1 files changed, 129 insertions, 6 deletions

diff --git a/zen/globals.h b/zen/globals.h
index 10975414..024147fa 100755
--- a/zen/globals.h
+++ b/zen/globals.h
@@ -14,14 +14,22 @@
 
 namespace zen
 {
-//solve static destruction order fiasco by providing shared ownership and serialized access to global variables
+/*
+Solve static destruction order fiasco by providing shared ownership and serialized access to global variables
+
+=>there may be accesses to "Global<T>::get()" during process shutdown e.g. _("") used by message in debug_minidump.cpp or by some detached thread assembling an error message!
+=> use trivially-destructible POD only!!!
+
+ATTENTION: function-static globals have the compiler generate "magic statics" == compiler-genenerated locking code which will crash or leak memory when accessed after global is "dead"
+           => "solved" by FunStatGlobal, but we can't have "too many" of these...
+*/
 template <class T>
-class Global
+class Global //don't use for function-scope statics!
 {
 public:
     Global()
     {
-        static_assert(std::is_trivially_destructible_v<Pod>, "this memory needs to live forever");
+        static_assert(std::is_trivially_constructible_v<Pod>&& std::is_trivially_destructible_v<Pod>, "this memory needs to live forever");
         assert(!pod_.inst && !pod_.spinLock); //we depend on static zero-initialization!
     }
 
@@ -52,16 +60,131 @@ public:
     }
 
 private:
-    //avoid static destruction order fiasco: there may be accesses to "Global<T>::get()" during process shutdown
-    //e.g. _("") used by message in debug_minidump.cpp or by some detached thread assembling an error message!
-    //=> use trivially-destructible POD only!!!
     struct Pod
     {
+        std::atomic<bool> spinLock; // { false }; rely entirely on static zero-initialization! => avoid potential contention with worker thread during Global<> construction!
+        //serialize access; can't use std::mutex: has non-trival destructor
         std::shared_ptr<T>* inst;   // = nullptr;
+    } pod_;
+};
+
+//===================================================================================================================
+//===================================================================================================================
+
+struct CleanUpEntry
+{
+    using CleanUpFunction = void (*)(void* callbackData);
+    CleanUpFunction cleanUpFun;
+    void*           callbackData;
+    CleanUpEntry*   prev;
+};
+void registerGlobalForDestruction(CleanUpEntry& entry);
+
+
+template <class T>
+class FunStatGlobal
+{
+public:
+    //No FunStatGlobal() or ~FunStatGlobal()!
+
+    std::shared_ptr<T> get()
+    {
+        static_assert(std::is_trivially_constructible_v<FunStatGlobal>&&
+                      std::is_trivially_destructible_v<FunStatGlobal>, "this class must not generate code for magic statics!");
+
+        while (pod_.spinLock.exchange(true)) ;
+        ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
+        if (pod_.inst)
+            return *pod_.inst;
+        return nullptr;
+    }
+
+    void set(std::unique_ptr<T>&& newInst)
+    {
+        std::shared_ptr<T>* tmpInst = nullptr;
+        if (newInst)
+            tmpInst = new std::shared_ptr<T>(std::move(newInst));
+        {
+            while (pod_.spinLock.exchange(true)) ;
+            ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
+
+            std::swap(pod_.inst, tmpInst);
+            registerDestruction();
+        }
+        delete tmpInst;
+    }
+
+    void initOnce(std::unique_ptr<T> (*getInitialValue)())
+    {
+        while (pod_.spinLock.exchange(true)) ;
+        ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
+
+        if (!pod_.cleanUpEntry.cleanUpFun)
+        {
+            assert(!pod_.inst);
+            if (std::unique_ptr<T> newInst = (*getInitialValue)())
+                pod_.inst = new std::shared_ptr<T>(std::move(newInst));
+            registerDestruction();
+        }
+    }
+
+private:
+    //call while holding pod_.spinLock
+    void registerDestruction()
+    {
+        assert(pod_.spinLock);
+
+        if (!pod_.cleanUpEntry.cleanUpFun)
+        {
+            pod_.cleanUpEntry.callbackData = this;
+            pod_.cleanUpEntry.cleanUpFun = [](void* callbackData)
+            {
+                auto thisPtr = static_cast<FunStatGlobal*>(callbackData);
+                thisPtr->set(nullptr);
+            };
+
+            registerGlobalForDestruction(pod_.cleanUpEntry);
+        }
+    }
+
+    struct Pod
+    {
         std::atomic<bool> spinLock; // { false }; rely entirely on static zero-initialization! => avoid potential contention with worker thread during Global<> construction!
         //serialize access; can't use std::mutex: has non-trival destructor
+        std::shared_ptr<T>* inst;   // = nullptr;
+        CleanUpEntry cleanUpEntry;
     } pod_;
 };
+
+
+inline
+void registerGlobalForDestruction(CleanUpEntry& entry)
+{
+    static struct
+    {
+        std::atomic<bool> spinLock;
+        CleanUpEntry*     head;
+    } cleanUpList;
+
+    static_assert(std::is_trivially_constructible_v<decltype(cleanUpList)>&&
+                  std::is_trivially_destructible_v<decltype(cleanUpList)>, "we must not generate code for magic statics!");
+
+    while (cleanUpList.spinLock.exchange(true)) ;
+    ZEN_ON_SCOPE_EXIT(cleanUpList.spinLock = false);
+
+    std::atexit([]
+    {
+        while (cleanUpList.spinLock.exchange(true)) ;
+        ZEN_ON_SCOPE_EXIT(cleanUpList.spinLock = false);
+
+        (*cleanUpList.head->cleanUpFun)(cleanUpList.head->callbackData);
+        cleanUpList.head = cleanUpList.head->prev; //nicely clean up in reverse order of construction
+    });
+
+    entry.prev = cleanUpList.head;
+    cleanUpList.head = &entry;
+
+}
 }
 
 #endif //GLOBALS_H_8013740213748021573485