[Vm-dev] primFailCode currently dormant?

[Eliot Miranda]

On Mon, May 3, 2010 at 1:58 AM, Igor Stasenko <siguctua at gmail.com> wrote:

>
> On 3 May 2010 03:43, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> >
> >
> >
> > On Sun, May 2, 2010 at 11:47 AM, Igor Stasenko <siguctua at gmail.com>
> wrote:
> >>
> >> On 2 May 2010 21:23, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> >> >
> >> >
> >> >
> >> > On Fri, Apr 30, 2010 at 10:56 PM, Igor Stasenko <siguctua at gmail.com>
> wrote:
> >> >>
> >> >>
> >> >> Hello,
> >> >>
> >> >> Alien adds a new primitive pragma:
> >> >>
> >> >> <primitive: 'foo' error: tempName module: 'bar' >
> >> >>
> >> >> where tempName is auto-declared during parsing as a special temp
> which
> >> >> will be used to retrieve primitive error code. i.e.
> >> >>
> >> >> myMethod
> >> >>  <primitive: 'foo' error: code module: 'bar' >
> >> >> "prim failed , check the error code"
> >> >>  code = 5 ifTrue: [ self error: 'you wrong' ]
> >> >>  code = 666 ifTrue: [ self error: 'you are wrong as hell' ]
> >> >>
> >> >>
> >> >> The problem is, that i found that while its integrated in parser
> >> >> (through Alien package overrides),
> >> >> it leads to nowhere in current Interpreter. :(
> >> >
> >> > But it's fully supported in the Newspeak VM and in the Cog VMs.
>  Please don't delete this.
> >>
> >> i won't. I like being told by prim, _why_ its failed.
> >> I just don't like that this is currently dormant.
> >>
> >> >>
> >> >> The sole reference to primFailCode is only in #primitiveFailFor: ,
> >> >> which actually should be used by prims to set the failure code:
> >> >>
> >> >> Interpreter>>primitiveFailFor: reasonCode
> >> >>        "Set specific primitive failure."
> >> >>        primFailCode := reasonCode.
> >> >>        self primitiveFail.
> >> >>
> >> >>
> >> >> I'd like to propose an alternative implementation:
> >> >>
> >> >> - at VM side , add only a single primitive:
> >> >> primitiveLastFailureCode
> >> >>        self export: true.
> >> >>        self pop: 1 thenPush: (self integerObjectOf: primFailCode).
> >> >>        "reset the code"
> >> >>        primFailCode := 0.
> >> >>
> >> >> At language side, we can support both, old and new format:
> >> >>
> >> >> Add the method , which will retrieve the code:
> >> >>
> >> >> Object>>lastFailureCode
> >> >>  "Primitive: answer the last primitive failure code. Resets the
> failure code.
> >> >>  Note: it can fail only if we're running on older VMs, which has no
> >> >> support of this primitive, if so, answer the generic failure code"
> >> >>  <primitive: 'primitiveLastFailureCode' module: ''>
> >> >>  ^ 0
> >> >>
> >> >>
> >> >>
> >> >> And then, to handle things manually, one could use:
> >> >>
> >> >> Myclass>> foo
> >> >>   <primitive: 'myprimitive' module: 'mymodule>
> >> >>   "we're failed"
> >> >>   | code |
> >> >>   code := self lastFailureCode.
> >> >>   ... handle the error code...
> >> >>
> >> >> And to support the Alien's new pragma pattern
> (primitive:error:module:)
> >> >> it can simply instruct the encoder to generate an implicit bytecode
> >> >> sequence (at method's beginning), which equals to:
> >> >>   temp := self lastFailureCode.
> >> >> (where temp, is one, which used in pragma)
> >> >>
> >> >> What you think?
> >> >
> >> > This is bad for a number of reasons, primarily thread-safety.  There's
> nothing to guarantee that the prim fail code is accessed before a process
> switch which could cause the error code to get overwritten.  Instead if you
> wanted to do something in this area you could get the Newspeak VM and start
> integrating the code there-from.
> >>
> >> Yes. This might be an issue.
> >> I thought, there is no chance interrupting it between
> >> - current prim fail - enter a method - do a #lastFailureCode send
> >>
> >> or it is?
> >> If i remember, an interrupt check performed only on a normal return
> >> from method.
> >
> > Going by the old Teleplace interpreter interrupts are checked on
> activating a method, which includes a failing method.  See senders
> of internalQuickCheckForInterrupts & quickCheckForInterrupts. i.e whenever a
> frame is built for a send. This is indeed between the primitive invocation
> and the send of lastFailureCode.
> >
>
> Aha, so its unsafe. Then, of course, your variant is better.
>
> >>
> >> And a normal return can't happen anywhere between the above stages.
> >>
> >>
> >> I remember your description of setting a temp value with failure code.
> >> Its cool from language side perspective, but ugly & complex at VM side
> >> (i can imagine how ugly and complex that code may look like where have
> >> to crunch a lot of bits and do many various checks before attempting
> >> to store code into temp).
> >
> > Its not at all complicated.  Find the code in the Newspeak VM.  The code
> to load the temp is likely also in the Closure compiler already.  Here's the
> code in internalActivateNewMethod as described on my blog:
>
> Where i can get NewSpeak VM sources?
>

http://newspeaklanguage.org/the-newspeak-programming-language/downloads/ &
on that page newspeak-source-2010-02-23.zip<https://sourceforge.net/projects/newspeakpl/files/newspeak/2010-02-23/newspeak-source-2010-02-23.zip/download>


In there you'll find a
directory newspeak-source-2010-02-23/ns-squeak/squeakpackages/VMMaker/ which
contains all the VMMaker source broken out by class
(e.g. newspeak-source-2010-02-23/ns-squeak/squeakpackages/VMMaker/Interpreter.st)


> >
> >         “Pass primitive error code to last temp if method receives it
> (indicated
> >          by an initial long store temp bytecode). Protect against
> obsolete values
> >          in primFailCode by checking that newMethod actually has a
> primitive.”
> >         primFailCode ~= 0 ifTrue:
> >                  [((self methodHeaderHasPrimitive: methodHeader)
> >                   and: [(self byteAtPointer: localIP + 1) = 129 "long
> store temp"]) ifTrue:
> >
>         [errorCode := self getErrorObjectFromPrimFailCode.
> >                            self longAt: localSP put: errorCode "nil if
> primFailCode == 1, or primFailCode"].
> >                  primFailCode := 0].
> >>
> >> > But I'm now in a position to put some effort into open sourcing Cog,
> having completed my current Teleplace assignment, and so perhaps being
> patient and waiting a little longer is the best approach.  In the mean time
> please don't change any of the primitive fail code stuff.  Its fully
> functional in the code we're using at Teleplace and in Newspeak and it would
> be good to avoid incompatibilities.
> >>
> >> well, my proposal actually don't requires altering existing code.
> >> It just adds a prim, which exposing the failure code value to language
> side.
> >
> > Alas in a way that can't provide reliable access given the VM's current
> interrupt response.  I don't mean to frustrate you, but I do hope to get my
> code out soon.
>
> I see not reason , why i should be frustrated :)
> You shown me that my approach is unreliable. So, even if its simpler,
> it can't be used.
>
> And there is a NewSpeak code, which waits to be integrated. So, its a
> work to do, not to get frustrated :)
>

Good :)

best,
Eliot


>
>
> > best
> > Eliot
> >
> >>
>
>
> --
> Best regards,
> Igor Stasenko AKA sig.
>
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