threadsafe: Load preferences threadsafe

Instead of static variables in a function, we store preferences in a
struct and use an `atomic_int` to prevent any more than one thread from
loading preferences.

Fixes #440

Signed-off-by: Johannes Demel <[email protected]>

Author: jdemel

include/volk/volk_prefs.h

@@ -13,6 +13,12 @@ typedef struct volk_arch_pref {
     char impl_u[128]; // best unaligned impl
 } volk_arch_pref_t;
 
+
+VOLK_API void volk_initialize_preferences();
+VOLK_API void volk_free_preferences();
+VOLK_API const size_t volk_get_num_arch_prefs();
+VOLK_API const volk_arch_pref_t* volk_get_arch_prefs();
+
 ////////////////////////////////////////////////////////////////////////
 // get path to volk_config profiling info; second arguments specifies
 // if config file should be tested on existence for reading.

lib/volk_prefs.c

@@ -10,6 +10,7 @@
 #include <unistd.h>
 #endif
 #include <volk/volk_prefs.h>
+#include <stdatomic.h>
 
 void volk_get_config_path(char* path, bool read)
 {
@@ -63,6 +64,48 @@ void volk_get_config_path(char* path, bool read)
     return;
 }
 
+
+static struct volk_preferences {
+    volk_arch_pref_t* volk_arch_prefs;
+    size_t n_arch_prefs;
+    atomic_int initialized;
+    
+} volk_preferences;
+
+
+void volk_initialize_preferences()
+{
+    if (!atomic_fetch_and(&volk_preferences.initialized, 1)) {
+        volk_preferences.n_arch_prefs =
+            volk_load_preferences(&volk_preferences.volk_arch_prefs);
+    }
+}
+
+
+void volk_free_preferences()
+{
+    if (volk_preferences.initialized) {
+        free(volk_preferences.volk_arch_prefs);
+        volk_preferences.n_arch_prefs = 0;
+        volk_preferences.initialized = 0;
+    }
+}
+
+
+const size_t volk_get_num_arch_prefs()
+{
+    volk_initialize_preferences();
+    return volk_preferences.n_arch_prefs;
+}
+
+
+const volk_arch_pref_t* volk_get_arch_prefs()
+{
+    volk_initialize_preferences();
+    return volk_preferences.volk_arch_prefs;
+}
+
+
 size_t volk_load_preferences(volk_arch_pref_t** prefs_res)
 {
     FILE* config_file;

lib/volk_rank_archs.c

@@ -53,13 +53,9 @@ int volk_rank_archs(const char* kern_name,    // name of the kernel to rank
 )
 {
     size_t i;
-    static volk_arch_pref_t* volk_arch_prefs;
-    static size_t n_arch_prefs = 0;
-    static int prefs_loaded = 0;
-    if (!prefs_loaded) {
-        n_arch_prefs = volk_load_preferences(&volk_arch_prefs);
-        prefs_loaded = 1;
-    }
+
+    const volk_arch_pref_t* volk_arch_prefs = volk_get_arch_prefs();
+    const size_t n_arch_prefs = volk_get_num_arch_prefs();
 
     // If we've defined VOLK_GENERIC to be anything, always return the
     // 'generic' kernel. Used in GR's QA code.