pdns/lazy_allocator.hh

   1 /*
   2  * This file is part of PowerDNS or dnsdist.
   3  * Copyright -- PowerDNS.COM B.V. and its contributors
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of version 2 of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * In addition, for the avoidance of any doubt, permission is granted to
  10  * link this program with OpenSSL and to (re)distribute the binaries
  11  * produced as the result of such linking.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  */
  22 #ifndef LAZY_ALLOCATOR_HH
  23 #define LAZY_ALLOCATOR_HH
  24
  25 #include <cstddef>
  26 #include <utility>
  27 #include <type_traits>
  28 #include <new>
  29 #include <sys/mman.h>
  30
  31 // On OpenBSD mem used as stack should be marked MAP_STACK
  32 #if !defined(MAP_STACK)
  33 #define MAP_STACK 0
  34 #endif
  35
  36 template <typename T>
  37 struct lazy_allocator {
  38     using value_type = T;
  39     using pointer = T*;
  40     using size_type = std::size_t;
  41     static_assert (std::is_trivial<T>::value,
  42                    "lazy_allocator must only be used with trivial types");
  43
  44     pointer
  45     allocate (size_type const n) {
  46         void *p = mmap(nullptr, n * sizeof(value_type),
  47           PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON | MAP_STACK, -1, 0);
  48         if (p == MAP_FAILED)
  49           throw std::bad_alloc();
  50         return static_cast<pointer>(p);
  51     }
  52
  53     void
  54     deallocate (pointer const ptr, size_type const n) noexcept {
  55         munmap(ptr, n * sizeof(value_type));
  56     }
  57
  58     void construct (T*) const noexcept {}
  59
  60     template <typename X, typename... Args>
  61     void
  62     construct (X* place, Args&&... args) const noexcept {
  63         new (static_cast<void*>(place)) X (std::forward<Args>(args)...);
  64     }
  65 };
  66
  67 template <typename T> inline
  68 bool operator== (lazy_allocator<T> const&, lazy_allocator<T> const&) noexcept {
  69     return true;
  70 }
  71
  72 template <typename T> inline
  73 bool operator!= (lazy_allocator<T> const&, lazy_allocator<T> const&) noexcept {
  74     return false;
  75 }
  76
  77 #endif // LAZY_ALLOCATOR_HH