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// Copyright 2021 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_CLEANUP_INTERNAL_CLEANUP_H_
#define ABSL_CLEANUP_INTERNAL_CLEANUP_H_
#include <new>
#include <type_traits>
#include <utility>
#include "absl/base/macros.h"
#include "absl/base/thread_annotations.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace cleanup_internal {
struct Tag {};
template <typename Arg, typename... Args>
constexpr bool WasDeduced() {
return (std::is_same<cleanup_internal::Tag, Arg>::value) &&
(sizeof...(Args) == 0);
}
template <typename Callback>
constexpr bool ReturnsVoid() {
return (std::is_same<std::invoke_result_t<Callback>, void>::value);
}
template <typename Callback>
class Storage {
public:
Storage() = delete;
explicit Storage(Callback callback) {
// Placement-new into a character buffer is used for eager destruction when
// the cleanup is invoked or cancelled. To ensure this optimizes well, the
// behavior is implemented locally instead of using an absl::optional.
::new (GetCallbackBuffer()) Callback(std::move(callback));
is_callback_engaged_ = true;
}
Storage(Storage&& other) {
ABSL_HARDENING_ASSERT(other.IsCallbackEngaged());
::new (GetCallbackBuffer()) Callback(std::move(other.GetCallback()));
is_callback_engaged_ = true;
other.DestroyCallback();
}
Storage(const Storage& other) = delete;
Storage& operator=(Storage&& other) = delete;
Storage& operator=(const Storage& other) = delete;
void* GetCallbackBuffer() { return static_cast<void*>(callback_buffer_); }
Callback& GetCallback() {
return *reinterpret_cast<Callback*>(GetCallbackBuffer());
}
bool IsCallbackEngaged() const { return is_callback_engaged_; }
void DestroyCallback() {
is_callback_engaged_ = false;
GetCallback().~Callback();
}
void InvokeCallback() ABSL_NO_THREAD_SAFETY_ANALYSIS {
std::move(GetCallback())();
}
private:
bool is_callback_engaged_;
alignas(Callback) unsigned char callback_buffer_[sizeof(Callback)];
};
} // namespace cleanup_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_CLEANUP_INTERNAL_CLEANUP_H_
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