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// <memory_resource> implementation -*- C++ -*-
// Copyright (C) 2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
#include <memory_resource>
#include <atomic>
#include <new>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace pmr
{
namespace
{
class newdel_res_t final : public memory_resource
{
void*
do_allocate(size_t __bytes, size_t __alignment) override
{ return ::operator new(__bytes, std::align_val_t(__alignment)); }
void
do_deallocate(void* __p, size_t __bytes, size_t __alignment) noexcept
override
{ ::operator delete(__p, __bytes, std::align_val_t(__alignment)); }
bool
do_is_equal(const memory_resource& __other) const noexcept override
{ return &__other == this; }
};
class null_res_t final : public memory_resource
{
void*
do_allocate(size_t, size_t) override
{ std::__throw_bad_alloc(); }
void
do_deallocate(void*, size_t, size_t) noexcept override
{ }
bool
do_is_equal(const memory_resource& __other) const noexcept override
{ return &__other == this; }
};
template<typename T>
struct constant_init
{
union {
unsigned char unused;
T obj;
};
constexpr constant_init() : obj() { }
template<typename U>
explicit constexpr constant_init(U arg) : obj(arg) { }
~constant_init() { /* do nothing, union member is not destroyed */ }
};
constant_init<newdel_res_t> newdel_res{};
constant_init<null_res_t> null_res{};
constant_init<atomic<memory_resource*>> default_res{&newdel_res.obj};
} // namespace
memory_resource*
new_delete_resource() noexcept
{ return &newdel_res.obj; }
memory_resource*
null_memory_resource() noexcept
{ return &null_res.obj; }
memory_resource*
set_default_resource(memory_resource* r) noexcept
{
if (r == nullptr)
r = new_delete_resource();
return default_res.obj.exchange(r);
}
memory_resource*
get_default_resource() noexcept
{ return default_res.obj.load(); }
// Member functions for std::pmr::monotonic_buffer_resource
// Memory allocated by the upstream resource is managed in a linked list
// of _Chunk objects. A _Chunk object recording the size and alignment of
// the allocated block and a pointer to the previous chunk is placed
// at end of the block.
class monotonic_buffer_resource::_Chunk
{
public:
// Return the address and size of a block of memory allocated from __r,
// of at least __size bytes and aligned to __align.
// Add a new _Chunk to the front of the linked list at __head.
static pair<void*, size_t>
allocate(memory_resource* __r, size_t __size, size_t __align,
_Chunk*& __head)
{
__size = std::__ceil2(__size + sizeof(_Chunk));
void* __p = __r->allocate(__size, __align);
// Add a chunk defined by (__p, __size, __align) to linked list __head.
void* const __back = (char*)__p + __size - sizeof(_Chunk);
__head = ::new(__back) _Chunk(__size, __align, __head);
return { __p, __size - sizeof(_Chunk) };
}
// Return every chunk in linked list __head to resource __r.
static void
release(_Chunk*& __head, memory_resource* __r) noexcept
{
_Chunk* __next = __head;
__head = nullptr;
while (__next)
{
_Chunk* __ch = __next;
__builtin_memcpy(&__next, __ch->_M_next, sizeof(_Chunk*));
__glibcxx_assert(__ch->_M_canary != 0);
__glibcxx_assert(__ch->_M_canary == (__ch->_M_size|__ch->_M_align));
if (__ch->_M_canary != (__ch->_M_size | __ch->_M_align))
return; // buffer overflow detected!
size_t __size = (1u << __ch->_M_size);
size_t __align = (1u << __ch->_M_align);
void* __start = (char*)(__ch + 1) - __size;
__r->deallocate(__start, __size, __align);
}
}
private:
_Chunk(size_t __size, size_t __align, _Chunk* __next) noexcept
: _M_size(std::__log2p1(__size) - 1),
_M_align(std::__log2p1(__align) - 1)
{
__builtin_memcpy(_M_next, &__next, sizeof(__next));
_M_canary = _M_size | _M_align;
}
unsigned char _M_canary;
unsigned char _M_size;
unsigned char _M_align;
unsigned char _M_next[sizeof(_Chunk*)];
};
void
monotonic_buffer_resource::_M_new_buffer(size_t bytes, size_t alignment)
{
// Need to check this somewhere, so put it here:
static_assert(alignof(monotonic_buffer_resource::_Chunk) == 1);
const size_t n = std::max(bytes, _M_next_bufsiz);
const size_t m = std::max(alignment, alignof(std::max_align_t));
auto [p, size] = _Chunk::allocate(_M_upstream, n, m, _M_head);
_M_current_buf = p;
_M_avail = size;
_M_next_bufsiz *= _S_growth_factor;
}
void
monotonic_buffer_resource::_M_release_buffers() noexcept
{
_Chunk::release(_M_head, _M_upstream);
}
} // namespace pmr
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
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