Add CallOnce which is a clone or wrapper of std::call_once

src/cpu.cpp

@@ -1932,15 +1932,10 @@ static void initialize_global_cpu_info()
 #endif // defined __ANDROID__ || defined __linux__
 }
 
-static int g_cpu_info_initialized = 0;
-
 static inline void try_initialize_global_cpu_info()
 {
-    if (!g_cpu_info_initialized)
-    {
-        initialize_global_cpu_info();
-        g_cpu_info_initialized = 1;
-    }
+    static ncnn::OnceFlag flag = OnceFlagInit;
+    ncnn::CallOnce(flag, &initialize_global_cpu_info);
 }
 
 namespace ncnn {

src/platform.h.in

@@ -77,6 +77,9 @@
 #else
 #include <pthread.h>
 #endif
+#if (__cplusplus >= 201103L) && !NCNN_SIMPLESTL
+#include <mutex>
+#endif
 #endif // NCNN_THREADS
 
 #if __ANDROID_API__ >= 26
@@ -141,6 +144,22 @@ public:
 private:
     DWORD key;
 };
+
+#if (__cplusplus < 201103L) || NCNN_SIMPLESTL
+typedef INIT_ONCE OnceFlag;
+#define OnceFlagInit INIT_ONCE_STATIC_INIT
+
+static inline int CallOnce(OnceFlag &flag, void (*init_routine)(void))
+{
+    BOOL pending = FALSE;
+    InitOnceBeginInitialize(&flag, 0, &pending, NULL);
+    if (pending)
+        init_routine();
+    InitOnceComplete(&flag, 0, NULL);
+    return 0;
+}
+#endif // < c++11
+
 #else // defined _WIN32
 class NCNN_EXPORT Mutex
 {
@@ -186,7 +205,30 @@ public:
 private:
     pthread_key_t key;
 };
+
+#if (__cplusplus < 201103L) || NCNN_SIMPLESTL
+typedef pthread_once_t OnceFlag;
+#define OnceFlagInit PTHREAD_ONCE_INIT
+
+static inline int CallOnce(OnceFlag &flag, void (*init_routine)(void))
+{
+    return pthread_once(&flag, init_routine);
+}
+#endif // < c++11
+
 #endif // defined _WIN32
+
+#if (__cplusplus >= 201103L) && !NCNN_SIMPLESTL
+using OnceFlag = std::once_flag;
+#define OnceFlagInit {}
+
+static inline int CallOnce(OnceFlag &flag, void (*init_routine)(void))
+{
+    std::call_once(flag, init_routine);
+    return 0;
+}
+#endif // >= c++11
+
 #else // NCNN_THREADS
 class NCNN_EXPORT Mutex
 {
@@ -225,6 +267,21 @@ public:
 private:
     void* data;
 };
+
+typedef bool OnceFlag;
+#define OnceFlagInit false
+
+static inline int CallOnce(OnceFlag &flag, void (*init_routine)(void))
+{
+    if (!flag)
+    {
+        init_routine();
+        flag = true;
+    }
+
+    return 0;
+}
+
 #endif // NCNN_THREADS
 
 class NCNN_EXPORT MutexLockGuard

tests/CMakeLists.txt

@@ -60,6 +60,7 @@ endif()
 
 ncnn_add_test(c_api)
 ncnn_add_test(cpu)
+ncnn_add_test(platform)
 
 if(NCNN_VULKAN)
     ncnn_add_test(command)

tests/test_platform.cpp

@@ -0,0 +1,33 @@
+#include <stdlib.h>
+
+#include "platform.h"
+
+static int g_once_count = 0;
+
+static void init()
+{
+    g_once_count++;
+}
+
+int test_call_once()
+{
+    static ncnn::OnceFlag flag = OnceFlagInit;
+    ncnn::CallOnce(flag, &init);
+    ncnn::CallOnce(flag, &init);
+    ncnn::CallOnce(flag, &init);
+
+    if (g_once_count != 1)
+        return EXIT_FAILURE;
+    return EXIT_SUCCESS;
+}
+
+int main()
+{
+    int ret;
+
+    ret = test_call_once();
+    if (ret)
+        return ret;
+
+    return 0;
+}