SIGINFO and pthreads

[Maxim Konovalov]

Daniel,

On Thu, 8 Jun 2006, 18:52-0400, Daniel Eischen wrote:

> On Thu, 8 Jun 2006, Maxim Konovalov wrote:
>
> > On Thu, 8 Jun 2006, 12:18-0400, Mikhail Teterin wrote:
> >
> > > четвер 08 червень 2006 00:17, Maxim Konovalov написав:
> > > > Inline it if it's small.  Mailman strips most attachments.
> > >
> > > Damn... Yes, it is small -- this is just a demo program. Compile it first
> > > as
> > >
> > >  cc -o t t.c
> > >
> > > Then -- run and try various keyboard signals like Ctrl-C, Ctrl-Z,
> > > Ctrl-T (SIGINFO), or Ctrl-\. (It will not quit on its own, you'll
> > > have to kill it from another prompt.)
> > >
> > > They will all work. Then -- recompile as
> > >
> > >  cc -o t -pthread t.c
> > >
> > > And run... This time around it will ignore the Ctrl-T, while
> > > continuing to respond to others.
> > >
> > > > libpthread uses SIGINFO for dumping thread information to a file but
> > > > looking over the code it seems it does allow to use SIGINFO to the
> > > > app.
> > >
> > > I'd like to be able to disable the debugging feature or, at least,
> > > force it to call my signal-handler AS EXPECTED AND DOCUMENTED, after
> > > it is done with its own dumping.
> >
> > A funny thing your test program does work if you run it as
> >
> > LIBPTHREAD_DEBUG=yes ./t
> >
> > Try this patch:
>
> [ ... ]
>
> > For the first glance and quick test this check is not needed as we
> > dump threads in already installed for SIGINFO _thr_sig_handler().  Of
> > course we need our libpthreads experts review.
>
> Yes, that is a correct patch (remove the commented out section).
> Please go ahead and commit!

There is still a problem if user decided to SIG_IGN or SIG_DFL
SIGINFO.  In this case threads dump stops working.  I don't know how
important this fuctionality is so here is a more aggressive patch:

Index: thread/thr_private.h
===================================================================
RCS file: /home/ncvs/src/lib/libpthread/thread/thr_private.h,v
retrieving revision 1.126
diff -u -p -r1.126 thr_private.h
--- thread/thr_private.h	29 Mar 2006 05:38:19 -0000	1.126
+++ thread/thr_private.h	9 Jun 2006 12:17:51 -0000
@@ -1317,4 +1317,11 @@ int 	__sys_poll(struct pollfd *, unsigne
 int	__sys_msync(void *, size_t, int);
 #endif

+static __inline int
+_thr_dump_enabled(void)
+{
+
+	return ((_thr_debug_flags & DBG_INFO_DUMP) != 0);
+}
+
 #endif  /* !_THR_PRIVATE_H */
Index: thread/thr_sig.c
===================================================================
RCS file: /home/ncvs/src/lib/libpthread/thread/thr_sig.c,v
retrieving revision 1.84
diff -u -p -r1.84 thr_sig.c
--- thread/thr_sig.c	6 Mar 2006 05:02:28 -0000	1.84
+++ thread/thr_sig.c	9 Jun 2006 12:18:15 -0000
@@ -98,12 +98,6 @@ static int sigproptbl[NSIG] = {
 #define DBG_MSG(x...)
 #endif

-static __inline int
-_thr_dump_enabled(void)
-{
-	return ((_thr_debug_flags & DBG_INFO_DUMP) != 0);
-}
-
 /*
  * Signal setup and delivery.
  *
Index: thread/thr_sigaction.c
===================================================================
RCS file: /home/ncvs/src/lib/libpthread/thread/thr_sigaction.c,v
retrieving revision 1.23
diff -u -p -r1.23 thr_sigaction.c
--- thread/thr_sigaction.c	13 Mar 2006 00:59:51 -0000	1.23
+++ thread/thr_sigaction.c	9 Jun 2006 12:40:31 -0000
@@ -75,7 +75,7 @@ _sigaction(int sig, const struct sigacti
 		 * Check if the kernel needs to be advised of a change
 		 * in signal action:
 		 */
-		if (act != NULL && sig != SIGINFO) {
+		if (act != NULL) {

 			newact.sa_flags |= SA_SIGINFO;

@@ -91,6 +91,16 @@ _sigaction(int sig, const struct sigacti
 				 */
 				newact.sa_handler = (void (*) ())_thr_sig_handler;
 			}
+			/*
+			 * Install libpthread signal handler wrapper
+			 * for SIGINFO signal if threads dump enabled
+			 * even if a user set the signal handler to
+			 * SIG_DFL or SIG_IGN.
+			 */
+			if (sig == SIGINFO && _thr_dump_enabled()) {
+				newact.sa_handler =
+				    (void (*) ())_thr_sig_handler;
+			}
 			/* Change the signal action in the kernel: */
 			if (__sys_sigaction(sig, &newact, NULL) != 0) {
 				_thread_sigact[sig - 1] = oldact;
%%%

-- 
Maxim Konovalov