implement --enable-threads and a thread-less mode

configure.ac

@@ -237,6 +237,7 @@ OPTION_DEFAULT_ON([gsettings],[don't compile with GSettings support])
 OPTION_DEFAULT_ON([selinux],[don't compile with SELinux support])
 OPTION_DEFAULT_ON([gnutls],[don't use -lgnutls for SSL/TLS support])
 OPTION_DEFAULT_ON([zlib],[don't compile with zlib decompression support])
+OPTION_DEFAULT_ON([threads],[don't compile with elisp threading support])
 
 AC_ARG_WITH([file-notification],[AS_HELP_STRING([--with-file-notification=LIB],
  [use a file notification library (LIB one of: yes, gfile, inotify, w32, no)])],
@@ -1948,6 +1949,17 @@ AC_SUBST([LIB_PTHREAD])
 
 AC_CHECK_LIB(pthreads, cma_open)
 
+AC_MSG_CHECKING([for thread support])
+threads_enabled=no
+if test "$with_threads" = yes; then
+   if test "$HAVE_PTHREAD" = yes; then
+      AC_DEFINE(THREADS_ENABLED, 1,
+                [Define to 1 if you want elisp thread support.])
+      threads_enabled=yes
+   fi
+fi
+AC_MSG_RESULT([$threads_enabled])
+
 ## Note: when using cpp in s/aix4.2.h, this definition depended on
 ## HAVE_LIBPTHREADS.  That was not defined earlier in configure when
 ## the system file was sourced.  Hence the value of LIBS_SYSTEM
@@ -4843,6 +4855,7 @@ echo "  Does Emacs use -lxft?                                   ${HAVE_XFT}"
 echo "  Does Emacs directly use zlib?                           ${HAVE_ZLIB}"
 
 echo "  Does Emacs use toolkit scroll bars?                     ${USE_TOOLKIT_SCROLL_BARS}"
+echo "  Does Emacs have threading support in elisp?             ${threads_enabled}"
 echo
 
 if test -n "${EMACSDATA}"; then

src/systhread.c

@@ -1,5 +1,5 @@
 /* System thread definitions
-   Copyright (C) 2012 Free Software Foundation, Inc.
+   Copyright (C) 2012, 2013 Free Software Foundation, Inc.
 
 This file is part of GNU Emacs.
 
@@ -20,7 +20,80 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <setjmp.h>
 #include "lisp.h"
 
-#ifdef HAVE_PTHREAD
+#ifndef THREADS_ENABLED
+
+void
+sys_mutex_init (sys_mutex_t *m)
+{
+  *m = 0;
+}
+
+void
+sys_mutex_lock (sys_mutex_t *m)
+{
+}
+
+void
+sys_mutex_unlock (sys_mutex_t *m)
+{
+}
+
+void
+sys_mutex_destroy (sys_mutex_t *m)
+{
+}
+
+void
+sys_cond_init (sys_cond_t *c)
+{
+  *c = 0;
+}
+
+void
+sys_cond_wait (sys_cond_t *c, sys_mutex_t *m)
+{
+}
+
+void
+sys_cond_signal (sys_cond_t *c)
+{
+}
+
+void
+sys_cond_broadcast (sys_cond_t *c)
+{
+}
+
+void
+sys_cond_destroy (sys_cond_t *c)
+{
+}
+
+sys_thread_t
+sys_thread_self (void)
+{
+  return 0;
+}
+
+int
+sys_thread_equal (sys_thread_t x, sys_thread_t y)
+{
+  return x == y;
+}
+
+int
+sys_thread_create (sys_thread_t *t, const char *name,
+		   thread_creation_function *func, void *datum)
+{
+  return 0;
+}
+
+void
+sys_thread_yield (void)
+{
+}
+
+#elif defined (HAVE_PTHREAD)
 
 #include <sched.h>
 

src/systhread.h

@@ -1,5 +1,5 @@
 /* System thread definitions
-   Copyright (C) 2012 Free Software Foundation, Inc.
+   Copyright (C) 2012, 2013 Free Software Foundation, Inc.
 
 This file is part of GNU Emacs.
 
@@ -19,6 +19,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef SYSTHREAD_H
 #define SYSTHREAD_H
 
+#ifdef THREADS_ENABLED
+
 #ifdef HAVE_PTHREAD
 
 #include <pthread.h>
@@ -32,11 +34,20 @@ typedef pthread_cond_t sys_cond_t;
 /* A system thread.  */
 typedef pthread_t sys_thread_t;
 
-#else
+#else /* HAVE_PTHREAD */
 
 #error port me
 
-#endif
+#endif /* HAVE_PTHREAD */
+
+#else /* THREADS_ENABLED */
+
+/* For the no-threads case we can simply use dummy definitions.  */
+typedef int sys_mutex_t;
+typedef int sys_cond_t;
+typedef int sys_thread_t;
+
+#endif /* THREADS_ENABLED */
 
 typedef void *(thread_creation_function) (void *);
 

src/thread.c

@@ -937,24 +937,29 @@ init_threads (void)
 void
 syms_of_threads (void)
 {
-  defsubr (&Sthread_yield);
-  defsubr (&Smake_thread);
-  defsubr (&Scurrent_thread);
-  defsubr (&Sthread_name);
-  defsubr (&Sthread_signal);
-  defsubr (&Sthread_alive_p);
-  defsubr (&Sthread_join);
-  defsubr (&Sthread_blocker);
-  defsubr (&Sall_threads);
-  defsubr (&Smake_mutex);
-  defsubr (&Smutex_lock);
-  defsubr (&Smutex_unlock);
-  defsubr (&Smutex_name);
-  defsubr (&Smake_condition_variable);
-  defsubr (&Scondition_wait);
-  defsubr (&Scondition_notify);
-  defsubr (&Scondition_mutex);
-  defsubr (&Scondition_name);
+#ifndef THREADS_ENABLED
+  if (0)
+#endif
+    {
+      defsubr (&Sthread_yield);
+      defsubr (&Smake_thread);
+      defsubr (&Scurrent_thread);
+      defsubr (&Sthread_name);
+      defsubr (&Sthread_signal);
+      defsubr (&Sthread_alive_p);
+      defsubr (&Sthread_join);
+      defsubr (&Sthread_blocker);
+      defsubr (&Sall_threads);
+      defsubr (&Smake_mutex);
+      defsubr (&Smutex_lock);
+      defsubr (&Smutex_unlock);
+      defsubr (&Smutex_name);
+      defsubr (&Smake_condition_variable);
+      defsubr (&Scondition_wait);
+      defsubr (&Scondition_notify);
+      defsubr (&Scondition_mutex);
+      defsubr (&Scondition_name);
+    }
 
   Qthreadp = intern_c_string ("threadp");
   staticpro (&Qthreadp);