;;; Copyright (c) 1993 by Olin Shivers.
;;; Signal handler system

;;; The principal trickiness here is that we have to interface to Unix signals
;;; *through* an intermediate interface, the S48 vm's idea of interrupts.
;;; So there is a difference between delivering a signal to the underlying
;;; Unix process and delivering it to the program that runs on the VM.
;;;
;;; One effect is that we have two separate codes for the same thing -- the
;;; Unix signal code, and the S48 interrupt value. E.g., SIGNAL/TSTP and
;;; INTERRUPT/TSTP.

;;; These system calls can return EINTR or restart. In order for the S48 vm's
;;; interrupt system to detect a signal and invoke the handler, they *must*
;;; return EINTR, and this must cause a return from C to Scheme.
;;;
;;; open close dup2 accept connect
;;; read recv recvfrom recvmsg
;;; write send sendto sendmsg
;;; select
;;; wait
;;; fcntl* ioctl
;;; sigsuspend
;;; HP-UX, but I don't use: poll lockf msem_lock msgsnd msgrcv semop
;;; 
;;; * Only during a F_SETLKW
;;;
;;; From rts/interrupt.scm (package interrupts, interface interrupts-interface)
;;;     WITH-INTERRUPTS INTERRUPT-HANDLERS SET-ENABLED-INTERRUPTS! 
;;;	ENABLED-INTERRUPTS
;;; Must define WITH-INTERRUPTS* and WITH-INTERRUPTS.

(foreign-source
  "extern int errno;"
  ""
  "/* Make sure foreign-function stubs interface to the C funs correctly: */"
  "#include \"sighandlers1.h\""
  "" "")

;;; Map a Unix async signal to its S48 interrupt value.
;;; -1 => Not defined.
(define-foreign %signal->interrupt (sig2interrupt (integer sig))
  integer)

(define (signal->interrupt sig)
  (let ((int (%signal->interrupt sig)))
    (if (>= int 0) int
	(error "Unix signal has no Scheme 48 interrupt." sig))))


(define (interrupt-set . interrupts)
  (let lp ((ints interrupts) (ans 0))
    (if (pair? ints)
	(lp (cdr ints) (bitwise-ior ans (arithmetic-shift 1 (- (car ints) 1))))
	ans)))

(define-simple-syntax (with-enabled-interrupts mask body ...)
  (with-interrupts mask (lambda () body ...)))

(define with-enabled-interrupts* with-interrupts)


;;; Get/Set signal handlers
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; When you set a signal's handler to "default," if the default for that
;;; signal is something other than "ignore," we actually install this guy.
;;; When he is called by the S48 interrupt system, he'll magically make
;;; the default action happen (by calling C code that *really* sets the
;;; handler to SIGDFL, and then re-sending the signal). This basically
;;; terminates the process, since if the default isn't "ignore," it's always
;;; "terminate" of some kind. Doing it this way means the exit code given
;;; to our waiting parent proc correctly reflects how we died, and also
;;; makes the core dump happen if it should. Details, details.

(define-foreign %do-default-sigaction (do_default_sigaction (fixnum signal))
  ignore)

;;; This gives the default handler for each signal.
(define default-handler-vec
  (initialize-vector 32 (lambda (sig)
			  ;; This is the guy to call when you want signal
			  ;; SIG handled in the default manner.
			  (if (memv sig signals-ignored-by-default)
			      (lambda (enabled-interrupts) #f)
			      (lambda (enabled-interrupts)
				(%do-default-sigaction sig))))))


;;; HANDLER is #f (ignore), #t (default), or a procedure taking an integer
;;; argument. The interrupt is delivered to a procedure by (1) setting the
;;; ENABLED-INTERRUPTS register to 0 (i.e., blocking all interrupts), and (2)
;;; applying the procedure to the previous value of the ENABLED-INTERRUPTS
;;; register. If the procedure returns normally (i.e., it doesn't throw to a
;;; continuation), the ENABLED-INTERRUPTS register will be restored to its
;;; previous value.

(define (set-signal-handler! sig handler)
  (let ((nhandler (if (eq? handler #t)	; Get SIG's default handler.
		      (vector-ref default-handler-vec sig)
		      handler))
	(int (signal->interrupt sig)))
    (with-enabled-interrupts 0
      (let ((ohandler (vector-ref interrupt-handlers int)))
	(vector-set! interrupt-handlers int nhandler)
	ohandler))))

(define (signal-handler sig)
  (vector-ref interrupt-handlers (signal->interrupt sig)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Set the Unix signal handler. One doesn't usually use this; one usually
;;; uses the S48 VM's interrupt system.
;;; HANDLER-CODE: 0 => ignore, 1 => default, 2 => S48 VM
;;; Returns equivalent code, additionally 3 => other handler.
;;; Raises an error exception if there's a problem.

(define (%set-unix-signal-handler! sig handler-code)
  (check-arg (lambda (x) (and (integer? sig) (< 0 sig 32)))
	     sig
	     %set-unix-signal-handler!)
  (check-arg (lambda (x) (and (integer? handler-code) (<= 0 handler-code 2)))
	     handler-code
	     %set-unix-signal-handler!)
  (let retry ()
    (receive (err old-hc) (%%set-unix-signal-handler! sig handler-code)
      (cond ((not err) old-hc)
	    ((= err errno/intr) (retry))
	    (else (errno-error err %set-unix-signal-handler! sig handler-code))))))

(define-foreign %%set-unix-signal-handler!
  (scsh_set_sig (fixnum sig) (fixnum hc) (fixnum flags))
  desc		; #f or errno
  integer	; previous handler-code
  integer)	; previous handler flags

(define (%unix-signal-handler sig)
  (check-arg (lambda (x) (and (integer? sig) (< 0 sig 32)))
	     sig
	     %unix-signal-handler)
  (let retry ()
    (receive (err hc flags) (%%unix-signal-handler sig)
      (cond ((not err) hc)
	    ((= err errno/intr) (retry))
	    (else (errno-error err %unix-signal-handler sig))))))

(define-foreign %%unix-signal-handler (scsh_get_sig (fixnum sig))
  desc		; #f or errno
  integer	; previous handler-code
  integer)	; previous handler flags

(define-foreign %install-unix-scsh-handlers (install_scsh_handlers) ignore)

(define-foreign %%get-int-handlers (get_int_handlers) desc)

(define (%install-scsh-handlers)
  (do ((sig 32 (- sig 1)))
      ((< sig 0))
    (let ((i (%signal->interrupt sig)))
      (if (not (or (= i -1) (= sig signal/int) (= sig signal/alrm)))
	  (vector-set! interrupt-handlers i
		       (vector-ref default-handler-vec sig))))))