emacsclient -t should not suspend Emacs server

* lisp.h, sysdep.c (block_tty_out_signal, unblock_tty_out_signal):
New functions.
* term.c (init_tty): Use them instead of rolling our own code.
* sysdep.c (tcsetpgrp_without_stopping): Likewise.  Here, this
switches from 'signal' to 'pthread_sigmask', which is safer in
multithreaded applications.
* term.c (Fresume_tty): Don't bother dissociating if O_IGNORE_CTTY,
which has already arranged for that.
(dissociate_if_controlling_tty): If setsid fails, fall back on TIOCNOTTY.
This is the main part of the bug fix.

Fixes: debbugs:13387

1 files changed, 23 insertions, 3 deletions

diff --git a/src/sysdep.c b/src/sysdep.c
index 049eb85afe5..158d2f73eec 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -714,6 +714,27 @@ init_foreground_group (void)
   inherited_pgroup = getpid () == pgrp ? 0 : pgrp;
 }
 
+/* Block and unblock SIGTTOU.  */
+
+void
+block_tty_out_signal (void)
+{
+#ifdef SIGTTOU
+  sigset_t blocked;
+  sigemptyset (&blocked);
+  sigaddset (&blocked, SIGTTOU);
+  pthread_sigmask (SIG_BLOCK, &blocked, 0);
+#endif
+}
+
+void
+unblock_tty_out_signal (void)
+{
+#ifdef SIGTTOU
+  pthread_sigmask (SIG_SETMASK, &empty_mask, 0);
+#endif
+}
+
 /* Safely set a controlling terminal FD's process group to PGID.
    If we are not in the foreground already, POSIX requires tcsetpgrp
    to deliver a SIGTTOU signal, which would stop us.  This is an
@@ -725,11 +746,10 @@ static void
 tcsetpgrp_without_stopping (int fd, pid_t pgid)
 {
 #ifdef SIGTTOU
-  signal_handler_t handler;
   block_input ();
-  handler = signal (SIGTTOU, SIG_IGN);
+  block_tty_out_signal ();
   tcsetpgrp (fd, pgid);
-  signal (SIGTTOU, handler);
+  unblock_tty_out_signal ();
   unblock_input ();
 #endif
 }