Re: [PATCH] Replacement for the sigs_to_ignore hack in timeout.c

[Eric Blake]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

According to Eric Blake on 10/10/2008 7:15 AM:
>> I've wanted to get rid of "signal" uses for ages.
>> Are you interested in doing it?
> 
> Yes, I'll tackle this.

Round 1: csplit.  The use of signal here mirrors what Bruno's fatal-signal
module in gnulib provides, although the set of signals masked is
different.  Which would you prefer, a patch that swaps over to
fatal-signal usage (leaving at least SIGPOLL and SIGALRM unprotected), or
this patch?  I'm kind of leaning towards simplifying this file by using
fatal-signal, but had already written this, and wanted some feedback.

I think the SA_NODEFER | SA_RESETHAND combo is correct here; the handler
is for one-shot cleanup of temporary files, so we want the handler to be
reset to SIG_DFL on nested signal.  POSIX requires that portable programs
request SA_NODEFER alongside SA_RESETHAND, but we also include the signal
in the block mask, so a nested signal won't fire until after the handler
completes.  I think we are safe assuming that upon return from a signal
handler, a signal that is no longer blocked will fire.

$ git pull git://repo.or.cz/coreutils/ericb.git signal

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAkj0HagACgkQ84KuGfSFAYDlqgCgjxLJHUN0KhgXmMEaejyBCgxm
sBEAnRFK4bdSrNxKpTvtR6KBQkBbcsCY
=PBR6
-----END PGP SIGNATURE-----

>From 8c6dca936672e76f67c09e669bca803e80d64ef7 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Mon, 13 Oct 2008 22:04:51 -0600
Subject: [PATCH] csplit: prefer sigaction over signal

* bootstrap.conf (gnulib_modules): Import sigaction.
* src/csplit.c (sigprocmask, siginterrupt) [SA_NOCLDSTOP]: Delete
workarounds.
(interrupt_handler, main): Drop use of signal.  Rely on sigaction
to block fatal signal during cleanup, and to restore it to default
in case of nested signals.

Signed-off-by: Eric Blake <address@hidden>
---
 bootstrap.conf |    2 +-
 src/csplit.c   |   30 ++++--------------------------
 2 files changed, 5 insertions(+), 27 deletions(-)

diff --git a/bootstrap.conf b/bootstrap.conf
index b3eec48..6405955 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -84,7 +84,7 @@ gnulib_modules="
        safe-read same
        save-cwd savedir savewd
        selinux-at
-       settime sig2str ssize_t stat-macros
+       settime sig2str sigaction ssize_t stat-macros
        stat-time stdbool stdlib-safer stpcpy
        stpncpy
        strftime
diff --git a/src/csplit.c b/src/csplit.c
index 55489c3..b50a650 100644
--- a/src/csplit.c
+++ b/src/csplit.c
@@ -34,17 +34,6 @@
 #include "stdio--.h"
 #include "xstrtol.h"
 
-/* Use SA_NOCLDSTOP as a proxy for whether the sigaction machinery is
-   present.  */
-#ifndef SA_NOCLDSTOP
-# define SA_NOCLDSTOP 0
-# define sigprocmask(How, Set, Oset) /* empty */
-# define sigset_t int
-# if ! HAVE_SIGINTERRUPT
-#  define siginterrupt(sig, flag) /* empty */
-# endif
-#endif
-
 /* The official name of this program (e.g., no `g' prefix).  */
 #define PROGRAM_NAME "csplit"
 
@@ -238,12 +227,10 @@ xalloc_die (void)
 static void
 interrupt_handler (int sig)
 {
-  if (! SA_NOCLDSTOP)
-    signal (sig, SIG_IGN);
-
   delete_all_files (true);
-
-  signal (sig, SIG_DFL);
+  /* The signal has been reset to SIG_DFL, but blocked during this
+     handler.  Force the default action of this signal once the
+     handler returns and the block is removed.  */
   raise (sig);
 }
 
@@ -1421,7 +1408,6 @@ main (int argc, char **argv)
       };
     enum { nsigs = sizeof sig / sizeof sig[0] };
 
-#if SA_NOCLDSTOP
     struct sigaction act;
 
     sigemptyset (&caught_signals);
@@ -1434,19 +1420,11 @@ main (int argc, char **argv)
 
     act.sa_handler = interrupt_handler;
     act.sa_mask = caught_signals;
-    act.sa_flags = 0;
+    act.sa_flags = SA_NODEFER | SA_RESETHAND;
 
     for (i = 0; i < nsigs; i++)
       if (sigismember (&caught_signals, sig[i]))
        sigaction (sig[i], &act, NULL);
-#else
-    for (i = 0; i < nsigs; i++)
-      if (signal (sig[i], SIG_IGN) != SIG_IGN)
-       {
-         signal (sig[i], interrupt_handler);
-         siginterrupt (sig[i], 1);
-       }
-#endif
   }
 
   split_file ();
-- 
1.6.0.2