1 files changed, 85 insertions, 6 deletions
diff --git a/sql/table.h b/sql/table.h
index 940f135bcf1..2bad6cbf32f 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -581,15 +581,94 @@ enum open_frm_error {
   from persistent statistical tables
 */
 
-struct TABLE_STATISTICS_CB
+class TABLE_STATISTICS_CB
 {
+  class Statistics_state
+  {
+    enum state_codes
+    {
+      EMPTY,   /** data is not loaded */
+      LOADING, /** data is being loaded in some connection */
+      READY    /** data is loaded and available for use */
+    };
+    int32 state;
+
+  public:
+    /** No state copy */
+    Statistics_state &operator=(const Statistics_state &) { return *this; }
+
+    /** Checks if data loading have been completed */
+    bool is_ready() const
+    {
+      return my_atomic_load32_explicit(const_cast<int32*>(&state),
+                                       MY_MEMORY_ORDER_ACQUIRE) == READY;
+    }
+
+    /**
+      Sets mutual exclusion for data loading
+
+      If stats are in LOADING state, waits until state change.
+
+      @return
+        @retval true atomic EMPTY -> LOADING transfer completed, ok to load
+        @retval false stats are in READY state, no need to load
+    */
+    bool start_load()
+    {
+      for (;;)
+      {
+        int32 expected= EMPTY;
+        if (my_atomic_cas32_weak_explicit(&state, &expected, LOADING,
+                                          MY_MEMORY_ORDER_RELAXED,
+                                          MY_MEMORY_ORDER_RELAXED))
+          return true;
+        if (expected == READY)
+          return false;
+        (void) LF_BACKOFF();
+      }
+    }
+
+    /** Marks data available for subsequent use */
+    void end_load()
+    {
+      DBUG_ASSERT(my_atomic_load32_explicit(&state, MY_MEMORY_ORDER_RELAXED) ==
+                  LOADING);
+      my_atomic_store32_explicit(&state, READY, MY_MEMORY_ORDER_RELEASE);
+    }
+
+    /** Restores empty state on error (e.g. OOM) */
+    void abort_load()
+    {
+      DBUG_ASSERT(my_atomic_load32_explicit(&state, MY_MEMORY_ORDER_RELAXED) ==
+                  LOADING);
+      my_atomic_store32_explicit(&state, EMPTY, MY_MEMORY_ORDER_RELAXED);
+    }
+  };
+
+  class Statistics_state stats_state;
+  class Statistics_state hist_state;
+
+public:
   MEM_ROOT  mem_root; /* MEM_ROOT to allocate statistical data for the table */
   Table_statistics *table_stats; /* Structure to access the statistical data */
-  bool stats_can_be_read;        /* Memory for statistical data is allocated */
-  bool stats_is_read;            /* Statistical data for table has been read
-                                    from statistical tables */
-  bool histograms_can_be_read;
-  bool histograms_are_read;   
+  ulong total_hist_size;         /* Total size of all histograms */
+
+  bool histograms_are_ready() const
+  {
+    return !total_hist_size || hist_state.is_ready();
+  }
+
+  bool start_histograms_load()
+  {
+    return total_hist_size && hist_state.start_load();
+  }
+
+  void end_histograms_load() { hist_state.end_load(); }
+  void abort_histograms_load() { hist_state.abort_load(); }
+  bool stats_are_ready() const { return stats_state.is_ready(); }
+  bool start_stats_load() { return stats_state.start_load(); }
+  void end_stats_load() { stats_state.end_load(); }
+  void abort_stats_load() { stats_state.abort_load(); }
 };
 
 /**