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//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//
#ifndef BOOST_BEAST_EXAMPLE_FIELDS_ALLOC_HPP
#define BOOST_BEAST_EXAMPLE_FIELDS_ALLOC_HPP
#include <boost/throw_exception.hpp>
#include <cstdlib>
#include <memory>
#include <stdexcept>
namespace detail {
struct static_pool
{
std::size_t size_;
std::size_t refs_ = 1;
std::size_t count_ = 0;
char* p_;
char*
end()
{
return reinterpret_cast<char*>(this + 1) + size_;
}
explicit
static_pool(std::size_t size)
: size_(size)
, p_(reinterpret_cast<char*>(this + 1))
{
}
public:
static
static_pool&
construct(std::size_t size)
{
auto p = new char[sizeof(static_pool) + size];
return *(::new(p) static_pool{size});
}
static_pool&
share()
{
++refs_;
return *this;
}
void
destroy()
{
if(--refs_)
return;
this->~static_pool();
delete[] reinterpret_cast<char*>(this);
}
void*
alloc(std::size_t n)
{
auto last = p_ + n;
if(last >= end())
BOOST_THROW_EXCEPTION(std::bad_alloc{});
++count_;
auto p = p_;
p_ = last;
return p;
}
void
dealloc()
{
if(--count_)
return;
p_ = reinterpret_cast<char*>(this + 1);
}
};
} // detail
/** A non-thread-safe allocator optimized for @ref basic_fields.
This allocator obtains memory from a pre-allocated memory block
of a given size. It does nothing in deallocate until all
previously allocated blocks are deallocated, upon which it
resets the internal memory block for re-use.
To use this allocator declare an instance persistent to the
connection or session, and construct with the block size.
A good rule of thumb is 20% more than the maximum allowed
header size. For example if the application only allows up
to an 8,000 byte header, the block size could be 9,600.
Then, for every instance of `message` construct the header
with a copy of the previously declared allocator instance.
*/
template<class T>
struct fields_alloc
{
detail::static_pool* pool_;
public:
using value_type = T;
using is_always_equal = std::false_type;
using pointer = T*;
using reference = T&;
using const_pointer = T const*;
using const_reference = T const&;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
template<class U>
struct rebind
{
using other = fields_alloc<U>;
};
#if defined(_GLIBCXX_USE_CXX11_ABI) && (_GLIBCXX_USE_CXX11_ABI == 0)
// Workaround for g++
// basic_string assumes that allocators are default-constructible
// See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56437
fields_alloc() = default;
#endif
explicit
fields_alloc(std::size_t size)
: pool_(&detail::static_pool::construct(size))
{
}
fields_alloc(fields_alloc const& other)
: pool_(&other.pool_->share())
{
}
template<class U>
fields_alloc(fields_alloc<U> const& other)
: pool_(&other.pool_->share())
{
}
~fields_alloc()
{
pool_->destroy();
}
value_type*
allocate(size_type n)
{
return static_cast<value_type*>(
pool_->alloc(n * sizeof(T)));
}
void
deallocate(value_type*, size_type)
{
pool_->dealloc();
}
#if defined(BOOST_LIBSTDCXX_VERSION) && BOOST_LIBSTDCXX_VERSION < 60000
template<class U, class... Args>
void
construct(U* ptr, Args&&... args)
{
::new(static_cast<void*>(ptr)) U(
std::forward<Args>(args)...);
}
template<class U>
void
destroy(U* ptr)
{
ptr->~U();
}
#endif
template<class U>
friend
bool
operator==(
fields_alloc const& lhs,
fields_alloc<U> const& rhs)
{
return &lhs.pool_ == &rhs.pool_;
}
template<class U>
friend
bool
operator!=(
fields_alloc const& lhs,
fields_alloc<U> const& rhs)
{
return ! (lhs == rhs);
}
};
#endif
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