feat: add average rtt statistics counter

include/neuron/adapter.h

@@ -30,6 +30,8 @@ extern "C" {
 #include "tag.h"
 #include "type.h"
 
+#define NEU_NODE_STAT_RTT_MAX 9999
+
 /** Kinds of node statistics counters.
  *
  * Some counters are maintained by the neuron core, while others should be
@@ -41,6 +43,7 @@ typedef enum {
     NEU_NODE_STAT_BYTES_RECV, // number of bytes received
     NEU_NODE_STAT_MSGS_SENT,  // number of messages sent
     NEU_NODE_STAT_MSGS_RECV,  // number of messages received
+    NEU_NODE_STAT_AVG_RTT,    // average round trip time (ms)
 
     // kinds of counters maintained by the driver core
     NEU_NODE_STAT_TAG_TOT_CNT, // number of tag read including errors
@@ -56,6 +59,7 @@ static inline const char *neu_node_stat_string(neu_node_stat_e s)
         [NEU_NODE_STAT_BYTES_RECV]  = "bytes_received",
         [NEU_NODE_STAT_MSGS_SENT]   = "messages_sent",
         [NEU_NODE_STAT_MSGS_RECV]   = "messages_received",
+        [NEU_NODE_STAT_AVG_RTT]     = "average_rtt",
         [NEU_NODE_STAT_TAG_TOT_CNT] = "tag_total_count",
         [NEU_NODE_STAT_TAG_ERR_CNT] = "tag_error_count",
         [NEU_NODE_STAT_MAX]         = NULL,

src/adapter/adapter.c

@@ -88,6 +88,8 @@ neu_adapter_t *neu_adapter_create(neu_adapter_info_t *info)
     adapter->persister        = neu_persister_create("persistence");
     assert(adapter->persister != NULL);
 
+    adapter->stat.avg_rtt = NEU_NODE_STAT_RTT_MAX;
+
     rv = nng_pair1_open(&adapter->sock);
     assert(rv == 0);
     nng_socket_set_int(adapter->sock, NNG_OPT_RECVBUF, 128);
@@ -184,6 +186,18 @@ static void adapter_stat_acc(neu_adapter_t *adapter, neu_node_stat_e s,
     case NEU_NODE_STAT_MSGS_RECV:
         adapter->stat.msgs_recv += n;
         break;
+    case NEU_NODE_STAT_AVG_RTT: {
+        if (NEU_NODE_STAT_RTT_MAX <= n ||
+            adapter->stat.avg_rtt == NEU_NODE_STAT_RTT_MAX) {
+            adapter->stat.avg_rtt = n;
+            break;
+        }
+
+        // exponential moving average with alpha = 0.3
+        const double a        = 0.3;
+        adapter->stat.avg_rtt = adapter->stat.avg_rtt * (1 - a) + n * a;
+        break;
+    }
 
     // these are maintained by neuron core
     case NEU_NODE_STAT_TAG_TOT_CNT:

src/adapter/adapter_internal.h

@@ -60,6 +60,7 @@ struct neu_adapter {
             uint64_t bytes_recv;  // number of bytes received over network
             uint64_t msgs_sent;   // number of messages sent
             uint64_t msgs_recv;   // number of messages received
+            uint64_t avg_rtt;     // average round trip time in milliseconds
             uint64_t tag_tot_cnt; // number of tag read including errors
             uint64_t tag_err_cnt; // number of tag read errors
         };