Re: RPC performance

[ludovic.courtes@inria.fr (Ludovic Courtès)]

Heya,

Andy Wingo <wingo@igalia.com> skribis:

> On Mon 19 Jun 2017 10:15, ludovic.courtes@inria.fr (Ludovic Courtès) writes:
>
>> +(define (buffering-output-port port buffer)
>> +  ;; Note: In Guile 2.2.2, custom binary output ports already have their own
>> +  ;; 4K internal buffer.
>> +  (define size
>> +    (bytevector-length buffer))
>> +
>> +  (define total 0)
>> +
>> +  (define (flush)
>> +    (put-bytevector port buffer 0 total)
>> +    (set! total 0))
>> +
>> +  (define (write bv offset count)
>> +    (if (zero? count)                             ;end of file
>> +        (flush)
>> +        (let loop ((offset offset)
>> +                   (count count)
>> +                   (written 0))
>> +          (cond ((= total size)
>> +                 (flush)
>> +                 (loop offset count written))
>> +                ((zero? count)
>> +                 written)
>> +                (else
>> +                 (let ((to-copy (min count (- size total))))
>> +                   (bytevector-copy! bv offset buffer total to-copy)
>> +                   (set! total (+ total to-copy))
>> +                   (loop (+ offset to-copy) (- count to-copy)
>> +                         (+ written to-copy))))))))
>> +
>> +  (let ((port (make-custom-binary-output-port "buffering-output-port"
>> +                                              write #f #f flush)))
>> +    (setvbuf port _IONBF)
>> +    port))
>> +
>
> Why not just set to _IOFBF and let Guile 2.2's buffering handle it?

Because we want controlled buffering when writing (we need to flush
pending output when we’re done writing the RPC request), and no
buffering at all when reading.

In C/C++ the way to do that is to have unbuffered streams and to do
application-level buffering by allocating output buffers of the right
size.

Thoughts?

Ludo’.