3 files changed, 181 insertions, 0 deletions
diff --git a/src/buildtool/storage/TARGETS b/src/buildtool/storage/TARGETS
index 71e0de6a..1cd5fed9 100644
--- a/src/buildtool/storage/TARGETS
+++ b/src/buildtool/storage/TARGETS
@@ -18,6 +18,19 @@
     ]
   , "stage": ["src", "buildtool", "storage"]
   }
+, "repository_garbage_collector":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["repository_garbage_collector"]
+  , "hdrs": ["repository_garbage_collector.hpp"]
+  , "srcs": ["repository_garbage_collector.cpp"]
+  , "deps": ["config", ["src/utils/cpp", "file_locking"]]
+  , "private-deps":
+    [ ["src/buildtool/execution_api/common", "common"]
+    , ["src/buildtool/file_system", "file_system_manager"]
+    , ["src/buildtool/logging", "logging"]
+    ]
+  , "stage": ["src", "buildtool", "storage"]
+  }
 , "storage":
   { "type": ["@", "rules", "CC", "library"]
   , "name": ["storage"]
diff --git a/src/buildtool/storage/repository_garbage_collector.cpp b/src/buildtool/storage/repository_garbage_collector.cpp
new file mode 100644
index 00000000..f1025795
--- /dev/null
+++ b/src/buildtool/storage/repository_garbage_collector.cpp
@@ -0,0 +1,119 @@
+// Copyright 2024 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/buildtool/storage/repository_garbage_collector.hpp"
+
+#include "src/buildtool/execution_api/common/execution_common.hpp"
+#include "src/buildtool/file_system/file_system_manager.hpp"
+#include "src/buildtool/logging/log_level.hpp"
+#include "src/buildtool/logging/logger.hpp"
+
+auto RepositoryGarbageCollector::SharedLock(
+    StorageConfig const& storage_config) noexcept -> std::optional<LockFile> {
+    return LockFile::Acquire(LockFilePath(storage_config), /*is_shared=*/true);
+}
+
+auto RepositoryGarbageCollector::ExclusiveLock(
+    StorageConfig const& storage_config) noexcept -> std::optional<LockFile> {
+    return LockFile::Acquire(LockFilePath(storage_config), /*is_shared=*/false);
+}
+
+auto RepositoryGarbageCollector::LockFilePath(
+    StorageConfig const& storage_config) noexcept -> std::filesystem::path {
+    return storage_config.RepositoryRoot() / "gc.lock";
+}
+
+auto RepositoryGarbageCollector::TriggerGarbageCollection(
+    StorageConfig const& storage_config) noexcept -> bool {
+    auto const kRemoveMe = std::string{"remove-me"};
+
+    auto pid = CreateProcessUniqueId();
+    if (not pid) {
+        return false;
+    }
+    auto remove_me = storage_config.RepositoryRoot() / (kRemoveMe + *pid);
+
+    // With a shared lock, we can remove that directory, if it exists,
+    // as we own the process id.
+    {
+        auto lock = SharedLock(storage_config);
+        if (not lock) {
+            Logger::Log(LogLevel::Error,
+                        "Failed to get a shared lock the for repository root");
+            return false;
+        }
+        if (FileSystemManager::IsDirectory(remove_me)) {
+            if (not FileSystemManager::RemoveDirectory(remove_me)) {
+                Logger::Log(LogLevel::Error,
+                            "Failed to remove directory {}",
+                            remove_me.string());
+                return false;
+            }
+        }
+        else {
+            if (not FileSystemManager::RemoveFile(remove_me)) {
+                Logger::Log(
+                    LogLevel::Error, "Failed to remove {}", remove_me.string());
+                return false;
+            }
+        }
+    }
+
+    // after releasing the shared lock, wait to get an exclusive lock for doing
+    // the critical renaming
+    {
+        auto lock = ExclusiveLock(storage_config);
+        if (not lock) {
+            Logger::Log(LogLevel::Error,
+                        "Failed to exclusively lock the local repository root");
+            return false;
+        }
+
+        for (std::size_t i = storage_config.num_generations; i > 0; i--) {
+            auto from = storage_config.RepositoryGenerationRoot(i - 1);
+            auto to = i < storage_config.num_generations
+                          ? storage_config.RepositoryGenerationRoot(i)
+                          : remove_me;
+            if (FileSystemManager::IsDirectory(from)) {
+                if (not FileSystemManager::Rename(from, to)) {
+                    Logger::Log(LogLevel::Error,
+                                "Failed to rename {} to {}",
+                                from.string(),
+                                to.string());
+                    return false;
+                }
+            }
+        }
+    }
+
+    // Finally, with a shared lock, clean up the directory to be removed
+    {
+        auto lock = SharedLock(storage_config);
+        if (not lock) {
+            Logger::Log(LogLevel::Error,
+                        "Failed to get a shared lock for the repository root");
+            return false;
+        }
+        if (FileSystemManager::IsDirectory(remove_me)) {
+            if (not FileSystemManager::RemoveDirectory(remove_me)) {
+                Logger::Log(LogLevel::Error,
+                            "Failed to remove directory {}",
+                            remove_me.string());
+                return false;
+            }
+        }
+    }
+
+    return true;
+}
diff --git a/src/buildtool/storage/repository_garbage_collector.hpp b/src/buildtool/storage/repository_garbage_collector.hpp
new file mode 100644
index 00000000..1bb3867a
--- /dev/null
+++ b/src/buildtool/storage/repository_garbage_collector.hpp
@@ -0,0 +1,49 @@
+// Copyright 2024 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_BUILDTOOL_STORAGE_REPOSITORY_GARBAGE_COLLECTOR_HPP
+#define INCLUDED_SRC_BUILDTOOL_STORAGE_REPOSITORY_GARBAGE_COLLECTOR_HPP
+
+#include <filesystem>
+#include <optional>
+
+#include "src/buildtool/storage/config.hpp"
+#include "src/utils/cpp/file_locking.hpp"
+
+/// \brief Global garbage collector implementation.
+/// Responsible for deleting oldest generation.
+class RepositoryGarbageCollector {
+  public:
+    /// \brief Trigger garbage collection, i.e., rotate the generations and
+    /// delete the oldest. \returns true on success.
+    [[nodiscard]] auto static TriggerGarbageCollection(
+        StorageConfig const& storage_config) noexcept -> bool;
+
+    /// \brief Acquire shared lock to prevent garbage collection from running.
+    /// \param storage_config   Storage to be locked.
+    /// \returns The acquired lock file on success or nullopt otherwise.
+    [[nodiscard]] auto static SharedLock(
+        StorageConfig const& storage_config) noexcept
+        -> std::optional<LockFile>;
+
+  private:
+    [[nodiscard]] auto static ExclusiveLock(
+        StorageConfig const& storage_config) noexcept
+        -> std::optional<LockFile>;
+
+    [[nodiscard]] auto static LockFilePath(
+        StorageConfig const& storage_config) noexcept -> std::filesystem::path;
+};
+
+#endif  // INCLUDED_SRC_BUILDTOOL_STORAGE_GARBAGE_COLLECTOR_HPP