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second attempt at forbidding self-calls, with a long explanation why its forbidden, which is actually a sketch for how to make it work...

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svn: r13376
This commit is contained in:
Eli Barzilay 2009-02-03 13:29:33 +00:00
parent 3d04e81fa0
commit a2537d7dc9
1 changed files with 11 additions and 9 deletions
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20
collects/scheme/sandbox.ss
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@ -615,6 +615,7 @@
(define uncovered #f)
(define input-ch (make-channel))
(define result-ch (make-channel))
(define busy-sema (make-semaphore 1))
(define input #f)
(define output #f)
(define error-output #f)
@ -705,16 +706,17 @@
(cond [terminated? => raise]
[(not user-thread)
(error 'sandbox "internal error (user-thread is #f)")]
;; try to put the expression in, but if can't then it means that the
;; evaluator is calling itself -- there is no simple way to make this
;; work, so throw an error
;; FIXME: the commented-out part creates a race, because the evaluator
;; thread might not be waiting on input-ch, yet; it might be
;; in between sending the previous result and waiting for the
;; next expression
[(not (sync #|/timeout 0|# (channel-put-evt input-ch expr)))
;; use a semaphore to know when we're currently in an evaluation, to
;; prevent the evaluator from calling itself (it will deadlock, and
;; there is no simple way to avoid it -- will require making a stream
;; of inputs sent to the user context, queueing them as they come in,
;; and for each one register a channel for a reply -- and this will
;; consume resources outside the user context)
[(not (sync/timeout 0 busy-sema))
(error 'evaluator "nested evaluator call with: ~e" expr)]
[else (let ([r (get-user-result)])
[else (channel-put input-ch expr)
(let ([r (get-user-result)])
(semaphore-post busy-sema)
(cond [(eof-object? r) (terminate+kill! #t #t)]
[(eq? (car r) 'exn) (raise (cdr r))]
[else (apply values (cdr r))]))]))