ceph/src/seastar/include/seastar/util/defer.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 #include <type_traits>
  25 #include <utility>
  26
  27 #include <seastar/util/concepts.hh>
  28
  29 #ifdef SEASTAR_DEFERRED_ACTION_REQUIRE_NOEXCEPT
  30 #define SEASTAR_DEFERRED_ACTION_NOEXCEPT noexcept
  31 #else
  32 #define SEASTAR_DEFERRED_ACTION_NOEXCEPT
  33 #endif
  34
  35 SEASTAR_CONCEPT(
  36 template <typename Func>
  37 concept deferrable_action = requires (Func func) {
  38     { func() } SEASTAR_DEFERRED_ACTION_NOEXCEPT -> std::same_as<void>;
  39 };
  40 )
  41
  42 namespace seastar {
  43
  44 template <typename Func>
  45 SEASTAR_CONCEPT( requires deferrable_action<Func> )
  46 class [[nodiscard("unassigned deferred_action")]] deferred_action {
  47     Func _func;
  48     bool _cancelled = false;
  49 public:
  50     static_assert(std::is_nothrow_move_constructible<Func>::value, "Func(Func&&) must be noexcept");
  51     deferred_action(Func&& func) noexcept : _func(std::move(func)) {}
  52     deferred_action(deferred_action&& o) noexcept : _func(std::move(o._func)), _cancelled(o._cancelled) {
  53         o._cancelled = true;
  54     }
  55     deferred_action& operator=(deferred_action&& o) noexcept {
  56         if (this != &o) {
  57             this->~deferred_action();
  58             new (this) deferred_action(std::move(o));
  59         }
  60         return *this;
  61     }
  62     deferred_action(const deferred_action&) = delete;
  63     ~deferred_action() { if (!_cancelled) { _func(); }; }
  64     void cancel() { _cancelled = true; }
  65 };
  66
  67 template <typename Func>
  68 SEASTAR_CONCEPT( requires deferrable_action<Func> )
  69 inline
  70 deferred_action<Func>
  71 defer(Func&& func) {
  72     return deferred_action<Func>(std::forward<Func>(func));
  73 }
  74
  75 }