memory_resource.cpp revision 314564 
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
26class _LIBCPP_TYPE_VIS __new_delete_memory_resource_imp
27    : public memory_resource
28{
29public:
30    ~__new_delete_memory_resource_imp() = default;
31
32protected:
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        { _VSTD::__libcpp_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
45class _LIBCPP_TYPE_VIS __null_memory_resource_imp
46    : public memory_resource
47{
48public:
49    ~__null_memory_resource_imp() = default;
50
51protected:
52    virtual void* do_allocate(size_t, size_t) {
53        __throw_bad_alloc();
54    }
55    virtual void do_deallocate(void *, size_t, size_t) {}
56    virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
57    { return &__other == this; }
58};
59
60namespace {
61
62union ResourceInitHelper {
63  struct {
64    __new_delete_memory_resource_imp new_delete_res;
65    __null_memory_resource_imp       null_res;
66  } resources;
67  char dummy;
68  _LIBCPP_CONSTEXPR_AFTER_CXX11 ResourceInitHelper() : resources() {}
69  ~ResourceInitHelper() {}
70};
71// When compiled in C++14 this initialization should be a constant expression.
72// Only in C++11 is "init_priority" needed to ensure initialization order.
73#if _LIBCPP_STD_VER > 11
74_LIBCPP_SAFE_STATIC
75#endif
76ResourceInitHelper res_init  __attribute__((init_priority (101)));
77
78} // end namespace
79
80
81memory_resource * new_delete_resource() _NOEXCEPT {
82    return &res_init.resources.new_delete_res;
83}
84
85memory_resource * null_memory_resource() _NOEXCEPT {
86    return &res_init.resources.null_res;
87}
88
89// default_memory_resource()
90
91static memory_resource *
92__default_memory_resource(bool set = false, memory_resource * new_res = nullptr) _NOEXCEPT
93{
94#ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
95    _LIBCPP_SAFE_STATIC static atomic<memory_resource*> __res =
96        ATOMIC_VAR_INIT(&res_init.resources.new_delete_res);
97    if (set) {
98        new_res = new_res ? new_res : new_delete_resource();
99        // TODO: Can a weaker ordering be used?
100        return _VSTD::atomic_exchange_explicit(
101            &__res, new_res, memory_order::memory_order_acq_rel);
102    }
103    else {
104        return _VSTD::atomic_load_explicit(
105            &__res, memory_order::memory_order_acquire);
106    }
107#elif !defined(_LIBCPP_HAS_NO_THREADS)
108    _LIBCPP_SAFE_STATIC static memory_resource * res = &res_init.resources.new_delete_res;
109    static mutex res_lock;
110    if (set) {
111        new_res = new_res ? new_res : new_delete_resource();
112        lock_guard<mutex> guard(res_lock);
113        memory_resource * old_res = res;
114        res = new_res;
115        return old_res;
116    } else {
117        lock_guard<mutex> guard(res_lock);
118        return res;
119    }
120#else
121    _LIBCPP_SAFE_STATIC static memory_resource* res = &res_init.resources.new_delete_res;
122    if (set) {
123        new_res = new_res ? new_res : new_delete_resource();
124        memory_resource * old_res = res;
125        res = new_res;
126        return old_res;
127    } else {
128        return res;
129    }
130#endif
131}
132
133memory_resource * get_default_resource() _NOEXCEPT
134{
135    return __default_memory_resource();
136}
137
138memory_resource * set_default_resource(memory_resource * __new_res) _NOEXCEPT
139{
140    return __default_memory_resource(true, __new_res);
141}
142
143_LIBCPP_END_NAMESPACE_LFTS_PMR
144