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//
// immer: immutable data structures for C++
// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
//
// This software is distributed under the Boost Software License, Version 1.0.
// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
//
#pragma once
#include <cassert>
#include <immer/config.hpp>
#include <immer/heap/free_list_node.hpp>
namespace immer {
namespace detail {
template <typename Heap>
struct unsafe_free_list_storage
{
struct head_t
{
free_list_node* data;
std::size_t count;
};
static head_t& head()
{
static head_t head_{nullptr, 0};
return head_;
}
};
template <template <class> class Storage,
std::size_t Size,
std::size_t Limit,
typename Base>
class unsafe_free_list_heap_impl : Base
{
using storage = Storage<unsafe_free_list_heap_impl>;
public:
using base_t = Base;
template <typename... Tags>
static void* allocate(std::size_t size, Tags...)
{
assert(size <= sizeof(free_list_node) + Size);
assert(size >= sizeof(free_list_node));
auto n = storage::head().data;
if (!n) {
auto p = base_t::allocate(Size + sizeof(free_list_node));
return static_cast<free_list_node*>(p);
}
--storage::head().count;
storage::head().data = n->next;
return n;
}
template <typename... Tags>
static void deallocate(std::size_t size, void* data, Tags...)
{
assert(size <= sizeof(free_list_node) + Size);
assert(size >= sizeof(free_list_node));
if (storage::head().count >= Limit)
base_t::deallocate(Size + sizeof(free_list_node), data);
else {
auto n = static_cast<free_list_node*>(data);
n->next = storage::head().data;
storage::head().data = n;
++storage::head().count;
}
}
static void clear()
{
while (storage::head().data) {
auto n = storage::head().data->next;
base_t::deallocate(Size + sizeof(free_list_node),
storage::head().data);
storage::head().data = n;
--storage::head().count;
}
}
};
} // namespace detail
/*!
* Adaptor that does not release the memory to the parent heap but
* instead it keeps the memory in a global free list that **is not
* thread-safe**. Must be preceded by a `with_data<free_list_node,
* ...>` heap adaptor.
*
* @tparam Size Maximum size of the objects to be allocated.
* @tparam Limit Maximum number of elements to keep in the free list.
* @tparam Base Type of the parent heap.
*/
template <std::size_t Size, std::size_t Limit, typename Base>
struct unsafe_free_list_heap
: detail::unsafe_free_list_heap_impl<detail::unsafe_free_list_storage,
Size,
Limit,
Base>
{};
} // namespace immer
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