[usocket-devel] [drakma-devel] [patch] Resubmit drakma timeout for sbcl.
Nikodemus Siivola
nikodemus at random-state.net
Mon Mar 28 20:35:14 UTC 2011
2011/3/28 Chun Tian (binghe) <binghe.lisp at gmail.com>:
> Today I think out another way to solve the SBCL connection timeout issue, I wrap a
> SB-EXT:WITH-TIMEOUT on SB-BSD-SOCKET:SOCKET-CONNNECT [1], and the result work seems working well:
That's along the lines I was thinking off, except that
SB-EXT:WITH-TIMEOUT is a broken construct. (Soon to be deprecated, in
all likelihood.)
Consider this:
(with-timeout 1.0 (handler-case (with-timeout 4.0 (sleep 2))
(sb-ext:timeout ())))
which is to say that you cannot distinguish an outer timeout from an
inner one, which is bad.
You need something like this, instead:
(defmacro with-timeout-handler ((seconds timeout-form) &body body)
"Runs BODY as an implicit PROGN with timeout of SECONDS. If
timeout occurs before BODY has finished, BODY is unwound and
TIMEOUT-FORM is executed with its values returned instead.
Note that BODY is unwound asynchronously when a timeout occurs,
so unless all code executed during it -- including anything
down the call chain -- is asynch unwind safe, bad things will
happen. Use with care."
(alexandria:with-gensyms (exec unwind timer timeout block)
`(block ,block
(tagbody
(flet ((,unwind ()
(go ,timeout))
(,exec ()
, at body))
(declare (dynamic-extent #',exec #',unwind))
(let ((,timer (sb-ext:make-timer #',unwind)))
(declare (dynamic-extent ,timer))
(sb-sys:without-interrupts
(unwind-protect
(progn
(sb-ext:schedule-timer ,timer ,seconds)
(return-from ,block
(sb-sys:with-local-interrupts
(,exec))))
(sb-ext:unschedule-timer ,timer)))))
,timeout
(return-from ,block ,timeout-form)))))
with which
(with-timeout-handler (1.0 :outer) (with-timeout-handler (4.0
:inner) (sleep 10.0) :ok))
does the right thing.
Gods, I hate asynch timeouts. Is there a sane way to tell connect() to
time out without needing SIGALRM?
Cheers,
-- Nikodemus
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