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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
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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,