core: deadlock fix, remove empty system, relax version request

src/mavsdk/core/mavsdk_impl.cpp

@@ -372,19 +372,6 @@ void MavsdkImpl::receive_message(mavlink_message_t& message, Connection* connect
 
     std::lock_guard<std::recursive_mutex> lock(_systems_mutex);
 
-    // The only situation where we create a system with sysid 0 is when we initialize the connection
-    // to the remote.
-    if (_systems.size() == 1 && _systems[0].first == 0) {
-        LogDebug() << "New: System ID: " << static_cast<int>(message.sysid)
-                   << " Comp ID: " << static_cast<int>(message.compid);
-        _systems[0].first = message.sysid;
-        _systems[0].second->system_impl()->set_system_id(message.sysid);
-
-        // Even though the fake system was already discovered, we can now
-        // send a notification, now that it seems to really actually exist.
-        notify_on_discover();
-    }
-
     bool found_system = false;
     for (auto& system : _systems) {
         if (system.first == message.sysid) {
@@ -559,12 +546,8 @@ std::pair<ConnectionResult, Mavsdk::ConnectionHandle> MavsdkImpl::setup_udp_remo
         new_conn->add_remote(remote_ip, remote_port);
         auto handle = add_connection(new_conn);
         std::lock_guard<std::recursive_mutex> lock(_systems_mutex);
-        if (_systems.empty()) {
-            make_system_with_component(0, 0);
-        }
 
-        // With a UDP remote, we need to initiate the connection by sending
-        // heartbeats.
+        // With a UDP remote, we need to initiate the connection by sending heartbeats.
         auto new_configuration = get_configuration();
         new_configuration.set_always_send_heartbeats(true);
         set_configuration(new_configuration);

src/mavsdk/core/system_impl.cpp

@@ -504,8 +504,8 @@ void SystemImpl::send_autopilot_version_request()
 
     if (fut.get() == MavlinkCommandSender::Result::Unsupported) {
         _old_message_520_supported = false;
-        LogWarn() << "Trying alternative command (512).";
-        send_autopilot_version_request();
+        LogWarn()
+            << "Trying alternative command REQUEST_MESSAGE instead of REQUEST_AUTOPILOT_CAPABILITIES next.";
     }
 }
 
@@ -541,12 +541,6 @@ void SystemImpl::set_connected()
 
             _connected = true;
 
-            // System with sysid 0 is a bit special: it is a placeholder for a connection initiated
-            // by MAVSDK. As such, it should not be advertised as a newly discovered system.
-            if (static_cast<int>(get_system_id()) != 0) {
-                _mavsdk_impl.notify_on_discover();
-            }
-
             // We call this later to avoid deadlocks on creating the server components.
             _mavsdk_impl.call_user_callback([this]() {
                 // Send a heartbeat back immediately.
@@ -568,6 +562,9 @@ void SystemImpl::set_connected()
         }
         // If not yet connected there is nothing to do/
     }
+
+    _mavsdk_impl.notify_on_discover();
+
     if (enable_needed) {
         if (has_autopilot()) {
             send_autopilot_version_request_async(nullptr);
@@ -591,10 +588,10 @@ void SystemImpl::set_disconnected()
         //_heartbeat_timeout_cookie = nullptr;
 
         _connected = false;
-        _mavsdk_impl.notify_on_timeout();
         _is_connected_callbacks.queue(
             false, [this](const auto& func) { _mavsdk_impl.call_user_callback(func); });
     }
+    _mavsdk_impl.notify_on_timeout();
 
     _mavsdk_impl.stop_sending_heartbeats();
 

src/mavsdk/plugins/info/info_impl.cpp

@@ -52,7 +52,7 @@ void InfoImpl::enable()
 {
     // We're going to retry until we have the version.
     _system_impl->add_call_every(
-        [this]() { _system_impl->send_autopilot_version_request(); }, 1.0f, &_call_every_cookie);
+        [this]() { _system_impl->send_autopilot_version_request(); }, 2.0f, &_call_every_cookie);
 
     if (!_flight_info_subscriptions.empty()) {
         // We're hoping to get flight information regularly to update flight time.