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// Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
//
// 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
//
// http://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 INCLUDED_SRC_OTHER_TOOLS_FILE_LOCKING_HPP
#define INCLUDED_SRC_OTHER_TOOLS_FILE_LOCKING_HPP
#include <filesystem>
#include <memory>
#include <optional>
#include <utility> // std::move
#include "gsl/gsl"
/* \brief Thread- and process-safe file locking mechanism for paths.
* User guarantees write access in the parent directory of the path given, as
* the lock will be placed there and missing tree directories will be created.
*/
class LockFile {
public:
// no default ctor
LockFile() = delete;
/// \brief Destroy the LockFile object.
/// It only closes the open file descriptor, but does not explicitly unlock.
~LockFile() noexcept;
// no copies, only moves
LockFile(LockFile const&) = delete;
LockFile(LockFile&& other) noexcept;
auto operator=(LockFile const&) = delete;
auto operator=(LockFile&& other) noexcept -> LockFile&;
/// \brief Tries to acquire a lock file with the given name.
/// Missing directories will be created if write permission exists.
/// Returns the lock file object on success, nullopt on failure.
[[nodiscard]] static auto Acquire(std::filesystem::path const& fspath,
bool is_shared) noexcept
-> std::optional<LockFile>;
private:
gsl::owner<FILE*> file_handle_{nullptr};
std::filesystem::path lock_file_{};
/// \brief Private ctor. Instances are only created by Acquire method.
explicit LockFile(gsl::owner<FILE*> file_handle,
std::filesystem::path lock_file) noexcept
: file_handle_{file_handle}, lock_file_{std::move(lock_file)} {};
[[nodiscard]] static auto GetLockFilePath(
std::filesystem::path const& fspath) noexcept
-> std::optional<std::filesystem::path>;
};
#endif // FILE_LOCKING
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