readpass/include/alloc.h

//! Custom allocation framekwork for frozen (RO) and/or secure allocations, shared allocations, aliased allocation, etc. (polymorphic.)
#ifndef _ALLOC_H
#define _ALLOC_H

#ifdef __cplusplus
#include <memory>
#endif

#include "constraints.hh"
#include "types.h"
#include "macros.h"

LINK_START(C)
typedef struct base_allocator alloc_t;

//TODO: C API anonlogue for allocator interface below.

LINK_END

#if $CXX
extern "C" {
	struct base_allocator {
		//TODO: Allocator interface...
		virtual ~base_allocator();
	}
}
namespace alloc {
	class FrozenAllocator : public alloc_t {
		struct _impl;
	protected:
		struct anon_raw_secmem;
		// Untyped deleter
		struct deleter {
			friend class anon_raw_secmem;

			constexpr deleter(const deleter&) noexcept = default;
			constexpr deleter& operator=(const deleter&) noexcept = default;
			constexpr deleter(deleter&&) noexcept = default;
			constexpr deleter& operator=(deleter&&) noexcept = default;

			constexpr void operator()(void* restrict p) const noexcept { return apply_delete(p); }

			virtual ~deleter();
		protected:
			explicit deleter(std::shared_ptr<anon_raw_secmem>&& p);

			template<where::is_polymorphic T>
			constexpr static void* erase_type(T* ptr) noexcept { return dynamic_cast<void*>(ptr); }
			template<where::is_polymorphic T>
			constexpr static void const* erase_type(T const* ptr) noexcept { return dynamic_cast<void const*>(ptr); }
			template<typename T>
			constexpr static void* erase_type_unsafe(T* ptr) noexcept { return static_cast<void*>(ptr); }
			template<typename T>
			constexpr static T* add_type_unsafe(void* ptr) noexcept { return static_cast<T*>(ptr); }
			template<typename T>
			constexpr static void const* erase_type_unsafe(T const* ptr) noexcept { return static_cast<void const*>(ptr); }
			template<typename T>
			constexpr static T const* add_type_unsafe(void const* ptr) noexcept { return static_cast<T const*>(ptr); }
	
			virtual void apply_delete(void* restrict, bool = true) const noexcept;

			inline deleter* finalizer_group_id() const noexcept {
				return m_group_ptr ?: static_cast<deleter*>(this);
			}
			// See dtor impl
			void apply_finalizer_group(std::initializer_list<void*> = {}) noexcept;
			void apply_finalizer_now(std::initializer_list<void*> = {}) noexcept;

			// To prevent anon_raw_secmem being destroyed while there are still allocated values, the base class for the deleter for those values contains a refcount. e.g: `std::unique_ptr<T, deleter_for<T>>` where: `deleter_for<T> final : public deleter { virtual ~deleter_for(); ... };`, or `std::shared_ptr<T>`, where: `std::shared_ptr<value_with_deleter<T>>` aliases-ctor(`old, old->value_ptr()`) -> `std::shared_ptr<T>`
			std::shared_ptr<anon_raw_secmem> m_manager_ref;
		private:
			// Used to sync `this`'s group across copies.
			deleter*  m_group_ptr;
		};
		struct alloc_info;
		struct alloc_value;

		template<typename T>
		struct deleter_for : virtual deleter {
			inline deleter_for(std::shared_ptr<anon_raw_secmem>&& m)
				: deleter(std::move(m)) {}
			virtual ~deleter_for() = default; // This will use deleter's dtor to remove allocations.

			inline void operator()(T* ptr) const noexcept { return apply_delete(deleter::erase_type_unsafe(ptr)); }

		protected:
			inline virtual void apply_delete_typed(T* ptr) const noexcept {
				ptr->~T();
			}
		private:
			inline void apply_delete(void* restrict up) const noexcept override final {
				if constexpr(std::is_trivially_destructible_v<T>) {
					deleter::apply_delete(up); // If the dtor is trivial, ignore it and use default behaviour.
				} else {
					deleter::apply_delete(up, false); // Unlock the memory, but do *not* add it to this deleter's finalizer group.
					apply_delete_typed(static_cast<T*>(up)); // Apply the destructor for `T`
					deleter::apply_finalizer_now({up}); // Get `anon_raw_secmem` to deallocate the memory *now*, instead of at destruction.
				}
			}
		};
	public:
		FrozenAllocator(FrozenAllocator &&) noexcept;
		FrozenAllocator& operator=(FrozenAllocator &&);

		FrozenAllocator(const FrozenAllocator&) = delete;
		FrozenAllocator& operator=(const FrozenAllocator&) = delete;
		virtual ~FrozenAllocator();
	private:
		std::unique_ptr<_impl> inner_;

		/// Manages everything about the actual allocations
		//std::shared_ptr<anon_raw_secmem> m_manager;
		/// A map of values inside the allocator. This is destroyed in reverse order, meaning all the living values are destroyed *before* `m_manager`'d destruction deallocates them.
		//std::map<alloc_info, std::unique_ptr<alloc_value, deleter>> m_values;
	}; 
}
#endif

#endif /* _ALLOC_H */