src/experimental/memory_resource.cpp

//===------------------------ memory_resource.cpp -------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "experimental/memory_resource"

#ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
#include "atomic"
#elif !defined(_LIBCPP_HAS_NO_THREADS)
#include "mutex"
#endif

_LIBCPP_BEGIN_NAMESPACE_LFTS_PMR

// memory_resource

//memory_resource::~memory_resource() {}

// new_delete_resource()

class _LIBCPP_TYPE_VIS_ONLY __new_delete_memory_resource_imp
    : public memory_resource
{
public:
    ~__new_delete_memory_resource_imp() = default;

protected:
    virtual void* do_allocate(size_t __size, size_t __align)
        { return __allocate(__size); }

    virtual void do_deallocate(void * __p, size_t, size_t)
        { __deallocate(__p); }

    virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
        { return &__other == this; }
};

// null_memory_resource()

class _LIBCPP_TYPE_VIS_ONLY __null_memory_resource_imp
    : public memory_resource
{
public:
    ~__null_memory_resource_imp() = default;

protected:
    virtual void* do_allocate(size_t, size_t) {
        __throw_bad_alloc();
    }
    virtual void do_deallocate(void *, size_t, size_t) {}
    virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
    { return &__other == this; }
};

namespace {

union ResourceInitHelper {
  struct {
    __new_delete_memory_resource_imp new_delete_res;
    __null_memory_resource_imp       null_res;
  } resources;
  char dummy;
  _LIBCPP_CONSTEXPR_AFTER_CXX11 ResourceInitHelper() : resources() {}
  ~ResourceInitHelper() {}
};
// When compiled in C++14 this initialization should be a constant expression.
// Only in C++11 is "init_priority" needed to ensure initialization order.
ResourceInitHelper res_init __attribute__((init_priority (101)));

} // end namespace


memory_resource * new_delete_resource() _NOEXCEPT {
    return &res_init.resources.new_delete_res;
}

memory_resource * null_memory_resource() _NOEXCEPT {
    return &res_init.resources.null_res;
}

// default_memory_resource()

static memory_resource *
__default_memory_resource(bool set = false, memory_resource * new_res = nullptr) _NOEXCEPT
{
#ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
    static atomic<memory_resource*> __res =
        ATOMIC_VAR_INIT(&res_init.resources.new_delete_res);
    if (set) {
        new_res = new_res ? new_res : new_delete_resource();
        // TODO: Can a weaker ordering be used?
        return _VSTD::atomic_exchange_explicit(
            &__res, new_res, memory_order::memory_order_acq_rel);
    }
    else {
        return _VSTD::atomic_load_explicit(
            &__res, memory_order::memory_order_acquire);
    }
#elif !defined(_LIBCPP_HAS_NO_THREADS)
    static memory_resource * res = &res_init.resources.new_delete_res;
    static mutex res_lock;
    if (set) {
        new_res = new_res ? new_res : new_delete_resource();
        lock_guard<mutex> guard(res_lock);
        memory_resource * old_res = res;
        res = new_res;
        return old_res;
    } else {
        lock_guard<mutex> guard(res_lock);
        return res;
    }
#else
    static memory_resource* res = &res_init.resources.new_delete_res;
    if (set) {
        new_res = new_res ? new_res : new_delete_resource();
        memory_resource * old_res = res;
        res = new_res;
        return old_res;
    } else {
        return res;
    }
#endif
}

memory_resource * get_default_resource() _NOEXCEPT
{
    return __default_memory_resource();
}

memory_resource * set_default_resource(memory_resource * __new_res) _NOEXCEPT
{
    return __default_memory_resource(true, __new_res);
}

_LIBCPP_END_NAMESPACE_LFTS_PMR