Advanced servers support clean shutdown via SIGINT or SIGTERM

fix #1026

example/advanced/server-flex/advanced_server_flex.cpp

@@ -23,6 +23,7 @@
 #include <boost/beast/version.hpp>
 #include <boost/asio/bind_executor.hpp>
 #include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/signal_set.hpp>
 #include <boost/asio/ssl/stream.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/asio/steady_timer.hpp>
@@ -1272,6 +1273,17 @@ int main(int argc, char* argv[])
         tcp::endpoint{address, port},
         doc_root)->run();
 
+    // Capture SIGINT and SIGTERM to perform a clean shutdown
+    boost::asio::signal_set signals(ioc, SIGINT, SIGTERM);
+    signals.async_wait(
+        [&](boost::system::error_code const&, int)
+        {
+            // Stop the `io_context`. This will cause `run()`
+            // to return immediately, eventually destroying the
+            // `io_context` and all of the sockets in it.
+            ioc.stop();
+        });
+
     // Run the I/O service on the requested number of threads
     std::vector<std::thread> v;
     v.reserve(threads - 1);
@@ -1283,5 +1295,11 @@ int main(int argc, char* argv[])
         });
     ioc.run();
 
+    // (If we get here, it means we got a SIGINT or SIGTERM)
+
+    // Block until all the threads exit
+    for(auto& t : v)
+        t.join();
+
     return EXIT_SUCCESS;
 }