3 files changed, 190 insertions, 0 deletions
diff --git a/src/utils/cpp/TARGETS b/src/utils/cpp/TARGETS
index c3c513e2..b835023f 100644
--- a/src/utils/cpp/TARGETS
+++ b/src/utils/cpp/TARGETS
@@ -89,4 +89,16 @@
   , "private-deps":
     [["src/buildtool/file_system", "file_system_manager"], ["", "libarchive"]]
   }
+, "file_locking":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["file_locking"]
+  , "hdrs": ["file_locking.hpp"]
+  , "srcs": ["file_locking.cpp"]
+  , "deps": [["@", "gsl-lite", "", "gsl-lite"]]
+  , "stage": ["src", "utils", "cpp"]
+  , "private-deps":
+    [ ["src/buildtool/file_system", "file_system_manager"]
+    , ["src/utils/cpp", "path"]
+    ]
+  }
 }
diff --git a/src/utils/cpp/file_locking.cpp b/src/utils/cpp/file_locking.cpp
new file mode 100644
index 00000000..3868af1b
--- /dev/null
+++ b/src/utils/cpp/file_locking.cpp
@@ -0,0 +1,113 @@
+// 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.
+
+#include "src/utils/cpp/file_locking.hpp"
+
+#include <sys/file.h>
+
+#include "src/buildtool/file_system/file_system_manager.hpp"
+#include "src/utils/cpp/path.hpp"
+
+auto LockFile::Acquire(std::filesystem::path const& fspath,
+                       bool is_shared) noexcept -> std::optional<LockFile> {
+    static std::mutex lock_mutex{};
+    try {
+        // ensure thread-safety
+        std::unique_lock lock{lock_mutex};
+        // get path to lock file
+        auto lock_file = GetLockFilePath(fspath);
+        if (not lock_file) {
+            return std::nullopt;
+        }
+        // touch lock file
+        if (not FileSystemManager::CreateFile(*lock_file)) {
+            Logger::Log(LogLevel::Error,
+                        "LockFile: could not create file {}",
+                        lock_file->string());
+            return std::nullopt;
+        }
+        // get open file descriptor
+        gsl::owner<FILE*> file_handle = std::fopen(lock_file->c_str(), "r");
+        if (file_handle == nullptr) {
+            Logger::Log(LogLevel::Error,
+                        "LockFile: could not open descriptor for file {}",
+                        lock_file->string());
+            return std::nullopt;
+        }
+        // attach flock
+        auto err = flock(fileno(file_handle), is_shared ? LOCK_SH : LOCK_EX);
+        if (err != 0) {
+            Logger::Log(
+                LogLevel::Error,
+                "LockFile: applying lock to file {} failed with errno {}",
+                lock_file->string(),
+                errno);
+            fclose(file_handle);
+            return std::nullopt;
+        }
+        // lock file has been acquired
+        return LockFile(file_handle, *lock_file);
+    } catch (std::exception const& ex) {
+        Logger::Log(
+            LogLevel::Error,
+            "LockFile: acquiring file lock for path {} failed with:\n{}",
+            fspath.string(),
+            ex.what());
+        return std::nullopt;
+    }
+}
+
+LockFile::~LockFile() noexcept {
+    if (file_handle_ != nullptr) {
+        // close open file descriptor
+        fclose(file_handle_);
+        file_handle_ = nullptr;
+    }
+}
+
+auto LockFile::GetLockFilePath(std::filesystem::path const& fspath) noexcept
+    -> std::optional<std::filesystem::path> {
+    try {
+        // bring to normal form
+        auto abs_fspath = ToNormalPath(std::filesystem::absolute(fspath));
+        auto filename = abs_fspath.filename();
+        auto parent = abs_fspath.parent_path();
+        // create parent folder
+        if (not FileSystemManager::CreateDirectory(parent)) {
+            return std::nullopt;
+        }
+        // get lock file name
+        return parent / filename;
+    } catch (std::exception const& ex) {
+        Logger::Log(
+            LogLevel::Error,
+            "LockFile: defining lock file name for path {} failed with:\n{}",
+            fspath.string(),
+            ex.what());
+        return std::nullopt;
+    }
+}
+
+LockFile::LockFile(LockFile&& other) noexcept
+    : file_handle_{other.file_handle_},
+      lock_file_{std::move(other.lock_file_)} {
+    other.file_handle_ = nullptr;
+}
+
+auto LockFile::operator=(LockFile&& other) noexcept -> LockFile& {
+    file_handle_ = other.file_handle_;
+    other.file_handle_ = nullptr;
+    lock_file_ = std::move(other.lock_file_);
+    return *this;
+}
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