Add new function _Exit().

* NEWS.11.md: Announce addition.

* bootstrap.conf: Add "_Exit" to list of gnulib modules to import.

* _Exit-wrapper.h (octave__Exit_wrapper), _Exit-wrapper.c: New files for
wrapper function which maps to gnulib _Exit.

* liboctave/wrappers/module.mk: Add new files to build system.

* syscalls.cc (F_Exit): New function which calls octave wrapper for gnulib
_Exit.
* syscalls.cc (Ffork): Improve documentation and explain use of _Exit().
Add seealso link to _Exit.

* octave-popen2.c: Change to use _Exit rather than _exit for consistency.

* system.txi: Add DOCSTRING to manual.

Author: Rik

bootstrap.conf

@@ -27,6 +27,7 @@
 
 # gnulib modules used by this package.
 gnulib_modules="
+  _Exit
   areadlink
   base64
   bison

doc/interpreter/system.txi

@@ -367,6 +367,8 @@ they can be used, look at the definition of the function @code{popen2}.
 
 @DOCSTRING(fork)
 
+@DOCSTRING(_Exit)
+
 @DOCSTRING(exec)
 
 @DOCSTRING(pipe)

etc/NEWS.11.md

@@ -29,6 +29,10 @@ Summary of important user-visible changes for version 11 (yyyy-mm-dd):
   or permutation of the inputs for performance.  Now Octave automatically picks
   the fastest calculation order irrespective of the input orientation.
 
+- New function `_Exit` has been added which makes it possible to use
+  `fork`/`_Exit` sequence to perform work in parallel child processes for
+  potential performance gains.
+
 - The `fzero` function is now more accurate (1-2 eps when TolX is eps).
 
 - The `roots` function now accepts only a numeric argument.  Convert any
@@ -111,6 +115,7 @@ Summary of important user-visible changes for version 11 (yyyy-mm-dd):
 
 ### Alphabetical list of new functions added in Octave 11
 
+* `_Exit`
 * `corrcov`
 
 ### Deprecated functions, properties, and operators

libinterp/corefcn/syscalls.cc

@@ -33,8 +33,10 @@
 #endif
 
 #include <cstdio>
+#include <cstdlib>
 #include <cstring>
 
+#include "_Exit-wrapper.h"
 #include "cmd-hist.h"
 #include "fcntl-wrappers.h"
 #include "file-ops.h"
@@ -496,17 +498,19 @@ Fork can return one of the following values:
 @table @asis
 @item > 0
 You are in the parent process.  The value returned from @code{fork} is the
-process id of the child process.  You should probably arrange to wait for
-any child processes to exit.
+process id of the child process.  You should probably arrange to wait for any
+child processes to exit by using @code{waitpid}.
 
 @item 0
 You are in the child process.  You can call @code{exec} to start another
-process.  If that fails, you should probably call @code{exit}.
+process.  If that fails, you should probably call @code{_Exit} to terminate the
+child.
 
 @item < 0
-The call to @code{fork} failed for some reason.  You must take evasive
-action.  A system dependent error message will be waiting in @var{msg}.
+The call to @code{fork} failed for some reason.  You must take evasive action.
+A system-dependent error message will be waiting in @var{msg}.
 @end table
+@seealso{exec, _Exit}
 @end deftypefn */)
 {
   if (args.length () != 0)
@@ -522,6 +526,35 @@ action.  A system dependent error message will be waiting in @var{msg}.
   return ovl (pid, msg);
 }
 
+DEFUNX ("_Exit", F_Exit, args, ,
+        doc: /* -*- texinfo -*-
+@deftypefn  {} {} _Exit ()
+@deftypefnx {} {} _Exit (@var{status})
+Exit the currently running process with exit code @var{status}.
+
+If called with no arguments, exit with status @code{0} indicating success.
+
+The optional integer argument @var{status} specifies the exit code.
+
+Programming Note: This function maps to the C++ function @code{quick_exit}.
+The calling process is stopped and any open file descriptors are closed.  This
+is the correct function to call to end a child process started from Octave.
+The ordinary C library function `exit` will not work.
+@seealso{fork}
+@end deftypefn */)
+{
+  int nargin = args.length ();
+  if (nargin > 1)
+    print_usage ();
+
+  int status = EXIT_SUCCESS;
+
+  if (nargin == 1)
+    status = args(0).xint_value ("_Exit: STATUS must be an integer");
+
+  octave__Exit_wrapper (status);
+}
+
 DEFUNX ("getpgrp", Fgetpgrp, args, ,
         doc: /* -*- texinfo -*-
 @deftypefn {} {pgid =} getpgrp ()

liboctave/wrappers/_Exit-wrapper.c

@@ -0,0 +1,42 @@
+////////////////////////////////////////////////////////////////////////
+//
+// Copyright (C) 2025 The Octave Project Developers
+//
+// See the file COPYRIGHT.md in the top-level directory of this
+// distribution or <https://octave.org/copyright/>.
+//
+// This file is part of Octave.
+//
+// Octave is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Octave is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Octave; see the file COPYING.  If not, see
+// <https://www.gnu.org/licenses/>.
+//
+////////////////////////////////////////////////////////////////////////
+
+// _Exit is provided by gnulib.  We don't include gnulib headers
+// directly in Octave's C++ source files to avoid problems that may be
+// caused by the way that gnulib overrides standard library functions.
+
+#if defined (HAVE_CONFIG_H)
+#  include "config.h"
+#endif
+
+#include "stdlib.h"
+
+#include "_Exit-wrapper.h"
+
+void
+octave__Exit_wrapper (int status)
+{
+  _Exit (status);
+}

liboctave/wrappers/_Exit-wrapper.h

@@ -0,0 +1,40 @@
+////////////////////////////////////////////////////////////////////////
+//
+// Copyright (C) 2025 The Octave Project Developers
+//
+// See the file COPYRIGHT.md in the top-level directory of this
+// distribution or <https://octave.org/copyright/>.
+//
+// This file is part of Octave.
+//
+// Octave is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Octave is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Octave; see the file COPYING.  If not, see
+// <https://www.gnu.org/licenses/>.
+//
+////////////////////////////////////////////////////////////////////////
+
+#if ! defined (octave__Exit_wrapper_h)
+#define octave__Exit_wrapper_h 1
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
+extern OCTAVE_API void 
+octave__Exit_wrapper (int status);
+
+#if defined (__cplusplus)
+}
+#endif
+
+#endif

liboctave/wrappers/module.mk

@@ -1,4 +1,5 @@
 NOINSTALL_WRAPPERS_INC = \
+  %reldir%/_Exit-wrapper.h \
   %reldir%/areadlink-wrapper.h \
   %reldir%/async-system-wrapper.h \
   %reldir%/base64-wrappers.h \
@@ -44,6 +45,7 @@ NOINSTALL_WRAPPERS_INC = \
   %reldir%/wait-wrappers.h
 
 WRAPPERS_SRC = \
+  %reldir%/_Exit-wrapper.c \
   %reldir%/areadlink-wrapper.c \
   %reldir%/async-system-wrapper.c \
   %reldir%/base64-wrappers.c \

liboctave/wrappers/octave-popen2.c

@@ -232,7 +232,7 @@ octave_popen2 (const char *cmd, char *const *args, bool sync_mode,
       else
         perror ("error: popen2 (child)");
 
-      _exit (OCTAVE_CHILD_FAILURE);  
+      _Exit (OCTAVE_CHILD_FAILURE);  
     }
   else if (pid > 0)
     {