2013-10-18

Enbug

Even though 0.4.10 has just been released today I found a critical (caused SEGV) bug.... ;-(

The code is like this;
(import (rnrs))
(define save #f)
(let* ([p (make-custom-binary-input/output-port
    "custom in"
    (lambda (bv start end)
      (bytevector-u8-set! bv start 7)
      (set! save bv)
      1)
    (lambda (bv start end)
      1)
    #f #f #f)])
  (put-u8 p 10)
  (flush-output-port p)
  (get-u8 p)
  (close-port p))
(print "SEGV!!")
(print save)
I've never seen such use case however SEGV is worse than unexpected result (it is unexpected but you know...).  I know exactly why this happens and how to resolve this. The reason why I'm writing this is making this for my admonition.

The reason why this happens is because it's using stack allocated bytevector for *invalid* performance optimisation. I was so eager to make Sagittarius uses less memory so did this. However once C code calls Scheme code then there are always possibilities that the passed value would be saved out side of the scope. This is the typical case.

I just need to say this to myself, DON'T BE LESS CONSIDERED!!!

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