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.
I can't think of any simple fix. `scm_m_letstar ()' could be made
atomic by having it duplicate the input list instead of modifying it
directly; it could then atomically update the input. However,
allocating cells during memoization wouldn't be a good idea
performance-wise.
Thanks,
Ludo'.
