MDEV-20372 thread_pool_info fails randomly in 10.5

Rework stats a bit, so we're not missing any queue_get() now.

Don't do stats_reset_table(), if generic threadpool is off.

sql/thread_pool_info.cc

@@ -194,10 +194,10 @@ static int stats_fill_table(THD* thd, TABLE_LIST* tables, COND*)
     table->field[4]->store(counters->wakes_due_to_stall, true);
     table->field[5]->store(counters->throttles, true);
     table->field[6]->store(counters->stalls, true);
-    table->field[7]->store(counters->polls_by_listener, true);
-    table->field[8]->store(counters->polls_by_worker, true);
-    table->field[9]->store(counters->dequeues_by_listener, true);
-    table->field[10]->store(counters->dequeues_by_worker, true);
+    table->field[7]->store(counters->polls[(int)operation_origin::LISTENER], true);
+    table->field[8]->store(counters->polls[(int)operation_origin::WORKER], true);
+    table->field[9]->store(counters->dequeues[(int)operation_origin::LISTENER], true);
+    table->field[10]->store(counters->dequeues[(int)operation_origin::WORKER], true);
     mysql_mutex_unlock(&group->mutex);
     if (schema_table_store_record(thd, table))
       return 1;
@@ -207,6 +207,9 @@ static int stats_fill_table(THD* thd, TABLE_LIST* tables, COND*)
 
 static int stats_reset_table()
 {
+  if (!all_groups)
+    return 0;
+
   for (uint i = 0; i < threadpool_max_size && all_groups[i].pollfd != INVALID_HANDLE_VALUE; i++)
   {
     thread_group_t* group = &all_groups[i];

sql/threadpool_generic.cc

@@ -45,7 +45,6 @@ static void io_poll_close(TP_file_handle fd)
 #endif
 }
 
-
 /** Maximum number of native events a listener can read in one go */
 #define MAX_EVENTS 1024
 
@@ -435,6 +434,16 @@ static TP_connection_generic *queue_get(thread_group_t *thread_group)
   DBUG_RETURN(0);  
 }
 
+static TP_connection_generic* queue_get(thread_group_t* group, operation_origin origin)
+{
+  auto ret = queue_get(group);
+  if (ret)
+  {
+    TP_INCREMENT_GROUP_COUNTER(group, dequeues[(int)origin]);
+  }
+  return ret;
+}
+
 static bool is_queue_empty(thread_group_t *thread_group)
 {
   for (int i=0; i < NQUEUES; i++)
@@ -684,7 +693,7 @@ static TP_connection_generic * listener(worker_thread_t *current_thread,
       break;
   
     cnt = io_poll_wait(thread_group->pollfd, ev, MAX_EVENTS, -1);
-    TP_INCREMENT_GROUP_COUNTER(thread_group, polls_by_listener);
+    TP_INCREMENT_GROUP_COUNTER(thread_group, polls[(int)operation_origin::LISTENER]);
     if (cnt <=0)
     {
       DBUG_ASSERT(thread_group->shutdown);
@@ -750,7 +759,7 @@ static TP_connection_generic * listener(worker_thread_t *current_thread,
     if (listener_picks_event)
     {
       /* Handle the first event. */
-      retval= queue_get(thread_group);
+      retval= queue_get(thread_group, operation_origin::LISTENER);
       mysql_mutex_unlock(&thread_group->mutex);
       break;
     }
@@ -1130,10 +1139,9 @@ TP_connection_generic *get_event(worker_thread_t *current_thread,
     /* Check if queue is not empty */
     if (!oversubscribed)
     {
-      connection = queue_get(thread_group);
+      connection = queue_get(thread_group, operation_origin::WORKER);
       if(connection)
       {
-        TP_INCREMENT_GROUP_COUNTER(thread_group,dequeues_by_worker);
         break;
       }
     }
@@ -1146,10 +1154,7 @@ TP_connection_generic *get_event(worker_thread_t *current_thread,
       mysql_mutex_unlock(&thread_group->mutex);
 
       connection = listener(current_thread, thread_group);
-      if (connection)
-      {
-        TP_INCREMENT_GROUP_COUNTER(thread_group, dequeues_by_listener);
-      }
+
       mysql_mutex_lock(&thread_group->mutex);
       thread_group->active_thread_count++;
       /* There is no listener anymore, it just returned. */
@@ -1167,11 +1172,11 @@ TP_connection_generic *get_event(worker_thread_t *current_thread,
     {
       native_event ev[MAX_EVENTS];
       int cnt = io_poll_wait(thread_group->pollfd, ev, MAX_EVENTS, 0);
-      TP_INCREMENT_GROUP_COUNTER(thread_group, polls_by_worker);
+      TP_INCREMENT_GROUP_COUNTER(thread_group, polls[(int)operation_origin::WORKER]);
       if (cnt > 0)
       {
         queue_put(thread_group, ev, cnt);
-        connection= queue_get(thread_group);
+        connection= queue_get(thread_group,operation_origin::WORKER);
         break;
       }
     }

sql/threadpool_generic.h

@@ -108,6 +108,12 @@ typedef I_P_List<TP_connection_generic,
 
 const int NQUEUES = 2; /* We have high and low priority queues*/
 
+enum class operation_origin
+{
+  WORKER,
+  LISTENER
+};
+
 struct thread_group_counters_t
 {
   ulonglong thread_creations;
@@ -116,10 +122,8 @@ struct thread_group_counters_t
   ulonglong wakes_due_to_stall;
   ulonglong throttles;
   ulonglong stalls;
-  ulonglong dequeues_by_worker;
-  ulonglong dequeues_by_listener;
-  ulonglong polls_by_listener;
-  ulonglong polls_by_worker;
+  ulonglong dequeues[2];
+  ulonglong polls[2];
 };
 
 struct MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE) thread_group_t
@@ -143,7 +147,7 @@ struct MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE) thread_group_t
   thread_group_counters_t counters;
 };
 
-#define TP_INCREMENT_GROUP_COUNTER(group,var) group->counters.var++;
+#define TP_INCREMENT_GROUP_COUNTER(group,var) do {group->counters.var++;}while(0)
 
 extern thread_group_t* all_groups;
 #endif