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      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 __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 _VSTD::__libcpp_allocate(__size, __align); /* FIXME */}
     35 
     36     virtual void do_deallocate(void* __p, size_t __n, size_t __align) {
     37       _VSTD::__libcpp_deallocate(__p, __n, __align); /* FIXME */
     38     }
     39 
     40     virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
     41         { return &__other == this; }
     42 };
     43 
     44 // null_memory_resource()
     45 
     46 class _LIBCPP_TYPE_VIS __null_memory_resource_imp
     47     : public memory_resource
     48 {
     49 public:
     50     ~__null_memory_resource_imp() = default;
     51 
     52 protected:
     53     virtual void* do_allocate(size_t, size_t) {
     54         __throw_bad_alloc();
     55     }
     56     virtual void do_deallocate(void *, size_t, size_t) {}
     57     virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
     58     { return &__other == this; }
     59 };
     60 
     61 namespace {
     62 
     63 union ResourceInitHelper {
     64   struct {
     65     __new_delete_memory_resource_imp new_delete_res;
     66     __null_memory_resource_imp       null_res;
     67   } resources;
     68   char dummy;
     69   _LIBCPP_CONSTEXPR_AFTER_CXX11 ResourceInitHelper() : resources() {}
     70   ~ResourceInitHelper() {}
     71 };
     72 
     73 // Detect if the init_priority attribute is supported.
     74 #if (defined(_LIBCPP_COMPILER_GCC) && defined(__APPLE__)) \
     75   || defined(_LIBCPP_COMPILER_MSVC)
     76 // GCC on Apple doesn't support the init priority attribute,
     77 // and MSVC doesn't support any GCC attributes.
     78 # define _LIBCPP_INIT_PRIORITY_MAX
     79 #else
     80 # define _LIBCPP_INIT_PRIORITY_MAX __attribute__((init_priority(101)))
     81 #endif
     82 
     83 // When compiled in C++14 this initialization should be a constant expression.
     84 // Only in C++11 is "init_priority" needed to ensure initialization order.
     85 #if _LIBCPP_STD_VER > 11
     86 _LIBCPP_SAFE_STATIC
     87 #endif
     88 ResourceInitHelper res_init _LIBCPP_INIT_PRIORITY_MAX;
     89 
     90 } // end namespace
     91 
     92 
     93 memory_resource * new_delete_resource() _NOEXCEPT {
     94     return &res_init.resources.new_delete_res;
     95 }
     96 
     97 memory_resource * null_memory_resource() _NOEXCEPT {
     98     return &res_init.resources.null_res;
     99 }
    100 
    101 // default_memory_resource()
    102 
    103 static memory_resource *
    104 __default_memory_resource(bool set = false, memory_resource * new_res = nullptr) _NOEXCEPT
    105 {
    106 #ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
    107     _LIBCPP_SAFE_STATIC static atomic<memory_resource*> __res =
    108         ATOMIC_VAR_INIT(&res_init.resources.new_delete_res);
    109     if (set) {
    110         new_res = new_res ? new_res : new_delete_resource();
    111         // TODO: Can a weaker ordering be used?
    112         return _VSTD::atomic_exchange_explicit(
    113             &__res, new_res, memory_order::memory_order_acq_rel);
    114     }
    115     else {
    116         return _VSTD::atomic_load_explicit(
    117             &__res, memory_order::memory_order_acquire);
    118     }
    119 #elif !defined(_LIBCPP_HAS_NO_THREADS)
    120     _LIBCPP_SAFE_STATIC static memory_resource * res = &res_init.resources.new_delete_res;
    121     static mutex res_lock;
    122     if (set) {
    123         new_res = new_res ? new_res : new_delete_resource();
    124         lock_guard<mutex> guard(res_lock);
    125         memory_resource * old_res = res;
    126         res = new_res;
    127         return old_res;
    128     } else {
    129         lock_guard<mutex> guard(res_lock);
    130         return res;
    131     }
    132 #else
    133     _LIBCPP_SAFE_STATIC static memory_resource* res = &res_init.resources.new_delete_res;
    134     if (set) {
    135         new_res = new_res ? new_res : new_delete_resource();
    136         memory_resource * old_res = res;
    137         res = new_res;
    138         return old_res;
    139     } else {
    140         return res;
    141     }
    142 #endif
    143 }
    144 
    145 memory_resource * get_default_resource() _NOEXCEPT
    146 {
    147     return __default_memory_resource();
    148 }
    149 
    150 memory_resource * set_default_resource(memory_resource * __new_res) _NOEXCEPT
    151 {
    152     return __default_memory_resource(true, __new_res);
    153 }
    154 
    155 _LIBCPP_END_NAMESPACE_LFTS_PMR
    156