Remove AC_SYS_RESTARTABLE_SYSCALLS and related code

As the Autoconf documentation says, "These days portable programs
[...] should not rely on `HAVE_RESTARTABLE_SYSCALLS', since nowadays
whether a system call is restartable is a dynamic issue, not a
configuration-time issue."

In other words, if we ever rely on HAVE_RESTARTABLE_SYSCALLS, we are
at the mercy of any code that Guile happens to be linked with, because
that code could install a signal handler without the SA_RESTART flag,
and then a Guile system call could unexpectedly return EINTR.

The readline part of this goes back to this problem report:
http://sources.redhat.com/ml/guile/2000-05/msg00177.html; and is an
excellent example of the above paragraph.  It was noted during the
discussion that undefining HAVE_RESTARTABLE_SYSCALLS would fix the
problem, but that solution wasn't adopted - I guess because Guile was
still using cooperative threads then (not pthreads) and so there was a
significant concern (whether founded or not) that not using
restartable syscalls (where available) could lead to a loss of
performance.

Now Guile's default mode of operation is with pthreads, where we
already don't assume that HAVE_RESTARTABLE_SYSCALLS is reliable, so
there is no possible further performance loss.  And in any case we
really have no choice, if we want correct operation.

Thanks to Sylvain Beucler for reporting this and suggesting the fix.

* configure.in (AC_SYS_RESTARTABLE_SYSCALLS): Removed.

* doc/ref/posix.texi (Signals): Remove statement that Guile always
  sets SA_RESTART flag.

* guile-readline/configure.in (GUILE_SIGWINCH_SA_RESTART_CLEARED):
  Remove this setting, together with its test code.
  (HAVE_RL_PRE_INPUT_HOOK): Remove this setting and its code, as no
  longer needed.

* guile-readline/readline.c (sigwinch_enable_restart): Removed.
  (scm_init_readline): Remove setting of rl_pre_input_hook.

* libguile/_scm.h (SCM_SYSCALL): Remove the definition that relies on
  HAVE_RESTARTABLE_SYSCALLS.

* libguile/scmsigs.c (scm_sigaction_for_thread): Don't always set the
  SA_RESTART flag if available.  Update docstring accordingly.
  (scm_init_scmsigs): Remove code that sets SA_RESTART flag for all
  signals.

* THANKS: Add Sylvain.

2 files changed, 0 insertions, 94 deletions

diff --git a/guile-readline/configure.in b/guile-readline/configure.in
index d05356618..f24fc9418 100644
--- a/guile-readline/configure.in
+++ b/guile-readline/configure.in
@@ -54,77 +54,6 @@ dnl install paren matching on the Guile command line (when using
 dnl readline for input), so it's completely optional.
 AC_CHECK_FUNCS(rl_get_keymap)
 
-dnl Check for rl_pre_input_hook.  This is more complicated because on
-dnl some systems (HP/UX), the linker wont let us treat
-dnl rl_pre_input_hook as a function when it really is a function
-dnl pointer.
-
-AC_MSG_CHECKING([for rl_pre_input_hook])
-AC_CACHE_VAL(ac_cv_var_rl_pre_input_hook,
-[AC_TRY_LINK([
-#include <stdio.h>
-#include <readline/readline.h>
-], [
-rl_pre_input_hook = 0;
-],
-ac_cv_var_rl_pre_input_hook=yes,
-ac_cv_var_rl_pre_input_hook=no)])
-AC_MSG_RESULT($ac_cv_var_rl_pre_input_hook)
-if test $ac_cv_var_rl_pre_input_hook = yes; then
-  AC_DEFINE(HAVE_RL_PRE_INPUT_HOOK,1,
-            [Define if rl_pre_input_hook is available.])
-fi
-
-
-AC_MSG_CHECKING(if readline clears SA_RESTART flag for SIGWINCH)
-AC_CACHE_VAL(guile_cv_sigwinch_sa_restart_cleared,
-AC_TRY_RUN([#include <signal.h>
-#include <stdio.h>
-#include <readline/readline.h>
-
-int
-hook ()
-{
-  struct sigaction action;
-
-  sigaction (SIGWINCH, NULL, &action);
-  rl_cleanup_after_signal();
-
-  /* exit with 0 if readline disabled SA_RESTART */
-  exit (action.sa_flags & SA_RESTART);
-}
-
-int
-main ()
-{
-  struct sigaction action;
-
-  sigaction (SIGWINCH, NULL, &action);
-  action.sa_flags |= SA_RESTART;
-  sigaction (SIGWINCH, &action, NULL);
-
-  /* Give readline something to read.  Otherwise, it might hang, for
-     example when run as a background process with job control.
-  */
-  rl_instream = fopen ("/dev/null", "r");
-  if (rl_instream == NULL)
-    {
-      perror ("/dev/null");
-      exit (1);
-    }
-
-  rl_pre_input_hook = hook;
-  readline ("");
-}],
-guile_cv_sigwinch_sa_restart_cleared=yes,
-guile_cv_sigwinch_sa_restart_cleared=no,
-guile_cv_sigwinch_sa_restart_cleared=yes))
-AC_MSG_RESULT($guile_cv_sigwinch_sa_restart_cleared)
-if test $guile_cv_sigwinch_sa_restart_cleared = yes; then
-  AC_DEFINE(GUILE_SIGWINCH_SA_RESTART_CLEARED, 1,
-    [Define if readline disables SA_RESTART.])
-fi
-
 AC_CACHE_CHECK([for rl_getc_function pointer in readline],
 		 ac_cv_var_rl_getc_function,
 		 [AC_TRY_LINK([
diff --git a/guile-readline/readline.c b/guile-readline/readline.c
index 84ae62260..7f86ceb3d 100644
--- a/guile-readline/readline.c
+++ b/guile-readline/readline.c
@@ -530,26 +530,6 @@ match_paren (int x, int k)
 }
 #endif /* HAVE_RL_GET_KEYMAP */
 
-#if defined (HAVE_RL_PRE_INPUT_HOOK) && defined (GUILE_SIGWINCH_SA_RESTART_CLEARED)
-/* Readline disables SA_RESTART on SIGWINCH.
- * This code turns it back on.
- */
-static int
-sigwinch_enable_restart (void)
-{
-#ifdef HAVE_SIGINTERRUPT
-  siginterrupt (SIGWINCH, 0);
-#else
-  struct sigaction action;
-  
-  sigaction (SIGWINCH, NULL, &action);
-  action.sa_flags |= SA_RESTART;
-  sigaction (SIGWINCH, &action, NULL);
-#endif
-  return 0;
-}
-#endif
-
 #endif /* HAVE_RL_GETC_FUNCTION */
 
 void
@@ -569,9 +549,6 @@ scm_init_readline ()
 #endif
   rl_basic_word_break_characters = "\t\n\"'`;()";
   rl_readline_name = "Guile";
-#if defined (HAVE_RL_PRE_INPUT_HOOK) && defined (GUILE_SIGWINCH_SA_RESTART_CLEARED)
-  rl_pre_input_hook = sigwinch_enable_restart;
-#endif
 
   reentry_barrier_mutex = scm_permanent_object (scm_make_mutex ());
   scm_init_opts (scm_readline_options,