feat: add Shutdown method to IDataSystem

libs/server-sdk/src/client_impl.cpp

@@ -440,6 +440,7 @@ IDataSourceStatusProvider& ClientImpl::DataSourceStatus() {
 // }
 
 ClientImpl::~ClientImpl() {
+    data_system_->Shutdown(); // This is a blocking call.
     ioc_.stop();
     // TODO(SC-219101)
     run_thread_.join();

libs/server-sdk/src/data_interfaces/system/idata_system.hpp

@@ -5,29 +5,35 @@
 namespace launchdarkly::server_side::data_interfaces {
 
 /**
- * \brief IDataSystem obtains data used for flag evaluations and makes it available
+ * @brief IDataSystem obtains data used for flag evaluations and makes it available
  * to other components.
  */
 class IDataSystem : public IStore {
-   public:
+public:
     /**
-     * \return Identity of the system. Used in logs.
+     * @return Identity of the system. Used in logs.
      */
     [[nodiscard]] virtual std::string const& Identity() const = 0;
 
     /**
-     * \brief Initializes the system. This method will be called before any of
+     * @brief Initializes the system. This method will be called before any of
      * the IStore methods are called.
      */
     virtual void Initialize() = 0;
 
+    /**
+     * @brief Shuts down the system. This method will be called at some point
+     * after Initialize, after which no methods from IStore will be called.
+     */
+    virtual void Shutdown() = 0;
+
     virtual ~IDataSystem() override = default;
     IDataSystem(IDataSystem const& item) = delete;
     IDataSystem(IDataSystem&& item) = delete;
     IDataSystem& operator=(IDataSystem const&) = delete;
     IDataSystem& operator=(IDataSystem&&) = delete;
 
-   protected:
+protected:
     IDataSystem() = default;
 };
 

libs/server-sdk/src/data_systems/background_sync/background_sync_system.cpp

@@ -47,6 +47,13 @@ void BackgroundSync::Initialize() {
                               nullptr /* no bootstrap data supported yet */);
 }
 
+void BackgroundSync::Shutdown() {
+    auto promise = std::make_shared<std::promise<void>>();
+    auto const did_shutdown = promise->get_future();
+    synchronizer_->ShutdownAsync([promise]() { promise->set_value(); });
+    did_shutdown.wait();
+}
+
 std::string const& BackgroundSync::Identity() const {
     static std::string id = "background sync via " + synchronizer_->Identity();
     return id;

libs/server-sdk/src/data_systems/background_sync/background_sync_system.hpp

@@ -59,6 +59,8 @@ class BackgroundSync final : public data_interfaces::IDataSystem {
 
     void Initialize() override;
 
+    void Shutdown() override;
+
    private:
     data_components::MemoryStore store_;
     data_components::ChangeNotifier change_notifier_;

libs/server-sdk/src/data_systems/lazy_load/lazy_load_system.cpp

@@ -16,6 +16,8 @@ std::string const& LazyLoad::Identity() const {
 
 void LazyLoad::Initialize() {}
 
+void LazyLoad::Shutdown() {}
+
 std::shared_ptr<data_model::FlagDescriptor> LazyLoad::GetFlag(
     std::string const& key) const {
     auto const state = tracker_.State(Keys::kAllSegments, time_());

libs/server-sdk/src/data_systems/lazy_load/lazy_load_system.hpp

@@ -44,6 +44,8 @@ class LazyLoad final : public data_interfaces::IDataSystem {
 
     void Initialize() override;
 
+    void Shutdown() override;
+
    private:
     void RefreshAllFlags() const;
     void RefreshAllSegments() const;