the invocation problem, the inoculation problem.

The intercept problem: modify all bytecode/primitive functions to  
check arguments on the stack for eventual references (ugh), if  
eventual arg exists, contaminate the receiver as an eventual ref  
(#becomeForward:), package the args and the primitiveIndex (call it  
an EventualPrimitiveInvocation) and eventally send to an eventual  
join of all eventual args + receiver.  It runs when all eventual refs  
are resolved.  It gets fuzzy here, but the eventual contagion will  
spread to all objects using an eventual ref to maintain message  
order.  Return a promise ref on the stack for the eventual result of  
this future computation.

The invocation problem: the issue I am exploring in this email.  I  
need to unwrap local eventual refs (not remote eventual refs or  
promises) to use as arguments.  I need to invoke the bytecode/ 
primitive prim where interception occurred.  I need to resolve the  
promise created from the intercept.

The inoculation problem: when the system has finished eventual  
sending to system contaminated eventual ref, then inoculate the ref  
back to a non-eventual reference.

I hope this makes some sense.

>
>> So, for instance, given 2 SmallIntegers in hand, I want to run  
>> bytecodePrimAdd without running #+.
>
> Err, given a bytecode named 'bytecodePrimAdd' what would you expect  
> it to do? Why, it runs the same code that primitiveAdd does, modulo  
> the bytecode version knowing that it will be inlined into the big  
> bytecode loop. And oddly enough, that very fact means that if you  
> *did* manage to invoke it by some devious magic, it would cause  
> some interesting issue because you'd be affecting the in-loop  
> values of stack pointer etc, which could cause all sorts of fun.

Ok, I am confused as to which gets called.  #primitiveAdd is in the  
primitive table as number 1, so I guess that shows up in the mcache  
for primitiveIndex 1, and thus gets invoked.   Is it right?  I would  
be happy to run #primitiveAdd, but wouldn't it also have fun with  
affecting values of the stack pointer and such?

>
>> Is there a way to do this?  I am digging through  
>> #lookupInMethodCacheSel:class: at the moment to see how primitive  
>> dispatch works.
> Why? What on earth are you doing? Message sending is designed to be  
> atomic and trying to insert yourself in the middle is likely to go  
> boom. You really are in danger of branching to the Halt and Catch  
> Fire instruction...

I think I need a primitive of my own to marshall the stack args, so  
method lookup and activate the primitive.  On eventual ref  
resolution, I can call a method with this primitiveIndex, where the  
receiver is the EventualPrimitiveInvocation obj.

thanks,
Rob

>
> tim
> --
> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> I came, I saw, I deleted all your files.
>
>
>