I know at least one CL platform, LispWorks, has some related API
(HCL:ADD-SPECIAL-FREE-ACTION) [1], and I want to use it in my UDP
applications. Just don't know if this will be a common feature to be
considered by usocket itself.
It doesn't need to be applied to other backends in general, however,
it does need to be applied to all implementations which make direct
use of the handles (non-lisp objects) supplied by the operating
system.
The usual terminology for this kind of stuff is "finalizers". What
you
could do, is to add a finalizer that signals a warning if a socket
object is going to be garbage collected that wasn't closed
previously.
Right. However, implementations which provide objects for this purpose
should take care of this themselves because usocket uses the
implementation supplied sockets. Only in those cases where such
guarantees are missing, usocket needs to take additional measures.
This includes LispWorks, but additional investigation will turn up if
this is the only implementation affected.
I'm quite sure that only UDP stuff being affected (which haven't been
merged into USOCKET). For TCP, the CL implementation itself will take
good care of TCP streams and close the socket fd when streams being
GCed.
After more investigation, I think there're two implementations of five
(CMUCL, ECL/SBCL, CCL, Allegro CL, LispWorks) need consider this
issue: LispWorks and CMUCL. They both operate on raw socket fd.
For LispWorks, I've done my idea on USOCKET-UDP: add a special free
action on DATAGRAM-USOCKET, when it's getting GCed, SOCKET-CLOSE will
be called on it, and I have to add a new CLOSED-P slot for LispWorks
on DATAGRAM-USOCKET to avoid multiple call of SOCKET-CLOSE. See this:
http://cl-net-snmp.svn.sourceforge.net/viewvc/cl-net-snmp/usocket-udp/trunk/usocket-lispworks.lisp?sortby=rev&r1=449&r2=560&pathrev=560
Test on LispWorks shows above code can work: I create many unconnected
DATAGRAM-USOCKET instances but not assign them to any variable. After
some time and make sure no */**/*** still point to these instances, do
a (HCL:GC-ALL) can get all these socket-fd be closed correctly. I
think the issue solved (on LispWorks).
Don't know if CMUCL has related function to do the same thing (yet).
--
binghe
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