Ludovic Courtès escreveu:
> Hello,
>
> Andy Wingo <[EMAIL PROTECTED]> writes:
>
>> ERROR: srfi-18.test: thread-start!:
>> thread activates only after start
>> - arguments: ((syntax-error "memoization"
>> "In file ~S, line ~S: ~A ~S in expression ~S."
>> ("/home/lilydev/vc/guile/srfi/srfi-18.scm" 135
>> "Bad binding" ct
>> (let (ct (current-thread))
>> [EMAIL PROTECTED] (or (hashq-ref
>> thread-exception-handlers ct)
>> (hashq-set! thread-exception-handlers ct
>> (list initial-handler))))) #f))
>
> I'm seeing this as well, but it's a [EMAIL PROTECTED]' here (single-binding
> `let's
> are memoized as [EMAIL PROTECTED]'):
>
> ((syntax-error "memoization"
> "In file ~S, line ~S: ~A ~S in expression ~S."
> ("/home/ludo/src/guile/srfi/srfi-18.scm" 138
> "Bad binding"
> ct
> ([EMAIL PROTECTED] (ct (#<variable b7d28110 value:
> #<primitive-procedure current-thread>>))
> ([EMAIL PROTECTED] (#<variable b7d2ad88 value:
> #<primitive-procedure hashq-ref>>
> #<variable 839df08 value:
> #<weak-key-hash-table 1/31>> [EMAIL PROTECTED])
> (#<variable b7d2adc0 value: #<primitive-procedure
> hashq-set!>> #<variable 839df08 value: #<weak-key-hash-table 1/31>> [EMAIL
> PROTECTED] (#<variable b7d2c498 value: #<primitive-procedure list>>
> #<variable 839d130 value: #<procedure initial-handler (obj)>>))
> )))
> #f))
>
> It can be reproduced, but very infrequently, with this program:
>
> (use-modules (ice-9 threads))
>
> (define (foo x y)
> (let ((z (+ x y)))
> (let ((a (+ z 1)))
> (let ((b (- a 2)))
> (let ((c (* b 3)))
> c)))))
>
> (define (entry)
> (foo 1 2))
>
> (for-each (lambda (i) (make-thread entry))
> (iota 123))
>
> My explanation is that the `let*' memoizer, aka. `scm_m_letstar ()', is
> not thread-safe; it's clearly not atomic, and it's of course not
> protected by a mutex or so.
Is that the only one?
SCM
scm_m_let (SCM expr, SCM env)
...
/* plain let */
SCM rvariables;
SCM inits;
transform_bindings (bindings, expr, &rvariables, &inits);
{
const SCM new_body = m_body (SCM_IM_LET, SCM_CDR (cdr_expr));
const SCM new_tail = scm_cons2 (rvariables, inits, new_body);
SCM_SETCAR (expr, SCM_IM_LET);
// ****!!!
SCM_SETCDR (expr, new_tail);
What happens if another thread tries to evaluate expr at the place marked
****!!! ?
At the very least, we should have an atomic SCM_SETCELL() which overwrites car
and
cdr atomically.
--
Han-Wen Nienhuys - [EMAIL PROTECTED] - http://www.xs4all.nl/~hanwen
