add duplicate init detection

.gitignore

@@ -2,6 +2,7 @@
 # Prerequisites
 *.d
 
+.cache
 compile_commands.json
 
 # Object files

inc/topo.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <stdio.h>
+#include <stdint.h>
 
 #ifdef __cplusplus 
 extern "C" {

test/test.c

@@ -96,6 +96,7 @@ int ts_test()
 int main()
 {
     topo_init(1, 1);
+    topo_init(1, 0);
     ts_test();
     return 0;
 }

topo.c

@@ -8,6 +8,7 @@
 #include <sys/_cpuset.h>
 #include <sys/cpuset.h>
 #include <sys/sysctl.h>
+#include <stdatomic.h>
 
 
 #include "libxml/parser.h"
@@ -413,6 +414,9 @@ topo_core_to_numa(int coreid)
     return _topo_core_to_numa(g_tobj, coreid);
 }
 
+static _Atomic(int) initialized = 0;
+static volatile int init_rc = 0;
+
 void
 topo_destroy()
 {
@@ -422,5 +426,15 @@ topo_destroy()
 int
 topo_init(int verbose, int alloc_init)
 {
-    return _topo_init(verbose, alloc_init, &g_tobj);
+    int expected = 0;
+    if (atomic_compare_exchange_strong(&initialized, &expected, 2)) {
+        init_rc = _topo_init(verbose, alloc_init, &g_tobj);
+        atomic_store(&initialized, 1);
+    } else {
+        while(atomic_load(&initialized) != 1) {} // wait for init
+        if (verbose) {
+            fprintf(stdout, "libtopo: already initialized with rc = %d\n", init_rc);
+        }
+    }
+    return init_rc;
 }