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author | Vincent Ambo <mail@tazj.in> | 2020-07-15T07·20+0100 |
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committer | Vincent Ambo <mail@tazj.in> | 2020-07-15T07·23+0100 |
commit | 1213b086a1015a662ab7ebd658f784534fd3116a (patch) | |
tree | d3bc8f3b7f40b8b60f0ef6fbd649cf765f4fdfb6 /third_party/immer/immer/heap/free_list_heap.hpp | |
parent | 1390827b9ea1e04bc9863e48930bfd16db3b716e (diff) | |
parent | 7f19d641647ac4ef313ed88d6b5c140983ce5436 (diff) |
merge(3p/immer): Subtree merge at 'ad3e3556d' as 'third_party/immer' r/1299
Change-Id: I9636a41ad44b4218293833fd3e9456d9b07c731b
Diffstat (limited to 'third_party/immer/immer/heap/free_list_heap.hpp')
-rw-r--r-- | third_party/immer/immer/heap/free_list_heap.hpp | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/third_party/immer/immer/heap/free_list_heap.hpp b/third_party/immer/immer/heap/free_list_heap.hpp new file mode 100644 index 0000000000..dc25b10184 --- /dev/null +++ b/third_party/immer/immer/heap/free_list_heap.hpp @@ -0,0 +1,83 @@ +// +// 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 <immer/heap/free_list_node.hpp> +#include <immer/heap/with_data.hpp> + +#include <atomic> +#include <cassert> + +namespace immer { + +/*! + * Adaptor that does not release the memory to the parent heap but + * instead it keeps the memory in a thread-safe global free list. Must + * be preceded by a `with_data<free_list_node, ...>` heap adaptor. + * + * @tparam Size Maximum size of the objects to be allocated. + * @tparam Base Type of the parent heap. + */ +template <std::size_t Size, std::size_t Limit, typename Base> +struct free_list_heap : Base +{ + 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)); + + free_list_node* n; + do { + n = head().data; + if (!n) { + auto p = base_t::allocate(Size + sizeof(free_list_node)); + return static_cast<free_list_node*>(p); + } + } while (!head().data.compare_exchange_weak(n, n->next)); + head().count.fetch_sub(1u, std::memory_order_relaxed); + 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)); + + // we use relaxed, because we are fine with temporarily having + // a few more/less buffers in free list + if (head().count.load(std::memory_order_relaxed) >= Limit) { + base_t::deallocate(Size + sizeof(free_list_node), data); + } else { + auto n = static_cast<free_list_node*>(data); + do { + n->next = head().data; + } while (!head().data.compare_exchange_weak(n->next, n)); + head().count.fetch_add(1u, std::memory_order_relaxed); + } + } + +private: + struct head_t + { + std::atomic<free_list_node*> data; + std::atomic<std::size_t> count; + }; + + static head_t& head() + { + static head_t head_{{nullptr}, {0}}; + return head_; + } +}; + +} // namespace immer |