Re: AC_SYS_RESTARTABLE_SYSCALLS

[Paul Eggert]

Ian Lance Taylor <address@hidden> writes:

> I couldn't think of any dynamic test which ran quickly.  Note that the
> autoconf test takes a few seconds.

Here's an idea.  Create a pipe, but close the read side.  Let the
write side be file descriptor W.  Write to W.  This will give you a
SIGPIPE signal.  In the SIGPIPE handler, use dup2 to cause W to point
to /dev/null instead of to the pipe's write side.  If system calls are
restarted, the write will succeed; if not, it'll fail with errno set
to SIGINT.


> How about something like this:

Thanks.  I added a few more details and installed the following:

2003-09-07  Paul Eggert  <address@hidden>

        * lib/autoconf/specific.m4 (AC_SYS_RESTARTABLE_SYSCALLS):
        Improve the accuracy of the wording about obsolescence.
        From a suggestion by Ian Lance Taylor in
        <http://mail.gnu.org/archive/html/autoconf/2003-09/msg00044.html>.

Index: specific.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/autoconf/specific.m4,v
retrieving revision 1.355
retrieving revision 1.356
diff -p -u -r1.355 -r1.356
--- specific.m4 22 May 2003 13:24:07 -0000      1.355
+++ specific.m4 8 Sep 2003 00:55:50 -0000       1.356
@@ -252,9 +252,10 @@ fi
 # interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'.
 AC_DEFUN([AC_SYS_RESTARTABLE_SYSCALLS],
 [AC_DIAGNOSE([obsolete],
-[$0: System call restartability is now typically set at runtime.
-Remove this `AC_SYS_RESTARTABLE_SYSCALLS'
-and adjust your code to use `sigaction' with `SA_RESTART' instead.])dnl
+[$0: AC_SYS_RESTARTABLE_SYSCALLS is useful only when supporting very
+old systems that lack `sigaction' and `SA_RESTART'.  Don't bother with
+this macro unless you need to support very old systems like 4.2BSD and
+SVR3.])dnl
 AC_REQUIRE([AC_HEADER_SYS_WAIT])dnl
 AC_CHECK_HEADERS(unistd.h)
 AC_CACHE_CHECK(for restartable system calls, ac_cv_sys_restartable_syscalls,