Re: signal blocking?

[Byron Rakitzis <byron>]

Ok, it seems this application of signal handlers is as "real" as
they get.

re: putting a "return" in the signal handler. This is not going to
do a lot of good, since setting $status never changes the value of
errno in any case. I have specifically made signal handler invocations
different from function invocations (no "return" is allowed) so
that one could realize that it is not a very meaningful thing to
set $status in a signal handler.

It seems that the fundamental limitation here is not the ability
of rc to queue signals inside a signal handler, but rather the
system call/errno interface. read() returns a -1 on failure---any
kind of failure---and then you have to check errno to see what the
error really was. When a signal handler buggers the value of errno
you are really done for.

Therefore my initial reaction would be to have a signal handler do
a save/restore of errno, and preserve the v7 semantics of rc signal
handlers; I don't really feel like changing the way signals are
done in rc right now. It still seems like too much work, and the
current problem can be solved with this code:

; fn sigwinch {handle}
; fn handle {
	fn sigwinch
	stty
	fn sigwinch {handle}
}

(I just tried this on a NeXT and a Sun, with a save/restore of
errno in fn_handler, and a window-size-change on a terminal window)

Anyway, here's a context diff for fn.c:

*** fn.c.orig	Sun Mar 29 10:32:36 1992
--- fn.c	Wed Apr  8 10:39:35 1992
***************
*** 4,9 ****
--- 4,10 ----
  */
  
  #include <signal.h>
+ #include <errno.h>
  #include "rc.h"
  #include "sigmsgs.h"
  
***************
*** 84,91 ****
--- 85,94 ----
  static void fn_handler(int s) {
  	List *dollarzero;
  	Estack e;
+ 	int olderrno;
  	if (s < 1 || s >= NUMOFSIGNALS)
  		panic("unknown signal");
+ 	olderrno = errno;
  	dollarzero = nnew(List);
  	dollarzero->w = signals[s][0];
  	dollarzero->n = NULL;
***************
*** 94,99 ****
--- 97,103 ----
  	walk(handlers[s], TRUE);
  	varrm("*", TRUE);
  	unexcept(); /* eVarstack */
+ 	errno = olderrno;
  }
  
  /*