1 //===------------------------ memory_resource.cpp -------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "experimental/memory_resource"
11 
12 #ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
13 #include "atomic"
14 #elif !defined(_LIBCPP_HAS_NO_THREADS)
15 #include "mutex"
16 #endif
17 
18 _LIBCPP_BEGIN_NAMESPACE_LFTS_PMR
19 
20 // memory_resource
21 
22 //memory_resource::~memory_resource() {}
23 
24 // new_delete_resource()
25 
26 class _LIBCPP_TYPE_VIS_ONLY __new_delete_memory_resource_imp
27     : public memory_resource
28 {
29 public:
30     ~__new_delete_memory_resource_imp() = default;
31 
32 protected:
33     virtual void* do_allocate(size_t __size, size_t __align)
34         { return __allocate(__size); }
35 
36     virtual void do_deallocate(void * __p, size_t, size_t)
37         { __deallocate(__p); }
38 
39     virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
40         { return &__other == this; }
41 };
42 
43 // null_memory_resource()
44 
45 class _LIBCPP_TYPE_VIS_ONLY __null_memory_resource_imp
46     : public memory_resource
47 {
48 public:
49     ~__null_memory_resource_imp() = default;
50 
51 protected:
52     virtual void* do_allocate(size_t, size_t) {
53 #ifndef _LIBCPP_NO_EXCEPTIONS
54         throw std::bad_alloc();
55 #else
56         abort();
57 #endif
58     }
59     virtual void do_deallocate(void *, size_t, size_t) {}
60     virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
61     { return &__other == this; }
62 };
63 
64 union ResourceInitHelper {
65   struct {
66     __new_delete_memory_resource_imp new_delete_res;
67     __null_memory_resource_imp       null_res;
68   } resources;
69   char dummy;
70   _LIBCPP_CONSTEXPR_AFTER_CXX11 ResourceInitHelper() : resources() {}
71   ~ResourceInitHelper() {}
72 };
73 // When compiled in C++14 this initialization should be a constant expression.
74 // Only in C++11 is "init_priority" needed to ensure initialization order.
75 ResourceInitHelper res_init __attribute__((init_priority (101)));
76 
77 memory_resource * new_delete_resource() _NOEXCEPT {
78     return &res_init.resources.new_delete_res;
79 }
80 
81 memory_resource * null_memory_resource() _NOEXCEPT {
82     return &res_init.resources.null_res;
83 }
84 
85 // default_memory_resource()
86 
87 static memory_resource *
88 __default_memory_resource(bool set = false, memory_resource * new_res = nullptr) _NOEXCEPT
89 {
90 #ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
91     static atomic<memory_resource*> __res =
92         ATOMIC_VAR_INIT(&res_init.resources.new_delete_res);
93     if (set) {
94         new_res = new_res ? new_res : new_delete_resource();
95         // TODO: Can a weaker ordering be used?
96         return _VSTD::atomic_exchange_explicit(
97             &__res, new_res, memory_order::memory_order_acq_rel);
98     }
99     else {
100         return _VSTD::atomic_load_explicit(
101             &__res, memory_order::memory_order_acquire);
102     }
103 #elif !defined(_LIBCPP_HAS_NO_THREADS)
104     static memory_resource * res = &res_init.resources.new_delete_res;
105     static mutex res_lock;
106     if (set) {
107         new_res = new_res ? new_res : new_delete_resource();
108         lock_guard<mutex> guard(res_lock);
109         memory_resource * old_res = res;
110         res = new_res;
111         return old_res;
112     } else {
113         lock_guard<mutex> guard(res_lock);
114         return res;
115     }
116 #else
117     static memory_resource* res = &res_init.resources.new_delete_res;
118     if (set) {
119         new_res = new_res ? new_res : new_delete_resource();
120         memory_resource * old_res = res;
121         res = new_res;
122         return old_res;
123     } else {
124         return res;
125     }
126 #endif
127 }
128 
129 memory_resource * get_default_resource() _NOEXCEPT
130 {
131     return __default_memory_resource();
132 }
133 
134 memory_resource * set_default_resource(memory_resource * __new_res) _NOEXCEPT
135 {
136     return __default_memory_resource(true, __new_res);
137 }
138 
139 _LIBCPP_END_NAMESPACE_LFTS_PMR