dht_proxy_server: avoid mutex when getting /

The dht_proxy_server should be always up, so getNodesStats will
be pretty always up-to-date. We can add it into a job and avoid
to wait for this method to finish (and this method use an
internal lock) to have a quick answer about the status of the proxy.

Note: the update is forced during the initialization of the proxy

src/dht_proxy_server.cpp

@@ -30,6 +30,8 @@
 #include <functional>
 #include <limits>
 
+#include <iostream>
+
 using namespace std::placeholders;
 
 namespace dht {
@@ -128,6 +130,16 @@ DhtProxyServer::DhtProxyServer(std::shared_ptr<DhtRunner> dht, in_port_t port ,
                 std::cout << getStats().toString() << std::endl;
                 scheduler_.edit(printStatsJob_, scheduler_.time() + PRINT_STATS_PERIOD);
             }
+            if (not stopListeners) {
+                // Refresh stats cache
+                auto newIpv4Stats = dht_->getNodesStats(AF_INET);
+                auto newIpv6Stats = dht_->getNodesStats(AF_INET6);
+                {
+                    std::lock_guard<std::mutex> lck(statsMutex_);
+                    ipv4Stats_ = std::move(newIpv4Stats);
+                    ipv6Stats_ = std::move(newIpv6Stats);
+                }
+            }
         });
         while (service_->is_up()  and not stopListeners) {
             std::unique_lock<std::mutex> lock(schedulerLock_);
@@ -205,8 +217,19 @@ DhtProxyServer::getNodeInfo(const std::shared_ptr<restbed::Session>& session) co
                     if (id)
                         result["id"] = id.toString();
                     result["node_id"] = dht_->getNodeId().toString();
-                    result["ipv4"] = dht_->getNodesStats(AF_INET).toJson();
-                    result["ipv6"] = dht_->getNodesStats(AF_INET6).toJson();
+                    {
+                        std::lock_guard<std::mutex> lck(statsMutex_);
+                        if (ipv4Stats_.good_nodes == 0 && ipv6Stats_.good_nodes == 0) {
+                            // NOTE: we want to avoid the disconnected state as much as possible
+                            // So, if the node is disconnected, we should force the update of the cache
+                            // and reconnect as soon as possible
+                            // This should not happen much
+                            ipv4Stats_ = dht_->getNodesStats(AF_INET);
+                            ipv6Stats_ = dht_->getNodesStats(AF_INET);
+                        }
+                        result["ipv4"] = ipv4Stats_.toJson();
+                        result["ipv6"] = ipv6Stats_.toJson();
+                    }
                     result["public_ip"] = s->get_origin(); // [ipv6:ipv4]:port or ipv4:port
                     Json::StreamWriterBuilder wbuilder;
                     wbuilder["commentStyle"] = "None";