Be more verbose about using homemeade barriers.

configure.ac

@@ -380,9 +380,13 @@ AX_PTHREAD([LIBS="$PTHREAD_LIBS $LIBS" CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
     non-standard location.]))
 
 # Check whether POSIX thread barriers are implemented (e.g. OSX does not have them)
+have_pthread_barrier="no"
 AC_CHECK_LIB(pthread, pthread_barrier_init,
-	     AC_DEFINE([HAVE_PTHREAD_BARRIERS], [1], [The posix library implements barriers]),
+	     have_pthread_barrier="yes",
 	     AC_MSG_WARN(POSIX implementation does not have barriers. SWIFT will use home-made ones.))
+if test "x$have_pthread_barrier" == "xyes"; then
+  AC_DEFINE([HAVE_PTHREAD_BARRIERS], [1], [The posix library implements barriers])
+fi
 
 # Check whether POSIX file allocation functions exist (e.g. OSX does not have them)
 AC_CHECK_LIB(pthread, posix_fallocate,
@@ -914,19 +918,20 @@ AC_MSG_RESULT([
 
    $PACKAGE_NAME v.$PACKAGE_VERSION
 
-   Compiler        : $CC
-    - vendor       : $ax_cv_c_compiler_vendor
-    - version      : $ax_cv_c_compiler_version
-    - flags        : $CFLAGS
-   MPI enabled     : $enable_mpi
-   HDF5 enabled    : $with_hdf5
-    - parallel     : $have_parallel_hdf5
-   Metis enabled   : $have_metis
-   FFTW3 enabled   : $have_fftw3
-   libNUMA enabled : $have_numa
-   Using tcmalloc  : $have_tcmalloc
-   Using jemalloc  : $have_jemalloc
-   CPU profiler    : $have_profiler
+   Compiler         : $CC
+    - vendor        : $ax_cv_c_compiler_vendor
+    - version       : $ax_cv_c_compiler_version
+    - flags         : $CFLAGS
+   MPI enabled      : $enable_mpi
+   HDF5 enabled     : $with_hdf5
+    - parallel      : $have_parallel_hdf5
+   Metis enabled    : $have_metis
+   FFTW3 enabled    : $have_fftw3
+   libNUMA enabled  : $have_numa
+   Using tcmalloc   : $have_tcmalloc
+   Using jemalloc   : $have_jemalloc
+   CPU profiler     : $have_profiler
+   Pthread barriers : $have_pthread_barrier
 
    Hydro scheme       : $with_hydro
    Dimensionality     : $with_dimension

examples/main.c

@@ -390,6 +390,13 @@ int main(int argc, char *argv[]) {
       message("WARNING: Floating point exceptions will be reported.");
   }
 
+/* Do we have slow barriers? */
+#ifdef HAVE_PTHREAD_BARRIERS
+  if (myrank == 0)
+    message(
+        "WARNING: Slow homemade thread barriers in use. Code will be slower.");
+#endif
+
   /* How large are the parts? */
   if (myrank == 0) {
     message("sizeof(part)        is %4zi bytes.", sizeof(struct part));

src/common_io.c

@@ -386,6 +386,7 @@ void io_write_code_description(hid_t h_file) {
                        configuration_options());
   io_write_attribute_s(h_grpcode, "CFLAGS", compilation_cflags());
   io_write_attribute_s(h_grpcode, "HDF5 library version", hdf5_version());
+  io_write_attribute_s(h_grpcode, "Thread barriers", thread_barrier_version());
 #ifdef HAVE_FFTW
   io_write_attribute_s(h_grpcode, "FFTW library version", fftw3_version());
 #endif

src/version.c

@@ -332,6 +332,22 @@ const char *fftw3_version(void) {
   return version;
 }
 
+/**
+ * @brief return the thread barrier used in SWIFT.
+ *
+ * @result description of the thread barriers
+ */
+const char *thread_barrier_version(void) {
+
+  static char version[256] = {0};
+#if defined(HAVE_PTHREAD_BARRIERS)
+  sprintf(version, "%s", "pthread");
+#else
+  sprintf(version, "homemade");
+#endif
+  return version;
+}
+
 /**
  * @brief Prints a greeting message to the standard output containing code
  * version and revision number

src/version.h

@@ -34,6 +34,7 @@ const char* mpi_version(void);
 const char* metis_version(void);
 const char* hdf5_version(void);
 const char* fftw3_version(void);
+const char* thread_barrier_version(void);
 void greetings(void);
 
 #endif /* SWIFT_VERSION_H */