Avoid allocations during global initialization

Instead, explicitly start lifetime of globals on library initialization. This is achieved by using the new ControlledLifetimeResource class. This can be used as a wrapper around globals to explicitly initialize and shutdown the objects.

This wrapper has been applied to all non-trivial global data in RmlUi. Thus, there should no longer be any memory allocations occurring before `main()` when linking in RmlUi.

We now give a warning if there are objects in user space that refer to any RmlUi resources at the end of `Rml::Shutdown`, as this prevents the library from cleaning up memory pools. Other than the warning, the behavior should be the same as previously.

Breaking change: `Rml::ReleaseMemoryPools` is no longer exposed publicly. This function is automatically called during shutdown and should not be used manually.

Include/RmlUi/Core/Core.h

@@ -180,9 +180,6 @@ RMLUICORE_API void ReleaseCompiledGeometry(RenderInterface* render_interface = n
 /// @note Invalidates all existing FontFaceHandles returned from the font engine.
 RMLUICORE_API void ReleaseFontResources();
 
-/// Forces all memory pools used by RmlUi to be released.
-RMLUICORE_API void ReleaseMemoryPools();
-
 } // namespace Rml
 
 #endif

Include/RmlUi/Core/ElementInstancer.h

@@ -117,5 +117,10 @@ class ElementInstancerGeneric : public ElementInstancer {
 	}
 };
 
+namespace Detail {
+	void InitializeElementInstancerPools();
+	void ShutdownElementInstancerPools();
+} // namespace Detail
+
 } // namespace Rml
 #endif

Include/RmlUi/Core/Factory.h

@@ -71,7 +71,7 @@ enum class EventId : uint16_t;
 class RMLUICORE_API Factory {
 public:
 	/// Initialise the element factory
-	static bool Initialise();
+	static void Initialise();
 	/// Cleanup and shutdown the factory
 	static void Shutdown();
 

Include/RmlUi/Core/ObserverPtr.h

@@ -35,12 +35,16 @@
 
 namespace Rml {
 
-struct RMLUICORE_API ObserverPtrBlock {
-	int num_observers;
-	void* pointed_to_object;
-};
-RMLUICORE_API ObserverPtrBlock* AllocateObserverPtrBlock();
-RMLUICORE_API void DeallocateObserverPtrBlockIfEmpty(ObserverPtrBlock* block);
+namespace Detail {
+	struct RMLUICORE_API ObserverPtrBlock {
+		int num_observers;
+		void* pointed_to_object;
+	};
+	RMLUICORE_API ObserverPtrBlock* AllocateObserverPtrBlock();
+	RMLUICORE_API void DeallocateObserverPtrBlockIfEmpty(ObserverPtrBlock* block);
+	void InitializeObserverPtrPool();
+	void ShutdownObserverPtrPool();
+} // namespace Detail
 
 template <typename T>
 class EnableObserverPtr;
@@ -117,21 +121,21 @@ class RMLUICORE_API ObserverPtr {
 		if (block)
 		{
 			block->num_observers -= 1;
-			DeallocateObserverPtrBlockIfEmpty(block);
+			Detail::DeallocateObserverPtrBlockIfEmpty(block);
 			block = nullptr;
 		}
 	}
 
 private:
 	friend class Rml::EnableObserverPtr<T>;
 
-	explicit ObserverPtr(ObserverPtrBlock* block) noexcept : block(block)
+	explicit ObserverPtr(Detail::ObserverPtrBlock* block) noexcept : block(block)
 	{
 		if (block)
 			block->num_observers += 1;
 	}
 
-	ObserverPtrBlock* block;
+	Detail::ObserverPtrBlock* block;
 };
 
 template <typename T>
@@ -151,7 +155,7 @@ class RMLUICORE_API EnableObserverPtr {
 		if (block)
 		{
 			block->pointed_to_object = nullptr;
-			DeallocateObserverPtrBlockIfEmpty(block);
+			Detail::DeallocateObserverPtrBlockIfEmpty(block);
 		}
 	}
 
@@ -180,13 +184,13 @@ class RMLUICORE_API EnableObserverPtr {
 	{
 		if (!block)
 		{
-			block = AllocateObserverPtrBlock();
+			block = Detail::AllocateObserverPtrBlock();
 			block->num_observers = 0;
 			block->pointed_to_object = static_cast<void*>(static_cast<T*>(this));
 		}
 	}
 
-	ObserverPtrBlock* block = nullptr;
+	Detail::ObserverPtrBlock* block = nullptr;
 };
 
 } // namespace Rml

Include/RmlUi/Core/StyleSheetSpecification.h

@@ -45,8 +45,7 @@ struct DefaultStyleSheetParsers;
 class RMLUICORE_API StyleSheetSpecification {
 public:
 	/// Starts up the specification structure and registers default properties and type parsers.
-	/// @return True if the specification started up successfully, false if not.
-	static bool Initialise();
+	static void Initialise();
 	/// Destroys the specification structure and releases the parsers.
 	static void Shutdown();
 

Include/RmlUi/Core/XMLParser.h

@@ -104,15 +104,9 @@ class RMLUICORE_API XMLParser : public BaseXMLParser {
 	void HandleData(const String& data, XMLDataType type) override;
 
 private:
-	// The header of the document being parsed.
 	UniquePtr<DocumentHeader> header;
-
-	// The active node handler.
 	XMLNodeHandler* active_handler;
-
-	// The parser stack.
-	using ParserStack = Stack<ParseFrame>;
-	ParserStack stack;
+	Stack<ParseFrame> stack;
 };
 
 } // namespace Rml

Source/Core/CMakeLists.txt

@@ -15,6 +15,7 @@ add_library(rmlui_core
 	ContextInstancer.cpp
 	ContextInstancerDefault.cpp
 	ContextInstancerDefault.h
+	ControlledLifetimeResource.h
 	ConvolutionFilter.cpp
 	Core.cpp
 	DataController.cpp
@@ -65,6 +66,8 @@ add_library(rmlui_core
 	ElementHandle.cpp
 	ElementHandle.h
 	ElementInstancer.cpp
+	ElementMeta.cpp
+	ElementMeta.h
 	ElementScroll.cpp
 	ElementStyle.cpp
 	ElementStyle.h

Source/Core/ComputeProperty.cpp

@@ -30,10 +30,29 @@
 #include "../../Include/RmlUi/Core/ComputedValues.h"
 #include "../../Include/RmlUi/Core/Property.h"
 #include "../../Include/RmlUi/Core/StringUtilities.h"
+#include "ControlledLifetimeResource.h"
 
 namespace Rml {
 
-const Style::ComputedValues DefaultComputedValues{nullptr};
+struct ComputedPropertyData {
+	const Style::ComputedValues computed{nullptr};
+};
+static ControlledLifetimeResource<ComputedPropertyData> computed_property_data;
+
+const Style::ComputedValues& DefaultComputedValues()
+{
+	return computed_property_data->computed;
+}
+
+void InitializeComputeProperty()
+{
+	computed_property_data.Initialize();
+}
+
+void ShutdownComputeProperty()
+{
+	computed_property_data.Shutdown();
+}
 
 static constexpr float PixelsPerInch = 96.0f;
 
@@ -114,7 +133,7 @@ float ComputeFontsize(NumericValue value, const Style::ComputedValues& values, c
 		case Unit::REM:
 			// If the current element is a document, the rem unit is relative to the default size.
 			if (!document_values || &values == document_values)
-				return value.number * DefaultComputedValues.font_size();
+				return value.number * DefaultComputedValues().font_size();
 
 			// Otherwise it is relative to the document font size.
 			return value.number * document_values->font_size();

Source/Core/ComputeProperty.h

@@ -67,7 +67,10 @@ uint16_t ComputeBorderWidth(float computed_length);
 
 String GetFontFaceDescription(const String& font_family, Style::FontStyle style, Style::FontWeight weight);
 
-extern const Style::ComputedValues DefaultComputedValues;
+const Style::ComputedValues& DefaultComputedValues();
+
+void InitializeComputeProperty();
+void ShutdownComputeProperty();
 
 } // namespace Rml
 #endif

Source/Core/ControlledLifetimeResource.h

@@ -0,0 +1,86 @@
+/*
+ * This source file is part of RmlUi, the HTML/CSS Interface Middleware
+ *
+ * For the latest information, see http://github.com/mikke89/RmlUi
+ *
+ * Copyright (c) 2019-2024 The RmlUi Team, and contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ */
+
+#ifndef RMLUI_CORE_CONTROLLEDLIFETIMERESOURCE_H
+#define RMLUI_CORE_CONTROLLEDLIFETIMERESOURCE_H
+
+#include "../../Include/RmlUi/Core/Debug.h"
+#include "../../Include/RmlUi/Core/Traits.h"
+
+namespace Rml {
+
+template <typename T>
+class ControlledLifetimeResource : NonCopyMoveable {
+public:
+	ControlledLifetimeResource() = default;
+	~ControlledLifetimeResource() noexcept { RMLUI_ASSERTMSG(!pointer || intentionally_leaked, "Resource was not properly shut down."); }
+
+	explicit operator bool() const noexcept { return pointer != nullptr; }
+
+	void Initialize()
+	{
+		RMLUI_ASSERTMSG(!pointer, "Resource already initialized.");
+		pointer = new T();
+	}
+
+	void InitializeIfEmpty()
+	{
+		if (!pointer)
+			Initialize();
+		else
+			SetIntentionallyLeaked(false);
+	}
+
+	void Leak() { SetIntentionallyLeaked(true); }
+
+	void Shutdown()
+	{
+		RMLUI_ASSERTMSG(pointer, "Shutting down resource that was not initialized, or has been shut down already.");
+		RMLUI_ASSERTMSG(!intentionally_leaked, "Shutting down resource that was marked as leaked.");
+		delete pointer;
+		pointer = nullptr;
+	}
+
+	T* operator->()
+	{
+		RMLUI_ASSERTMSG(pointer, "Resource used before it was initialized, or after it was shut down.");
+		return pointer;
+	}
+
+private:
+#ifdef RMLUI_DEBUG
+	void SetIntentionallyLeaked(bool leaked) { intentionally_leaked = leaked; }
+	bool intentionally_leaked = false;
+#else
+	void SetIntentionallyLeaked(bool /*leaked*/) {}
+#endif
+
+	T* pointer = nullptr;
+};
+
+} // namespace Rml
+#endif