[gambit-list] Speed on XML-parsing

Mikael More mikael.more at gmail.com
Sat Aug 16 10:21:11 EDT 2008


Marc,

just to ensure I got your point. You say that one could create a string-port
more than 20 times faster than Gambit's built-in string ports. I'm
interested in the reason - is this because:

a) If one writes one in scheme code, Gambit may perform function inlining?
b) You presume that the string-port implementation one writes does not need
to be thread-safe, within the context of Gambit's threading system, as is
Gambit's built in string port?

Any more reasons?

Also, what further reasons do you see as to why a SSAX-SXML XML to SXML
deserialization that takes 3 seconds in Java takes 50 seconds in Gambit? I
mean, in general, Gambit code is a lot faster than Java, so this is an
exception to the general rule.

Can you further describe how to create a complete port implementation, such
as a string port or a gzip port?

M

2008/8/16 Marc Feeley <feeley at iro.umontreal.ca>

> If you are really into optimizing the I/O, I suggest you implement
> your own special purpose string-port I/O layer.  Basically you
> redefine read-char to read from a string.  The code below shows that
> this can be over 20 times faster than Gambit's built-in string ports.
> The main reasons for the difference are function inlining and locking
> (to support multithreading).
>
> (define (convoluted-string-length1 str) ;; uses standard string ports
>   (declare (standard-bindings) (fixnum) (not safe))
>   (let ((port (open-input-string str)))
>     (let loop ((i 0))
>       (let ((c (read-char port)))
>         (if (char? c)
>             (loop (+ i 1))
>             i)))))
>
> (define-macro (macro-open-input-string str)
>   `(let ((str ,str))
>      (declare (standard-bindings) (fixnum) (not safe))
>      (cons str 0)))
>
> (define-macro (macro-read-char my-port)
>   `(let ((my-port ,my-port))
>      (declare (standard-bindings) (fixnum) (not safe))
>      (let ((str (car my-port))
>            (pos (cdr my-port)))
>        (if (< pos (string-length str))
>            (let ((c (string-ref str pos)))
>              (set-cdr! my-port (+ 1 pos))
>              c)
>            #!eof))))
>
> (define-macro (open-input-string str) `(macro-open-input-string ,str))
> (define-macro (read-char port) `(macro-read-char ,port))
>
> ;; insert your code after this point, for example:
>
> (define (convoluted-string-length2 str) ;; uses "fast" string ports
>   (declare (standard-bindings) (fixnum) (not safe))
>   (let ((port (open-input-string str)))
>     (let loop ((i 0))
>       (let ((c (read-char port)))
>         (if (char? c)
>             (loop (+ i 1))
>             i)))))
>
> (define (test)
>   (let ((s (make-string 4000000 #\!)))
>     (pretty-print (time (convoluted-string-length1 s)))
>     (pretty-print (time (convoluted-string-length2 s)))))
>
> (test)
>
> ;; (time (convoluted-string-length1 s))
> ;;     704 ms real time
> ;;     703 ms cpu time (661 user, 42 system)
> ;;     1 collection accounting for 50 ms real time (32 user, 19 system)
> ;;     36023288 bytes allocated
> ;;     no minor faults
> ;;     no major faults
> ;; 4000000
> ;; (time (convoluted-string-length2 s))
> ;;     26 ms real time
> ;;     25 ms cpu time (25 user, 0 system)
> ;;     no collections
> ;;     24 bytes allocated
> ;;     no minor faults
> ;;     no major faults
> ;; 4000000
>
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