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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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14
libguile/_scm.h
View file

@ -78,20 +78,6 @@
#include "libguile/modules.h"
#include "libguile/inline.h"
/* SCM_SYSCALL retries system calls that have been interrupted (EINTR).
However this can be avoided if the operating system can restart
system calls automatically. We assume this is the case if
sigaction is available and SA_RESTART is defined; they will be used
when installing signal handlers.
*/
#ifdef HAVE_RESTARTABLE_SYSCALLS
#if ! SCM_USE_PTHREAD_THREADS /* However, don't assume SA_RESTART
works with pthreads... */
#define SCM_SYSCALL(line) line
#endif
#endif
#ifndef SCM_SYSCALL
#ifdef vms
# ifndef __GNUC__