ceph/src/seastar/include/seastar/core/transfer.hh

   1 /*
   2  * This file is open source software, licensed to you under the terms
   3  * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
   4  * distributed with this work for additional information regarding copyright
   5  * ownership.  You may not use this file except in compliance with the License.
   6  *
   7  * You may obtain a copy of the License at
   8  *
   9  *   http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing,
  12  * software distributed under the License is distributed on an
  13  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14  * KIND, either express or implied.  See the License for the
  15  * specific language governing permissions and limitations
  16  * under the License.
  17  */
  18 /*
  19  * Copyright (C) 2014 Cloudius Systems, Ltd.
  20  */
  21
  22 #pragma once
  23
  24 // Helper functions for copying or moving multiple objects in an exception
  25 // safe manner, then destroying the sources.
  26 //
  27 // To transfer, call transfer_pass1(allocator, &from, &to) on all object pairs,
  28 // (this copies the object from @from to @to).  If no exceptions are encountered,
  29 // call transfer_pass2(allocator, &from, &to).  This destroys the object at the
  30 // origin.  If exceptions were encountered, simply destroy all copied objects.
  31 //
  32 // As an optimization, if the objects are moveable without throwing (noexcept)
  33 // transfer_pass1() simply moves the objects and destroys the source, and
  34 // transfer_pass2() does nothing.
  35
  36 #include <type_traits>
  37 #include <utility>
  38
  39 namespace seastar {
  40
  41 template <typename T, typename Alloc>
  42 inline
  43 void
  44 transfer_pass1(Alloc& a, T* from, T* to,
  45         typename std::enable_if<std::is_nothrow_move_constructible<T>::value>::type* = nullptr) {
  46     a.construct(to, std::move(*from));
  47     a.destroy(from);
  48 }
  49
  50 template <typename T, typename Alloc>
  51 inline
  52 void
  53 transfer_pass2(Alloc& a, T* from, T* to,
  54         typename std::enable_if<std::is_nothrow_move_constructible<T>::value>::type* = nullptr) {
  55 }
  56
  57 template <typename T, typename Alloc>
  58 inline
  59 void
  60 transfer_pass1(Alloc& a, T* from, T* to,
  61         typename std::enable_if<!std::is_nothrow_move_constructible<T>::value>::type* = nullptr) {
  62     a.construct(to, *from);
  63 }
  64
  65 template <typename T, typename Alloc>
  66 inline
  67 void
  68 transfer_pass2(Alloc& a, T* from, T* to,
  69         typename std::enable_if<!std::is_nothrow_move_constructible<T>::value>::type* = nullptr) {
  70     a.destroy(from);
  71 }
  72
  73 }
  74