Add WeakPtr. Use WeakPtr in ModuleWidget context menu. Fix crash when displaying preset menu when the preset folder does not exist.

include/weakptr.hpp

@@ -0,0 +1,104 @@
+#pragma once
+#include <common.hpp>
+#include <atomic>
+
+
+namespace rack {
+
+
+struct WeakHandle {
+	void* ptr;
+	std::atomic<size_t> count{0};
+	WeakHandle(void* ptr) : ptr(ptr) {}
+};
+
+
+/** Base class for classes that allow WeakPtrs to be used.
+*/
+struct WeakBase {
+	WeakHandle* weakHandle = nullptr;
+
+	~WeakBase() {
+		if (weakHandle) {
+			weakHandle->ptr = nullptr;
+		}
+	}
+	size_t getWeakCount() {
+		if (!weakHandle)
+			return 0;
+		return weakHandle->count;
+	}
+};
+
+
+/** A weak pointer to a subclass of WeakBase.
+Weak pointers behave like raw pointers but can be accessed safely (returning nullptr) after the pointed object is deleted.
+
+Example:
+
+	Foo* foo = new Foo;
+	WeakPtr<Foo> weakFoo = foo;
+	weakFoo.get(); // returns foo
+	delete foo;
+	weakFoo.get(); // returns nullptr
+
+Caveat: In multithreaded environments, the object pointed to by the WeakPtr could be deleted at any time after obtaining its pointer from WeakPtr.
+*/
+template <typename T>
+struct WeakPtr {
+	WeakHandle* weakHandle = NULL;
+
+	WeakPtr() {}
+	WeakPtr(T* ptr) {
+		set(ptr);
+	}
+	WeakPtr& operator=(const WeakPtr& other) {
+		set(other.get());
+		return *this;
+	}
+	~WeakPtr() {
+		set(nullptr);
+	}
+	void set(T* ptr) {
+		// Release handle
+		if (weakHandle) {
+			// Decrement and check handle reference count
+			if (--weakHandle->count == 0) {
+				// Remove handle from object and delete it
+				T* oldPtr = reinterpret_cast<T*>(weakHandle->ptr);
+				if (oldPtr) {
+					oldPtr->weakHandle = nullptr;
+				}
+				delete weakHandle;
+			}
+			weakHandle = nullptr;
+		}
+		// Obtain handle
+		if (ptr) {
+			if (!ptr->weakHandle) {
+				// Create new handle for object
+				ptr->weakHandle = new WeakHandle(ptr);
+			}
+			weakHandle = ptr->weakHandle;
+			// Increment handle reference count
+			weakHandle->count++;
+		}
+	}
+	T* get() const {
+		if (!weakHandle)
+			return nullptr;
+		return reinterpret_cast<T*>(weakHandle->ptr);
+	}
+	T& operator*() const {
+		return *get();
+	}
+	T* operator->() const {
+		return get();
+	}
+	explicit operator bool() const {
+		return get();
+	}
+};
+
+
+} // namespace rack

include/widget/Widget.hpp

@@ -6,6 +6,7 @@
 #include <window.hpp>
 #include <color.hpp>
 #include <event.hpp>
+#include <weakptr.hpp>
 
 
 namespace rack {
@@ -20,7 +21,7 @@ namespace widget {
 The bounding box of a Widget is a rectangle specified by `box` relative to their parent.
 The appearance is defined by overriding `draw()`, and the behavior is defined by overriding `step()` and `on*()` event handlers.
 */
-struct Widget {
+struct Widget : WeakBase {
 	/** Stores position and size */
 	math::Rect box = math::Rect(math::Vec(), math::Vec(INFINITY, INFINITY));
 	/** Automatically set when Widget is added as a child to another Widget */

src/app/ModuleWidget.cpp

@@ -151,73 +151,91 @@ struct ModuleInfoItem : ui::MenuItem {
 
 
 struct ModuleDisconnectItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->disconnectAction();
 	}
 };
 
 
 struct ModuleResetItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->resetAction();
 	}
 };
 
 
 struct ModuleRandomizeItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->randomizeAction();
 	}
 };
 
 
 struct ModuleCopyItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->copyClipboard();
 	}
 };
 
 
 struct ModulePasteItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->pasteClipboardAction();
 	}
 };
 
 
 struct ModuleSaveItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->saveDialog();
 	}
 };
 
 
 struct ModuleSaveTemplateItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->saveTemplate();
 	}
 };
 
 
 struct ModuleLoadItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->loadDialog();
 	}
 };
 
 
 struct ModulePresetPathItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	std::string presetPath;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		try {
 			moduleWidget->loadAction(presetPath);
 		}
@@ -229,8 +247,10 @@ struct ModulePresetPathItem : ui::MenuItem {
 
 
 struct ModulePresetItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	ui::Menu* createChildMenu() override {
+		if (!moduleWidget)
+			return NULL;
 		ui::Menu* menu = new ui::Menu;
 
 		ModuleCopyItem* copyItem = new ModuleCopyItem;
@@ -264,21 +284,23 @@ struct ModulePresetItem : ui::MenuItem {
 		auto createPresetItems = [&](std::string presetDir) {
 			bool hasPresets = false;
 			// Note: This is not cached, so opening this menu each time might have a bit of latency.
-			for (const std::string& presetPath : system::getEntries(presetDir)) {
-				if (system::getExtension(presetPath) != ".vcvm")
-					continue;
-				hasPresets = true;
-
-				std::string presetName = system::getStem(presetPath);
-				// Remove "1_", "42_", "001_", etc at the beginning of preset filenames
-				std::regex r("^\\d*_");
-				presetName = std::regex_replace(presetName, r, "");
-
-				ModulePresetPathItem* presetItem = new ModulePresetPathItem;
-				presetItem->text = presetName;
-				presetItem->presetPath = presetPath;
-				presetItem->moduleWidget = moduleWidget;
-				menu->addChild(presetItem);
+			if (system::isDirectory(presetDir)) {
+				for (const std::string& presetPath : system::getEntries(presetDir)) {
+					if (system::getExtension(presetPath) != ".vcvm")
+						continue;
+					hasPresets = true;
+
+					std::string presetName = system::getStem(presetPath);
+					// Remove "1_", "42_", "001_", etc at the beginning of preset filenames
+					std::regex r("^\\d*_");
+					presetName = std::regex_replace(presetName, r, "");
+
+					ModulePresetPathItem* presetItem = new ModulePresetPathItem;
+					presetItem->text = presetName;
+					presetItem->presetPath = presetPath;
+					presetItem->moduleWidget = moduleWidget;
+					menu->addChild(presetItem);
+				}
 			}
 			if (!hasPresets) {
 				menu->addChild(createMenuLabel("(None)"));
@@ -301,24 +323,30 @@ struct ModulePresetItem : ui::MenuItem {
 
 
 struct ModuleCloneItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->cloneAction();
 	}
 };
 
 
 struct ModuleBypassItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->bypassAction();
 	}
 };
 
 
 struct ModuleDeleteItem : ui::MenuItem {
-	ModuleWidget* moduleWidget;
+	WeakPtr<ModuleWidget> moduleWidget;
 	void onAction(const event::Action& e) override {
+		if (!moduleWidget)
+			return;
 		moduleWidget->removeAction();
 	}
 };