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added a clarifying example for how limits interact

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svn: r12864
This commit is contained in:
Eli Barzilay 2008-12-15 22:15:52 +00:00
parent 43124c2ec5
commit e5027cb7b0
1 changed files with 17 additions and 1 deletions
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18
collects/scribblings/reference/sandbox.scrbl
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@ -521,7 +521,23 @@ the highest custodian that refers to it. This means that if you
inspect a value that sandboxed evaluation returns outside of the
sandbox, your own custodian will be charged for it. To ensure that it
is charged back to the sandbox, you should remove references to such
values when the code is done inspecting it.}
values when the code is done inspecting it.
This policy has an impact on how the sandbox memory limit interacts
with the the per-expression limit specified by
@scheme[sandbox-eval-limits]: values that are reachable from the
sandbox, as well as from the interaction will count against the
sandbox limit. For example, in the last interaction of this code,
@schemeblock[
(define e (make-evaluator 'scheme/base))
(e '(define a 1))
(e '(for ([i (in-range 20)]) (set! a (cons (make-bytes 500000) a))))
]
the memory blocks are allocated within the interaction limit, but
since they're chained to the defined variable, they're also reachable
from the sandbox --- so they will count against the sandbox memory
limit but not against the interaction limit (more precisely, no more
than one block counts against the interaction limit).}
@defparam[sandbox-eval-limits limits