Hi, Chaitanya
I found the implementation of SB-UNIX:UNIX-FAST-SELECT in SBCL source
tree (src/code/unix.lisp)
;;; Perform the UNIX select(2) system call.
(declaim (inline unix-fast-select))
(defun unix-fast-select (num-descriptors
read-fds write-fds exception-fds
timeout-secs timeout-usecs)
(declare (type (integer 0 #.fd-setsize) num-descriptors)
(type (or (alien (* (struct fd-set))) null)
read-fds write-fds exception-fds)
(type (or null (unsigned-byte 31)) timeout-secs timeout-
usecs))
(flet ((select (tv-sap)
(int-syscall ("select" int (* (struct fd-set)) (* (struct
fd-set))
(* (struct fd-set)) (* (struct
timeval)))
num-descriptors read-fds write-fds exception-
fds
tv-sap)))
(cond ((or timeout-secs timeout-usecs)
(with-alien ((tv (struct timeval)))
(setf (slot tv 'tv-sec) (or timeout-secs 0))
(setf (slot tv 'tv-usec) (or timeout-usecs 0))
(select (alien-sap (addr tv)))))
(t
(unless *interrupts-enabled*
(note-dangerous-select))
(select (int-sap 0))))))
And the Book "UNIX Network Programming Vol 1 (2nd edition)" said about
select() (p. 150):
"Wait forever: return only when one of the specified descriptors is
ready for I/O.
For this, we specify the /timeout/ argument as a null pointer."
So, to make UNIX-FAST-SELECT wait for ever, both TIMEOUT-SECS and
TIMEOUT-USECS must be NIL. I think your patch is right, that's a
usocket bug.
Commited to trunk as r483, thanks very much!
--binghe
On 2008-12-24, at 01:13, Chaitanya Gupta wrote:
> Hi,
>
> On SBCL, providing :timeout NIL to wait-for-input returns
> immediately even when there is no input on any of the provided
> sockets (the documentation says it should wait indefinitely).
>
> Attached is a patch (svn diff) which fixes this, but I am not very
> sure about how sb-unix:unix-fast-select works, so its be best if
> someone who knows better can review it before committing this
> patch. :)
>
> Cheers,
> Chaitanya
>
> Index: backend/sbcl.lisp
> ===================================================================
> --- backend/sbcl.lisp (revision 482)
> +++ backend/sbcl.lisp (working copy)
> @@ -353,7 +353,7 @@
> (1+ (reduce #'max (wait-list-%wait sockets)
> :key #'sb-bsd-sockets:socket-file-
> descriptor))
> (sb-alien:addr rfds) nil nil
> - (when timeout secs) musecs)
> + (when timeout secs) (when timeout musecs))
> (if (null count)
> (unless (= err sb-unix:EINTR)
> (error (map-errno-error err)))
> _______________________________________________
> usocket-devel mailing list
> usocket-devel@common-lisp.net
> http://common-lisp.net/cgi-bin/mailman/listinfo/usocket-devel
--
Chun Tian (binghe)
NetEase.com, Inc.
P. R. China
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