[RFC] Don't immediately SIGTERM the child of "target remote |".

Doug Evans
2011-11-24T00:01:14Z

Hi.

While testing a patch to allow gdbserver to communicate over stdio
(e.g. target remote | gdbserver ...)
I found that several tests from the testsuite were left running
and traced it to gdb SIGTERMing gdbserver when the connection is closed.

We could add a SIGTERM handler to gdbserver
but I'm starting with this patch.
I don't understand why gdb kills the child at all.
In a properly written child connection, closing stdin should be a
sufficient signal for the child to know to shutdown.

AFAICT The kill() call was added in cvs revision 1.2 with the log entry:
Replace ../include/wait.h with gdb_wait.h.
Blech.

Alas I can't remove this kill(SIGTERM) call
for fear of breaking something so I'm trying a
compromise and only killing the child after some timeout.

Comments?

I borrowed the SA_RESTART handling from other places in gdb.
I don't actually know that this works (i.e. the alarm call
will wake up waitpid) on systems without SA_RESTART,
and I don't know if alarm() is portable enough
(there are no current uses of it AFAICT).

2011-11-23 Doug Evans <dje@google.com>

* ser-pipe.c (sigalrm_handler): New function.
(pipe_close): Don't immediately send SIGTERM to the child.
Give it awhile to cleanly shutdown, but don't wait forever.

Index: ser-pipe.c
===================================================================
RCS file: /cvs/src/src/gdb/ser-pipe.c,v
retrieving revision 1.32
diff -u -p -r1.32 ser-pipe.c
--- ser-pipe.c 4 Mar 2011 19:23:42 -0000 1.32
+++ ser-pipe.c 23 Nov 2011 23:46:55 -0000
@@ -154,6 +154,12 @@ pipe_open (struct serial *scb, const cha
}

static void
+sigalrm_handler (int signo)
+{
+ /* nothing to do */
+}
+
+static void
pipe_close (struct serial *scb)
{
struct pipe_state *state = scb->state;
@@ -163,14 +169,45 @@ pipe_close (struct serial *scb)

if (state != NULL)
{
- int status;
- kill (state->pid, SIGTERM);
+ int rc, status;
+ void (*ofunc) (); /* Previous SIGALRM handler. */
+
+ /* Don't kill the task right away, give it a chance to shut down cleanly.
+ But don't wait forever though. */
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+ {
+ struct sigaction sa, osa;
+ sa.sa_handler = sigalrm_handler;
+ sigemptyset (&sa.sa_mask);
+ sa.sa_flags = 0;
+ sigaction (SIGALRM, &sa, &osa);
+ ofunc = osa.sa_handler;
+ }
+#else
+ ofunc = (void (*)()) signal (SIGALRM, sigalrm_handler);
+#endif
+
+#define PIPE_CLOSE_TIMEOUT 5
+ alarm (PIPE_CLOSE_TIMEOUT);
+
+ rc = -1;
#ifdef HAVE_WAITPID
/* Assume the program will exit after SIGTERM. Might be
useful to print any remaining stderr output from
scb->error_fd while waiting. */
- waitpid (state->pid, &status, 0);
+ rc = waitpid (state->pid, &status, 0);
+#endif
+ if (rc != 0)
+ {
+ kill (state->pid, SIGTERM);
+#ifdef HAVE_WAITPID
+ waitpid (state->pid, &status, 0);
#endif
+ }
+
+ alarm (0);
+ signal (SIGALRM, ofunc);
+
if (scb->error_fd != -1)
close (scb->error_fd);
scb->error_fd = -1;