common: SlotVector without generations

src/common/slotVector.h

@@ -1,15 +1,15 @@
 #ifndef EMULATOR_SRC_COMMON_SLOTVECTOR_H_
 #define EMULATOR_SRC_COMMON_SLOTVECTOR_H_
 
-#include "common/assert.h"
-#include "common/abi.h"
+#include "common/common.h"
 
 #include <compare>
 #include <cstdint>
-#include <deque>
 #include <functional>
 #include <limits>
-#include <optional>
+#include <memory>
+#include <new>
+#include <numeric>
 #include <utility>
 #include <vector>
 
@@ -19,105 +19,105 @@ struct SlotId {
 	static constexpr uint32_t INVALID_INDEX = std::numeric_limits<uint32_t>::max();
 
 	constexpr SlotId() noexcept = default;
-	constexpr SlotId(uint32_t value) noexcept: index(value), generation(1) {}
-	constexpr SlotId(uint32_t value, uint32_t slot_generation) noexcept
-	    : index(value), generation(slot_generation) {}
+	constexpr SlotId(uint32_t index) noexcept: index(index) {}
 
-	[[nodiscard]] constexpr explicit operator bool() const noexcept { return index != INVALID_INDEX; }
+	[[nodiscard]] constexpr explicit operator bool() const noexcept {
+		return index != INVALID_INDEX;
+	}
 	constexpr auto operator<=>(const SlotId&) const noexcept = default;
 
 	uint32_t index = INVALID_INDEX;
-	uint32_t generation = 0;
 };
 
-// Stable-address slot storage for cache resources that are intentionally non-movable.
+// Fixed-size chunks keep the stored, non-movable resources in place. Occupancy is a byte per
+// slot, not a bitset: a deferred erase runs while fault threads read other slots.
 template <typename T>
 class SlotVector {
+	static constexpr uint32_t ChunkSize = 256;
+
 public:
 	SlotVector() = default;
 	KYTY_CLASS_NO_COPY(SlotVector);
 
+	~SlotVector() noexcept {
+		ForEach([](SlotId, T& value) { value.~T(); });
+	}
+
 	[[nodiscard]] T& operator[](SlotId id) noexcept {
-		EXIT_IF(!is_allocated(id));
-		return *m_values[id.index].value;
+		return m_chunks[id.index / ChunkSize][id.index % ChunkSize].object;
 	}
 
 	[[nodiscard]] const T& operator[](SlotId id) const noexcept {
-		EXIT_IF(!is_allocated(id));
-		return *m_values[id.index].value;
+		return m_chunks[id.index / ChunkSize][id.index % ChunkSize].object;
 	}
 
 	[[nodiscard]] T* try_get(SlotId id) noexcept {
-		return is_allocated(id) ? &*m_values[id.index].value : nullptr;
+		return is_allocated(id) ? &(*this)[id] : nullptr;
 	}
 
 	[[nodiscard]] const T* try_get(SlotId id) const noexcept {
-		return is_allocated(id) ? &*m_values[id.index].value : nullptr;
+		return is_allocated(id) ? &(*this)[id] : nullptr;
 	}
 
 	[[nodiscard]] bool is_allocated(SlotId id) const noexcept {
-		return id && id.index < m_values.size() &&
-		       m_values[id.index].generation == id.generation && m_values[id.index].value.has_value();
+		return id.index < m_stored.size() && m_stored[id.index] != 0;
 	}
 
 	template <typename... Args>
 	[[nodiscard]] SlotId insert(Args&&... args) {
-		uint32_t index = 0;
 		if (m_free_list.empty()) {
-			index = static_cast<uint32_t>(m_values.size());
-			m_values.emplace_back();
-			m_values.back().value.emplace(std::forward<Args>(args)...);
-		} else {
-			index = m_free_list.back();
-			m_free_list.pop_back();
-			EXIT_IF(m_values[index].value.has_value());
-			m_values[index].value.emplace(std::forward<Args>(args)...);
+			Reserve();
 		}
-		++m_size;
-		return SlotId {index, m_values[index].generation};
+		const uint32_t index = m_free_list.back();
+		m_free_list.pop_back();
+		new (&(*this)[index]) T(std::forward<Args>(args)...);
+		m_stored[index] = 1;
+		return SlotId {index};
 	}
 
 	void erase(SlotId id) noexcept {
-		EXIT_IF(!is_allocated(id));
-		auto& slot = m_values[id.index];
-		slot.value.reset();
-		if (++slot.generation == 0) {
-			slot.generation = 1;
-		}
+		(*this)[id].~T();
+		m_stored[id.index] = 0;
 		m_free_list.push_back(id.index);
-		--m_size;
 	}
 
-	[[nodiscard]] size_t size() const noexcept { return m_size; }
-	[[nodiscard]] size_t capacity() const noexcept { return m_values.size(); }
-
 	template <typename F>
 	void ForEach(F&& fn) {
-		for (uint32_t index = 0; index < m_values.size(); ++index) {
-			if (m_values[index].value) {
-				fn(SlotId {index, m_values[index].generation}, *m_values[index].value);
+		for (uint32_t index = 0; index < m_stored.size(); ++index) {
+			if (m_stored[index] != 0) {
+				fn(SlotId {index}, (*this)[index]);
 			}
 		}
 	}
 
 	template <typename F>
 	void ForEach(F&& fn) const {
-		for (uint32_t index = 0; index < m_values.size(); ++index) {
-			if (m_values[index].value) {
-				fn(SlotId {index, m_values[index].generation}, *m_values[index].value);
+		for (uint32_t index = 0; index < m_stored.size(); ++index) {
+			if (m_stored[index] != 0) {
+				fn(SlotId {index}, (*this)[index]);
 			}
 		}
 	}
 
 private:
-	struct Slot {
-		std::optional<T> value;
-		uint32_t         generation = 1;
+	union Slot {
+		Slot() noexcept {}
+		~Slot() noexcept {}
+
+		T object;
 	};
 
-	std::deque<Slot>             m_values;
-	std::vector<uint32_t>        m_free_list;
-	size_t                       m_size = 0;
+	void Reserve() {
+		const auto first = static_cast<uint32_t>(m_stored.size());
+		m_chunks.push_back(std::make_unique<Slot[]>(ChunkSize));
+		m_stored.resize(first + ChunkSize);
+		m_free_list.resize(ChunkSize);
+		std::iota(m_free_list.rbegin(), m_free_list.rend(), first);
+	}
+
+	std::vector<std::unique_ptr<Slot[]>> m_chunks;
+	std::vector<uint8_t>                 m_stored;
+	std::vector<uint32_t>                m_free_list;
 };
 
 } // namespace Common
@@ -125,7 +125,7 @@ private:
 template <>
 struct std::hash<Common::SlotId> {
 	[[nodiscard]] size_t operator()(Common::SlotId id) const noexcept {
-		return std::hash<uint64_t> {}((static_cast<uint64_t>(id.generation) << 32u) | id.index);
+		return std::hash<uint32_t> {}(id.index);
 	}
 };