From 33812e4986bc03e42e3d61cc008cae301a6ddf89 Mon Sep 17 00:00:00 2001
From: Paul Cristian Sarbu <paul.cristian.sarbu@huawei.com>
Date: Thu, 17 Nov 2022 10:18:15 +0100
Subject: Utils: Add file locking utility class

---
 src/utils/cpp/file_locking.hpp | 65 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 src/utils/cpp/file_locking.hpp

(limited to 'src/utils/cpp/file_locking.hpp')

diff --git a/src/utils/cpp/file_locking.hpp b/src/utils/cpp/file_locking.hpp
new file mode 100644
index 00000000..a92b874a
--- /dev/null
+++ b/src/utils/cpp/file_locking.hpp
@@ -0,0 +1,65 @@
+// 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 "gsl-lite/gsl-lite.hpp"
+
+/* \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.
+ * Lock path and name conventions: a/b.c, a/b/, a/b => a/b.lock; / => /.lock;
+ */
+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 in the given directory path.
+    /// 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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