1 | // |
2 | // immer: immutable data structures for C++ |
3 | // Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente |
4 | // |
5 | // This software is distributed under the Boost Software License, Version 1.0. |
6 | // See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt |
7 | // |
8 | |
9 | #pragma once |
10 | |
11 | #include <immer/heap/tags.hpp> |
12 | |
13 | #include <memory> |
14 | #include <utility> |
15 | #include <atomic> |
16 | |
17 | namespace immer { |
18 | |
19 | /*! |
20 | * Provides transience ownership tracking when a *tracing garbage |
21 | * collector* is used instead of reference counting. |
22 | * |
23 | * @rst |
24 | * |
25 | * .. warning:: Using this policy without an allocation scheme that |
26 | * includes automatic tracing garbage collection may cause memory |
27 | * leaks. |
28 | * |
29 | * @endrst |
30 | */ |
31 | struct gc_transience_policy |
32 | { |
33 | template <typename HeapPolicy> |
34 | struct apply |
35 | { |
36 | struct type |
37 | { |
38 | using heap_ = typename HeapPolicy::type; |
39 | |
40 | struct edit |
41 | { |
42 | void* v; |
43 | edit() = delete; |
44 | bool operator==(edit x) const { return v == x.v; } |
45 | bool operator!=(edit x) const { return v != x.v; } |
46 | }; |
47 | |
48 | struct owner |
49 | { |
50 | void* make_token_() |
51 | { |
52 | return heap_::allocate(1, norefs_tag{}); |
53 | }; |
54 | |
55 | mutable std::atomic<void*> token_; |
56 | |
57 | operator edit () { return { token_ }; } |
58 | |
59 | owner() |
60 | : token_{make_token_()} |
61 | {} |
62 | owner(const owner& o) |
63 | : token_{make_token_()} |
64 | { |
65 | o.token_ = make_token_(); |
66 | } |
67 | owner(owner&& o) noexcept |
68 | : token_{o.token_.load()} |
69 | {} |
70 | owner& operator=(const owner& o) |
71 | { |
72 | o.token_ = make_token_(); |
73 | token_ = make_token_(); |
74 | return *this; |
75 | } |
76 | owner& operator=(owner&& o) noexcept |
77 | { |
78 | token_ = o.token_.load(); |
79 | return *this; |
80 | } |
81 | }; |
82 | |
83 | struct ownee |
84 | { |
85 | edit token_ {nullptr}; |
86 | |
87 | ownee& operator=(edit e) |
88 | { |
89 | assert(e != noone); |
90 | // This would be a nice safety plug but it sadly |
91 | // does not hold during transient concatenation. |
92 | // assert(token_ == e || token_ == edit{nullptr}); |
93 | token_ = e; |
94 | return *this; |
95 | } |
96 | |
97 | bool can_mutate(edit t) const { return token_ == t; } |
98 | bool owned() const { return token_ != edit{nullptr}; } |
99 | }; |
100 | |
101 | static owner noone; |
102 | }; |
103 | }; |
104 | }; |
105 | |
106 | template <typename HP> |
107 | typename gc_transience_policy::apply<HP>::type::owner |
108 | gc_transience_policy::apply<HP>::type::noone = {}; |
109 | |
110 | } // namespace immer |
111 | |