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Remove AC_SYS_RESTARTABLE_SYSCALLS and related code

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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:
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.

* 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.
This commit is contained in:
Neil Jerram 2009-06-18 20:35:45 +01:00
parent d2cb6b102b
commit 5e9dc714ca
6 changed files with 2 additions and 158 deletions
Download patch file Download diff file Expand all files Collapse all files

71
guile-readline/configure.in
View file

@ -53,77 +53,6 @@ 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([

23
guile-readline/readline.c
View file

@ -531,26 +531,6 @@ 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
@ -570,9 +550,6 @@ 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,