a portable thread class (#1081)

* a portable thread class

* Update platform.h.in

* Update platform.h.in

src/platform.h.in

@@ -28,6 +28,7 @@
 #ifdef _WIN32
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
+#include <process.h>
 #else
 #include <pthread.h>
 #endif
@@ -96,6 +97,39 @@ private:
 };
 #endif // _WIN32
 
+#if _WIN32
+static unsigned __stdcall start_wrapper(void* args);
+class Thread
+{
+public:
+    Thread(void* (*start)(void*), void* args = 0) { _start = start; _args = args; handle = (HANDLE)_beginthreadex(0, 0, start_wrapper, this, 0, 0); }
+    ~Thread() {}
+    void join() { WaitForSingleObject(handle, INFINITE); CloseHandle(handle); }
+private:
+    friend static unsigned __stdcall start_wrapper(void* arg);
+    HANDLE handle;
+    void* (*_start)(void*);
+    void* _args;
+};
+
+static unsigned __stdcall start_wrapper(void* args)
+{
+    Thread* t = (Thread*)args;
+    t->_start(t->_args);
+    return 0;
+}
+#else // _WIN32
+class Thread
+{
+public:
+    Thread(void* (*start)(void*), void* args = 0) { pthread_create(&t, 0, start, args); }
+    ~Thread() {}
+    void join() { pthread_join(t, 0); }
+private:
+    pthread_t t;
+};
+#endif // _WIN32
+
 } // namespace ncnn
 
 #endif // NCNN_PLATFORM_H