examples: don't exit too early (#2478)

Otherwise, we'd have to use attach.

examples/start_stop_server/start_stop_server.cpp

@@ -4,18 +4,20 @@
 
 #include <mavsdk/mavsdk.h>
 #include <mavsdk/mavsdk_server/mavsdk_server_api.h>
+#include <atomic>
 #include <iostream>
+#include <chrono>
 #include <csignal>
+#include <thread>
 
 using namespace mavsdk;
 
-static struct MavsdkServer* mavsdk_server;
+static std::atomic<bool> _should_stop{false};
 
 void signal_handler(int sig)
 {
     std::cout << "Received signal " << sig << std::endl;
-
-    mavsdk_server_stop(mavsdk_server);
+    _should_stop.store(true);
 }
 
 int main(int argc, char* argv[])
@@ -27,9 +29,18 @@ int main(int argc, char* argv[])
 
     signal(SIGINT, signal_handler);
 
+    MavsdkServer* mavsdk_server;
+
     mavsdk_server_init(&mavsdk_server);
+
+    // This returns when a system has been discovered.
     mavsdk_server_run(mavsdk_server, argv[1], 50051);
 
+    while (!_should_stop.load()) {
+        std::this_thread::sleep_for(std::chrono::seconds(1));
+    }
+
+    mavsdk_server_stop(mavsdk_server);
     mavsdk_server_destroy(mavsdk_server);
 
     return 0;