1 Sep 2009 14:16
OUTPUT-REPLACEMENT restart for fd-streams external-format
Christophe Rhodes <csr21 <at> cantab.net>
2009-09-01 12:16:32 GMT
2009-09-01 12:16:32 GMT
Hi, I'm nervous of some work that I'm doing, and I'd quite like a sanity-check before I continue too far, because it involves fd-streams (and I know that several people have thrown their hands up in horror at the fd-streams "logic"). The two attached patches implement proper error checking for the utf-8 format (so that surrogate codepoints aren't sent through, for example), and an OUTPUT-REPLACEMENT restart to allow the program to send something different in the event of an encoding error.
This interactive functionality, while nice (if it works) isn't the actual objective; what I actually need is "liberal" or possibly "interchange" versions of external formats, so that we don't have the disastrous situation of trying to tell the user (via the debugger) that some character in a string isn't encodable in the external format that the debugger is using. If I can get that functionality with the generality of the restart approach, though, I'll go for it (even if that functionality ends up not being used). Anyway, the actual questions: firstly, does anything look directly wrong or problematic with the above patches; secondly, I'm also attaching a test file; can people suggest any other tests that I should be doing?(Continue reading)
> + Your slot-xyz-using-class methods specalize not only on the
> metaclass and the slot definition class, but also on the object.
> That's redundant, it doesn't buy you anything, since you want
> instances of the metaclass to inherit from the object class anyway.
> Leaving out the specialize may allow SBCL to use faster caches.
That makes sense, I'll do that.
[...]
>> Unfortunately as all mmap slots are always boundp, we have to munge
>> the general initialize-instance to set default slot values. This is
>> quite unfortunate. Is there a more sensible way of doing this (along
>> the lines of the way structure slots are handled)?
>
> What do you mean by 'munge' (sorry, I'm not a native speaker)?
I mean that the way I do it is not at all nice and pretty. I think it is
probably clearer to show the code
(defmethod initialize-instance :before ((instance mm-object) &rest initargs)
(declare (optimize speed) (dynamic-extent initargs))
(cond ((eq '%ptr (first initargs)) ;;; XXX this is for speed; if %ptr is given it must be first
(setf (%ptr instance)
(second initargs)))
(t
(let ((class (class-of instance)))
(setf (%ptr instance) (mm-metaclass-alloc class))
;;; XXX this is a horrible hack because we don't support unbound slots
;;; not in shared-initialize because that is more likely to destroy the system's optimizations????
(let ((slot-definitions (class-slots class)))
(loop for s in slot-definitions do
(when (and (slot-definition-memory-mapped s)
(slot-definition-initfunction s))
(unless (get-properties initargs (slot-definition-initargs s))
(setf (slot-value-using-class class instance s)
(funcall (slot-definition-initfunction s))))))))))
instance)
> Note that you can also define methods on make-instance and allocate-
> instance, if that helps.
The situation when most instance creation occurs is when an object is
instantiated from the database into a Lisp object (generally with one
slot, (hopefully) a fixnum "mptr").
It is possible for the object to have normal instance slots (caches or
temporary slots). Those should be initialized according to the normal
rules. It would be possible to generate an compiled function to do this
explicitly for all such slots -- firstly calling allocate-instance(?)
directly and then the init-functions for each slot.
One approach I was considering was to inherit from structure-class
instead of standard-class, etc. This would finesse the initialisation as
structure slots are also never unbound. But I think that is not really
portable? (And perhaps not sensible)
[...]
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. 
RSS Feed