Re: [autoconf] AmigaOS fork()

[Rüdiger Kuhlmann]

>--[Akim Demaille]--<address@hidden>

> I'll wait for some input from Alexandre, Jim or Paul on this one.

> | >--[Tim Van Holder]--<address@hidden>

> | Okay, what about this: It doesn't #define fork anymore, but HAVE_FORK if it
> | works. Then the program has to check this itself.
> I prefer HAVE_WORKING_FORK.  Let's have HAVE_FOO keep its semantics.

Okay.

> We need some documentation, please.

Okay. Tell me if this is enough.

> | +#ifndef HAVE_FORK
> We avoid ifdef and ifndef, rather use
> #if !HAVE_FORK

Okay.

> AC_TRY_RUN is dead as far as Autoconf per se is concerned, please use
> AC_RUN_IFELSE.  See AC_FUNC_GETPGRP for instance.

Okay.

> | +        #if HAVE_UNISTD_H
> | +        # include <unistd.h>
> | +        #endif
> Hm, make sure you have the proper requirements to have this header
> test.  Maybe it's already the case via AC_CHECK_FUNC, but I doubt it.

Okay.

> | +          if (fork() < 0)
> | +            exit (1);

> No way to actually *test* the feature?

There _is_ a test. Look carefully. If fork() "always" fails,
it is a stub. If the fork() succeeds, it is not.

> Nit picking: two \n between defs.

Okay.

> | +  AC_DEFINE(HAVE_VFORK, 1, [Define if `vfork' works.])
> Again, HAVE_WORKING_VFORK seems more appropriate to me.

Okay.

> |  AC_DEFUN([AC_FUNC_WAIT3],
> | -[AC_CACHE_CHECK(for wait3 that fills in rusage, ac_cv_func_wait3_rusage,
> | +[AC_REQUIRE([AC_FUNC_FORK])dnl
> | +AC_CACHE_CHECK(for wait3 that fills in rusage, ac_cv_func_wait3_rusage,
> | [...]
> | +#ifndef HAVE_FORK
> | +# define fork vfork
> | +#endif

> Instead of ``polluting'' all the tests, I'd suggest inserting this
> snippet in confdefs.h.  But I'd like to hear comments about this.

No. This would be wrong. Then I'd better #define fork to be vfork. But vfork
is not necessarily a replacement for fork. But for the tests at hand, it is.

Another idea would be to add

#if HAVE_WORKING_FORK
#define forkvfork fork
#else
#if HAVE_WORKING_VFORK
#define forkvfork vfork
#else
#error Neither fork nor vfork available.
#endif
#endif

to confdefs.h and replace fork by forkvfork where appropriate.  forkvfork in
the sense of prefer fork, but replace by vfork. Comments about that?

2001-05-31 Rüdiger Kuhlmann <address@hidden>

        * acfunctions.m4: (AC_FUNC_FORK) New, check whether fork() isn't just
          a stub and define HAVE_WORKING_FUNC if it works.
          (AC_FUNC_GETPGRP, AC_FUNC_WAIT3) Use AC_FUNC_FORK and #define fork
          to vfork if necessary.
          (AC_FUN_VFORK) Similarly define HAVE_WORKING_VFORK.
        * acspecific.m4: (AC_SYS_RESTARTABLE_SYSCALLS) dito.
        * acfunctions: add HAVE_FORK.
        * doc/autoconf.texi: Document AC_FUNC_FORK.

Index: acfunctions
===================================================================
RCS file: /cvs/autoconf/acfunctions,v
retrieving revision 1.13
diff -u -r1.13 acfunctions
--- acfunctions 2001/01/24 07:58:59     1.13
+++ acfunctions 2001/05/31 13:12:28
@@ -7,6 +7,7 @@
 error          AC_FUNC_ERROR_AT_LINE
 error_at_line  AC_FUNC_ERROR_AT_LINE
 fnmatch                AC_FUNC_FNMATCH
+fork           AC_FUNC_FORK     
 fseeko         AC_FUNC_FSEEKO
 ftello         AC_FUNC_FSEEKO
 getgroups      AC_FUNC_GETGROUPS
Index: acfunctions.m4
===================================================================
RCS file: /cvs/autoconf/acfunctions.m4,v
retrieving revision 1.33
diff -u -r1.33 acfunctions.m4
--- acfunctions.m4      2001/04/22 12:50:07     1.33
+++ acfunctions.m4      2001/05/31 13:12:31
@@ -599,7 +599,8 @@
 # AC_FUNC_GETPGRP
 # ---------------
 AC_DEFUN([AC_FUNC_GETPGRP],
-[AC_CACHE_CHECK(whether getpgrp takes no argument, ac_cv_func_getpgrp_void,
+[AC_REQUIRE([AC_FUNC_FORK])dnl
+AC_CACHE_CHECK(whether getpgrp takes no argument, ac_cv_func_getpgrp_void,
 [AC_RUN_IFELSE([AC_LANG_SOURCE([[
 /*
  * If this system has a BSD-style getpgrp(),
@@ -609,6 +610,9 @@
  */
 #include <stdio.h>
 #include <sys/types.h>
+#if !HAVE_WORKING_FORK
+# define fork vfork
+#endif
 
 int     pid;
 int     pg1, pg2, pg3, pg4;
@@ -1442,6 +1446,42 @@
 AU_ALIAS([AC_UTIME_NULL], [AC_FUNC_UTIME_NULL])
 
 
+# AC_FUNC_FORK
+# -------------
+AC_DEFUN([AC_FUNC_FORK],
+  [AC_CHECK_FUNC(fork)
+  ac_cv_func_fork_works=$ac_cv_func_fork
+  if test "x$ac_cv_func_fork" = xyes; then
+    AC_CACHE_CHECK(for working fork, ac_cv_func_fork_works,
+      [AC_CHECK_HEADERS(unistd.h)
+      AC_RUN_IFELSE([/* By Rüdiger Kuhlmann. */
+        #include <sys/types.h>
+        #if HAVE_UNISTD_H
+        # include <unistd.h>
+        #endif
+        /* Some systems only have a dummy stub for fork() */
+        int main ()
+        {
+          if (fork() < 0)
+            exit (1);
+          exit (0);
+        }],
+      [ac_cv_func_fork_works=yes],
+      [ac_cv_func_fork_works=no],
+      [dnl
+        case "$host" in
+          *-*-amigaos* | *-*-msdosdjgpp*)
+            # Override, as these systems have only a dummy fork() stub
+            ac_cv_func_fork_works=no
+            ;;
+        esac])])
+  fi
+  if test "x$ac_cv_func_fork_works" = xyes; then
+    AC_DEFINE(HAVE_WORKING_FORK,1)
+  endif
+])# AC_FUNC_FORK
+
+
 # AC_FUNC_VFORK
 # -------------
 AC_DEFUN([AC_FUNC_VFORK],
@@ -1547,6 +1587,8 @@
 ac_cv_func_vfork_works=$ac_cv_func_vfork])])
 if test "x$ac_cv_func_vfork_works" = xno; then
   AC_DEFINE(vfork, fork, [Define as `fork' if `vfork' does not work.])
+else
+  AC_DEFINE(HAVE_WORKING_VFORK, 1, [Define if `vfork' works.])
 fi
 ])# AC_FUNC_VFORK
 
@@ -1577,12 +1619,16 @@
 # AC_FUNC_WAIT3
 # -------------
 AC_DEFUN([AC_FUNC_WAIT3],
-[AC_CACHE_CHECK(for wait3 that fills in rusage, ac_cv_func_wait3_rusage,
+[AC_REQUIRE([AC_FUNC_FORK])dnl
+AC_CACHE_CHECK(for wait3 that fills in rusage, ac_cv_func_wait3_rusage,
 [AC_TRY_RUN(
 [#include <sys/types.h>
 #include <sys/time.h>
 #include <sys/resource.h>
 #include <stdio.h>
+#if !HAVE_WORKING_FORK
+# define fork vfork
+#endif
 /* HP-UX has wait3 but does not fill in rusage at all.  */
 int
 main ()
Index: acspecific.m4
===================================================================
RCS file: /cvs/autoconf/acspecific.m4,v
retrieving revision 1.338
diff -u -r1.338 acspecific.m4
--- acspecific.m4       2001/04/15 16:20:30     1.338
+++ acspecific.m4       2001/05/31 13:12:35
@@ -495,6 +495,7 @@
 # interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'.
 AC_DEFUN([AC_SYS_RESTARTABLE_SYSCALLS],
 [AC_REQUIRE([AC_HEADER_SYS_WAIT])dnl
+AC_REQUIRE([AC_FUNC_FORK])dnl
 AC_CHECK_HEADERS(unistd.h)
 AC_CACHE_CHECK(for restartable system calls, ac_cv_sys_restartable_syscalls,
 [AC_RUN_IFELSE([AC_LANG_SOURCE(
@@ -509,6 +510,9 @@
 #endif
 #if HAVE_SYS_WAIT_H
 # include <sys/wait.h>
+#endif
+#if !HAVE_WORKING_FORK
+# define fork vfork
 #endif
 
 /* Some platforms explicitly require an extern "C" signal handler
Index: doc/autoconf.texi
===================================================================
RCS file: /cvs/autoconf/doc/autoconf.texi,v
retrieving revision 1.452
diff -u -r1.452 autoconf.texi
--- doc/autoconf.texi   2001/05/31 07:32:27     1.452
+++ doc/autoconf.texi   2001/05/31 13:13:04
@@ -3226,6 +3226,13 @@
 SunOS 5.4), define @code{HAVE_FNMATCH}.
 @end defmac
 
address@hidden AC_FUNC_FORK
address@hidden FUNC_FORK
address@hidden HAVE_WORKING_FORK
+If a working @code{fork} is not found, define @code{HAVE_WORKING_FORK}. This
+macro only checks whether @code{fork} ist just a stub.
address@hidden defmac
+
 @defmac AC_FUNC_FSEEKO
 @maindex FUNC_FSEEKO
 @cvindex _LARGEFILE_SOURCE
@@ -3459,14 +3466,16 @@
 @defmac AC_FUNC_VFORK
 @maindex FUNC_VFORK
 @cvindex HAVE_VFORK_H
address@hidden HAVE_WORKING_VFORK
 @cvindex vfork
 If @file{vfork.h} is found, define @code{HAVE_VFORK_H}.  If a working
address@hidden is not found, define @code{vfork} to be @code{fork}.  This
-macro checks for several known errors in implementations of @code{vfork}
-and considers the system to not have a working @code{vfork} if it
-detects any of them.  It is not considered to be an implementation error
-if a child's invocation of @code{signal} modifies the parent's signal
-handler, since child processes rarely change their signal handlers.
address@hidden is not found, define @code{vfork} to be @code{fork},
+and define @code{HAVE_WORKING_VFORK}.  This macro checks for several known
+errors in implementations of @code{vfork} and considers the system to not
+have a working @code{vfork} if it detects any of them.  It is not considered
+to be an implementation error if a child's invocation of @code{signal}
+modifies the parent's signal handler, since child processes rarely change
+their signal handlers.
 @end defmac
 
 @defmac AC_FUNC_VPRINTF


Yours, Rüdiger.

-- 
A "No" uttered from deepest conviction is better and greater than a
"Yes" merely uttered to please, or what is worse, to avoid trouble.
                -- Mahatma Ghandi