text: /*
   * This file is part of PowerDNS or dnsdist.
   * Copyright -- PowerDNS.COM B.V. and its contributors
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of version 2 of the GNU General Public License as
   * published by the Free Software Foundation.
   *
   * In addition, for the avoidance of any doubt, permission is granted to
   * link this program with OpenSSL and to (re)distribute the binaries
   * produced as the result of such linking.
   *
   * This program 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.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
   */
  #pragma once
  #include <cstddef>
  #include <utility>
  #include <type_traits>
  #include <new>
  #include <sys/mman.h>
  
  // On OpenBSD mem used as stack should be marked MAP_STACK
  #if !defined(MAP_STACK)
  #define MAP_STACK 0
  #endif
  
  template <typename T>
  struct lazy_allocator {
      using value_type = T;
      using pointer = T*;
      using size_type = std::size_t;
      static_assert (std::is_trivial<T>::value,
                     "lazy_allocator must only be used with trivial types");
  
      pointer
      allocate (size_type const n) {
  #ifdef __OpenBSD__
          void *p = mmap(nullptr, n * sizeof(value_type),
            PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON | MAP_STACK, -1, 0);
          if (p == MAP_FAILED)
            throw std::bad_alloc();
          return static_cast<pointer>(p);
  #else
          return static_cast<pointer>(::operator new (n * sizeof(value_type)));
  #endif
      }
  
      void
      deallocate (pointer const ptr, size_type const n) noexcept {
  #ifdef __OpenBSD__
          munmap(ptr, n * sizeof(value_type));
  #else
  #if defined(__cpp_sized_deallocation) &&  (__cpp_sized_deallocation >= 201309)
          ::operator delete (ptr, n * sizeof(value_type));
  #else
          (void) n;
          ::operator delete (ptr);
  #endif
  #endif
      }
  
      void construct (T*) const noexcept {}
  
      template <typename X, typename... Args>
      void
      construct (X* place, Args&&... args) const noexcept {
          new (static_cast<void*>(place)) X (std::forward<Args>(args)...);
      }
  };
  
  template <typename T> inline
  bool operator== (lazy_allocator<T> const&, lazy_allocator<T> const&) noexcept {
      return true;
  }
  
  template <typename T> inline
  bool operator!= (lazy_allocator<T> const&, lazy_allocator<T> const&) noexcept {
      return false;
  }
  