feat: Graceful shutdown (#1801)

Fixes #442.

src/web/ng/impl/ConnectionHandler.hpp

@@ -19,8 +19,12 @@
 
 #pragma once
 
+#include "util/StopHelper.hpp"
 #include "util/Taggable.hpp"
 #include "util/log/Logger.hpp"
+#include "util/prometheus/Gauge.hpp"
+#include "util/prometheus/Label.hpp"
+#include "util/prometheus/Prometheus.hpp"
 #include "web/SubscriptionContextInterface.hpp"
 #include "web/ng/Connection.hpp"
 #include "web/ng/Error.hpp"
@@ -33,8 +37,11 @@
 #include <boost/signals2/signal.hpp>
 #include <boost/signals2/variadic_signal.hpp>
 
+#include <atomic>
+#include <chrono>
 #include <cstddef>
 #include <functional>
+#include <memory>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -77,6 +84,12 @@ private:
     std::optional<MessageHandler> wsHandler_;
 
     boost::signals2::signal<void()> onStop_;
+    std::unique_ptr<std::atomic_bool> stopping_ = std::make_unique<std::atomic_bool>(false);
+
+    std::reference_wrapper<util::prometheus::GaugeInt> connectionsCounter_ =
+        PrometheusService::gaugeInt("connections_total_number", util::prometheus::Labels{{{"status", "connected"}}});
+
+    util::StopHelper stopHelper_;
 
 public:
     ConnectionHandler(
@@ -87,6 +100,8 @@ public:
         OnDisconnectHook onDisconnectHook
     );
 
+    static constexpr std::chrono::milliseconds kCLOSE_CONNECTION_TIMEOUT{500};
+
     void
     onGet(std::string const& target, MessageHandler handler);
 
@@ -99,8 +114,14 @@ public:
     void
     processConnection(ConnectionPtr connection, boost::asio::yield_context yield);
 
+    static void
+    stopConnection(Connection& connection, boost::asio::yield_context yield);
+
     void
-    stop();
+    stop(boost::asio::yield_context yield);
+
+    bool
+    isStopping() const;
 
 private:
     /**