From 73ad6a97531b6bc1d311eceb6ba2770fdf407b81 Mon Sep 17 00:00:00 2001
From: Willem Jan Palenstijn <Willem.Jan.Palenstijn@cwi.nl>
Date: Tue, 17 May 2016 11:22:17 +0200
Subject: Avoid defining singleton construction in header file

That way, the call to new is always executed by code inside libastra.
This avoids the situation where a singleton gets created by a copy
of the constructor linked into an object file outside of libastra, such
as a .mex file, which would then also cause the vtable to be outside of
libastra. This situation would cause issues when .mex files are unloaded.
---
 include/astra/Singleton.h | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/astra/Singleton.h b/include/astra/Singleton.h
index a256187..1ef4bba 100644
--- a/include/astra/Singleton.h
+++ b/include/astra/Singleton.h
@@ -57,15 +57,17 @@ class Singleton {
 			m_singleton = 0;
 		}
 
+		static void construct();
+
 		// get singleton
 		static T& getSingleton() {
 			if (!m_singleton)
-				m_singleton = new T();
+				construct();
 			return *m_singleton;
 		}
 		static T* getSingletonPtr() {
 			if (!m_singleton)
-				m_singleton = new T();
+				construct();
 			return m_singleton;
 		}
 
@@ -76,11 +78,23 @@ class Singleton {
 
 };
 
-#define DEFINE_SINGLETON(T) template<> T* Singleton<T >::m_singleton = 0
+// We specifically avoid defining construct() in the header.
+// That way, the call to new is always executed by code inside libastra.
+// This avoids the situation where a singleton gets created by a copy
+// of the constructor linked into an object file outside of libastra, such
+// as a .mex file, which would then also cause the vtable to be outside of
+// libastra. This situation would cause issues when .mex files are unloaded.
+
+#define DEFINE_SINGLETON(T) \
+template<> void Singleton<T >::construct() { m_singleton = new T(); } \
+template<> T* Singleton<T >::m_singleton = 0
+
 
 // This is a hack to support statements like
 // DEFINE_SINGLETON2(CTemplatedClass<C1, C2>);
-#define DEFINE_SINGLETON2(A,B) template<> A,B* Singleton<A,B >::m_singleton = 0
+#define DEFINE_SINGLETON2(A,B) \
+template<> void Singleton<A,B >::construct() { m_singleton = new A,B(); } \
+template<> A,B* Singleton<A,B >::m_singleton = 0
 
 } // end namespace
 
-- 
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