MXS-1992 Expose qc stats in threads info

In principle it would be better if the qc information were
obtained via a specific query_classifier resource. However,
there are multiple problems with that (e.g. the qc has no way
of safely accessing information of another thread) and hence
the worker specific qc cache statistics is reported as part of
the worker statistics.

include/maxscale/query_classifier.h

@@ -14,6 +14,7 @@
 
 #include <maxscale/cdefs.h>
 #include <maxscale/buffer.h>
+#include <maxscale/jansson.h>
 
 MXS_BEGIN_DECLS
 
@@ -871,4 +872,11 @@ uint64_t qc_get_server_version();
  */
 bool qc_get_cache_stats(QC_CACHE_STATS* stats);
 
+/**
+ * Get cache statistics for the calling thread.
+ *
+ * @return An object if caching is enabled, NULL otherwise.
+ */
+json_t* qc_get_cache_stats_as_json();
+
 MXS_END_DECLS

server/core/query_classifier.cc

@@ -1208,3 +1208,26 @@ bool qc_get_cache_stats(QC_CACHE_STATS* pStats)
 
     return rv;
 }
+
+json_t* qc_get_cache_stats_as_json()
+{
+    json_t* pStats;
+
+    QC_CACHE_STATS stats;
+
+    if (qc_get_cache_stats(&stats))
+    {
+        pStats = json_object();
+
+        if (pStats)
+        {
+            json_object_set_new(pStats, "size", json_integer(stats.size));
+            json_object_set_new(pStats, "inserts", json_integer(stats.inserts));
+            json_object_set_new(pStats, "hits", json_integer(stats.hits));
+            json_object_set_new(pStats, "misses", json_integer(stats.misses));
+            json_object_set_new(pStats, "evictions", json_integer(stats.evictions));
+        }
+    }
+
+    return pStats;
+}

server/core/routingworker.cc

@@ -973,7 +973,7 @@ std::unique_ptr<json_t> RoutingWorker::get_qc_stats_as_json(const char* zHost, i
         stringstream self;
         self << MXS_JSON_API_QC_STATS << id;
 
-        sStats = std::unique_ptr<json_t>(mxs_json_resource(zHost, self.str().c_str(), pJson));
+        sStats.reset(mxs_json_resource(zHost, self.str().c_str(), pJson));
     }
 
     return sStats;
@@ -1088,6 +1088,13 @@ public:
         json_object_set_new(load, "last_hour", json_integer(rworker.load(Worker::Load::ONE_HOUR)));
         json_object_set_new(pStats, "load", load);
 
+        json_t* qc = qc_get_cache_stats_as_json();
+
+        if (qc)
+        {
+            json_object_set_new(pStats, "query_classifier_cache", qc);
+        }
+
         json_t* pAttr = json_object();
         json_object_set_new(pAttr, "stats", pStats);