feat: Graceful shutdown (#1801)

Fixes #442.

src/util/StopHelper.cpp

@@ -0,0 +1,46 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "util/StopHelper.hpp"
+
+#include <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
+
+#include <chrono>
+
+namespace util {
+
+void
+StopHelper::readyToStop()
+{
+    onStopReady_();
+    *stopped_ = true;
+}
+
+void
+StopHelper::asyncWaitForStop(boost::asio::yield_context yield)
+{
+    boost::asio::steady_timer timer{yield.get_executor(), std::chrono::steady_clock::duration::max()};
+    onStopReady_.connect([&timer]() { timer.cancel(); });
+    boost::system::error_code error;
+    if (!*stopped_)
+        timer.async_wait(yield[error]);
+}
+
+}  // namespace util