I know SBCL's WITH-TIMEOUT cannot nest, I learn this from GBBopen's portable-threads.lisp [1], and it also give a nested version SBCL's WITH-TIMEOUT, much shorter than yours:
#+sbcl (defmacro with-timeout ((seconds &body timeout-body) &body timed-body) (let ((tag-sym (gensym)) (timer-sym (gensym))) `(block ,tag-sym (let ((,timer-sym (sb-ext:make-timer #'(lambda () (return-from ,tag-sym (progn ,@timeout-body)))))) (sb-ext:schedule-timer ,timer-sym ,seconds) (unwind-protect (progn ,@timed-body) (sb-ext:unschedule-timer ,timer-sym))))))
I didn't use this version simply because I think the WITH-TIMEOUT form in usocket's SOCKET-CONNECT has no chance to be nested.
--binghe
在 2011-3-29，04:35， Nikodemus Siivola 写道：
2011/3/28 Chun Tian (binghe) binghe.lisp@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 () ,@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