Unix signal handling in (common) lisp - lisp

Question

I've done a bit of research on this subject and am turning up blanks. There seem to be implementation-dependent ways of doing Unix signal handling in Common Lisp, but is there a package that gives a cross-implementation way of doing signal handling?
I would mainly like to listen for SIGINT and do a graceful shutdown in my app. I'm using Clozure CL 1.7 on linux...like mentioned, it would be great for a package for this, but if I have to resort to implementation-specific code, that's fine.
I'm also not completely married to using SIGINT (although it's ideal). I can use another signal if needed.
If this is going to be messy, does anyone have any other suggestions for gracefully shutting down a lisp app from outside the app? One idea I had is to create a file the app monitors for, and if it detects the file, it shuts down...kind of hacky, though.
Thanks!

Answer 1

Although out of ignorance I was originally skeptical of Daimrod's comment (first comment under the question) about using CFFI, I looked around a bit more and found http://clozure.com/pipermail/openmcl-devel/2010-July/011675.html. I adapted it to use CFFI and have confirmed this works on SBCL/CCL/clisp (probably others) on linux pretty damn well:
(defmacro set-signal-handler (signo &body body)
(let ((handler (gensym "HANDLER")))
`(progn
(cffi:defcallback ,handler :void ((signo :int))
(declare (ignore signo))
,#body)
(cffi:foreign-funcall "signal" :int ,signo :pointer (cffi:callback ,handler)))))
(set-signal-handler 2
(format t "Quitting lol!!!11~%")
;; fictional function that lets the app know to quit cleanly (don't quit from callback)
(signal-app-to-quit))
Note that from what I understand, whatever is in the body of the callback must be short and sweet! No lengthy processing. In the linked article, the macro actually creates a separate thread just for handling the signal, which is overkill for my purposes, since I'm just setting a global variable from nil to t and returning.
Anyway, hopefully this is helpful to others!

Answer 2

I can't find a general library for signal handling either. However, Slime implements "create a custom SIGINT handler" for most Lisp implementations. By looking at the CCL case of that code, I found ccl:*break-hook*. ccl:*break-hook* is not in the documentation, but the commit it was introduced in is located here.
This trivial example code works on my system (CCL 1.8, linux x86):
(setf ccl:*break-hook*
(lambda (cond hook)
(declare (ignore cond hook))
(format t "Cleaning up ...")
(ccl:quit)))
After this code is entered into a non-Slime REPL, sending SIGINT will cause the program to print "Cleaning up ..." and exit.

Answer 3

This is a late answer, but for anybody else searching for this, have a look at trivial-signal, available on Quicklisp. This is based on CFFI.
Example
(signal-handler-bind ((:int (lambda (signo)
(declare (ignorable signo))
...handler...)))
...body...)

Answer 4

If you use SBCL, you cannot change the signal mask without causing SBCL to crash. Ask nyef about his tips on how to fix SBCL...

Answer 5

So there is trivial-signal as mentioned. Here's how I catch a C-c in my code:
(handler-case
(my-app-main-function)
;; AFAIK trivial-signal is supposed to handle the implementation differences.
(#+sbcl sb-sys:interactive-interrupt
#+ccl ccl:interrupt-signal-condition
#+clisp system::simple-interrupt-condition
#+ecl ext:interactive-interrupt
#+allegro excl:interrupt-signal
() (progn
(format *error-output* "Aborting.~&")
(exit)))
(error (c) (format t "Woops, an unknown error occured:~&~a~&" c)))