memory_promise.h

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#pragma once
 
#include "../../pmr/memory_resource.h"
#include "../../pmr/throw_bad_alloc.h"
 
namespace emlabcpp::coro
{
 
template < typename PromiseType >
struct memory_promise
{
        static constexpr std::size_t ptr_size = sizeof( pmr::memory_resource* );
 
        void*
        operator new( std::size_t const sz, auto&, pmr::memory_resource& pi, auto&&... ) noexcept
        {
                return alloc( sz, pi );
        }
 
        void* operator new( std::size_t const sz, pmr::memory_resource& pi, auto&&... ) noexcept
        {
                return alloc( sz, pi );
        }
 
        void* operator new( std::size_t const sz, auto&&... ) noexcept = delete;
 
        static void* alloc( std::size_t sz, pmr::memory_resource& pi )
        {
                sz += ptr_size;
                void* const vp = pi.allocate( sz, alignof( PromiseType ) );
 
                auto p = reinterpret_cast< pmr::memory_resource** >( vp );
 
                *p = &pi;
 
                p++;
 
                return static_cast< void* >( p );
        }
 
        void operator delete( void* const ptr, std::size_t const size )
        {
                auto p = reinterpret_cast< pmr::memory_resource** >( ptr );
 
                p--;
 
                bool const res = ( *p )->deallocate(
                    static_cast< void* >( p ), size + ptr_size, alignof( PromiseType ) );
                if ( !res )
                        pmr::throw_bad_alloc();
        }
};
}  // namespace emlabcpp::coro