Make the configure script check whether the FFTW library that was found is a threaded build or not.

configure.ac

@@ -589,6 +589,7 @@ AH_VERBATIM([__STDC_FORMAT_MACROS],
 # Check for FFTW. We test for this in the standard directories by default,
 # and only disable if using --with-fftw=no or --without-fftw. When a value
 # is given FFTW must be found.
+# If FFTW is found, we check whether this is the threaded version.
 have_fftw="no"
 AC_ARG_WITH([fftw],
     [AS_HELP_STRING([--with-fftw=PATH],
@@ -598,29 +599,60 @@ AC_ARG_WITH([fftw],
     [with_fftw="test"]
 )
 if test "x$with_fftw" != "xno"; then
+
+   # Was FFTW's location specifically given?
    if test "x$with_fftw" != "xyes" -a "x$with_fftw" != "xtest" -a "x$with_fftw" != "x"; then
-      FFTW_LIBS="-L$with_fftw/lib -lfftw3_threads -lfftw3"
+      FFTW_LIBS="-L$with_fftw/lib -lfftw3"
       FFTW_INCS="-I$with_fftw/include"
    else
-      FFTW_LIBS="-lfftw3_threads -lfftw3"
+      FFTW_LIBS="-lfftw3"
       FFTW_INCS=""
    fi
+
    #  FFTW is not specified, so just check if we have it.
    if test "x$with_fftw" = "xtest"; then
       AC_CHECK_LIB([fftw3],[fftw_malloc],[have_fftw="yes"],[have_fftw="no"],$FFTW_LIBS)
       if test "x$have_fftw" != "xno"; then
       	 AC_DEFINE([HAVE_FFTW],1,[The FFTW library appears to be present.])
       fi
+   # FFTW was specified, check that it was a valid location.
    else
       AC_CHECK_LIB([fftw3],[fftw_malloc],
          AC_DEFINE([HAVE_FFTW],1,[The FFTW library appears to be present.]),
          AC_MSG_ERROR(something is wrong with the FFTW library!), $FFTW_LIBS)
       have_fftw="yes"
    fi
+
+   # FFTW was requested not to be used.
    if test "$have_fftw" = "no"; then
       FFTW_LIBS=""
       FFTW_INCS=""
    fi
+
+   # Now, check whether we have the threaded version of FFTW
+   if test "x$have_fftw" = "xyes"; then
+
+      # Was FFTW's location specifically given?
+      if test "x$with_fftw" != "xyes" -a "x$with_fftw" != "xtest" -a "x$with_fftw" != "x"; then
+        FFTW_THREADED_LIBS="-L$with_fftw/lib -lfftw3_threads -lfftw3"
+        FFTW_THREADED_INCS="-I$with_fftw/include"
+      else
+        FFTW_THREADED_LIBS="-lfftw3_threads -lfftw3"
+        FFTW_THREADED_INCS=""
+      fi
+
+      # Verify that the library is threaded
+      AC_CHECK_LIB([fftw3],[fftw_init_threads],[have_threaded_fftw="yes"],
+		   [have_threaded_fftw="no"], $FFTW_THREADED_LIBS)
+
+      # If found, update things
+      if test "x$have_threaded_fftw" = "xyes"; then
+         AC_DEFINE([HAVE_THREADED_FFTW],1,[The threaded FFTW library appears to be present.])
+         FFTW_LIBS=$FFTW_THREADED_LIBS
+         FFTW_INCS=$FFTW_THREADED_INCS
+	 have_fftw="yes - threaded"
+      fi
+   fi
 fi
 AC_SUBST([FFTW_LIBS])
 AC_SUBST([FFTW_INCS])

src/mesh_gravity.c

@@ -624,11 +624,13 @@ void pm_mesh_init(struct pm_mesh* mesh, const struct gravity_props* props,
   if (2. * mesh->r_cut_max > box_size)
     error("Mesh too small or r_cut_max too big for this box size");
 
+#ifdef HAVE_THREADED_FFTW
   /* Initialise the thread-parallel FFTW version */
   if (N >= 64) {
     fftw_init_threads();
     fftw_plan_with_nthreads(nr_threads);
   }
+#endif
 
   /* Allocate the memory for the combined density and potential array */
   mesh->potential = (double*)fftw_malloc(sizeof(double) * N * N * N);
@@ -668,7 +670,9 @@ void pm_mesh_init_no_mesh(struct pm_mesh* mesh, double dim[3]) {
  */
 void pm_mesh_clean(struct pm_mesh* mesh) {
 
+#ifdef HAVE_THREADED_FFTW
   fftw_cleanup_threads();
+#endif
 
   if (mesh->potential) free(mesh->potential);
   mesh->potential = 0;
@@ -702,11 +706,13 @@ void pm_mesh_struct_restore(struct pm_mesh* mesh, FILE* stream) {
 #ifdef HAVE_FFTW
     const int N = mesh->N;
 
+#ifdef HAVE_THREADED_FFTW
     /* Initialise the thread-parallel FFTW version */
     if (N >= 64) {
       fftw_init_threads();
       fftw_plan_with_nthreads(mesh->nr_threads);
     }
+#endif
 
     /* Allocate the memory for the combined density and potential array */
     mesh->potential = (double*)fftw_malloc(sizeof(double) * N * N * N);