tc_active_instances: my_atomic to std::atomic

Author: svoj

sql/mysqld.cc

@@ -7831,7 +7831,7 @@ SHOW_VAR status_vars[]= {
  {"Subquery_cache_miss", (char*) &subquery_cache_miss, SHOW_LONG},
  {"Table_locks_immediate", (char*) &locks_immediate, SHOW_LONG},
  {"Table_locks_waited", (char*) &locks_waited, SHOW_LONG},
- {"Table_open_cache_active_instances", (char*) &tc_active_instances, SHOW_UINT},
+ {"Table_open_cache_active_instances", (char*) &show_tc_active_instances, SHOW_SIMPLE_FUNC},
  {"Table_open_cache_hits", (char*) offsetof(STATUS_VAR, table_open_cache_hits), SHOW_LONGLONG_STATUS},
  {"Table_open_cache_misses", (char*) offsetof(STATUS_VAR, table_open_cache_misses), SHOW_LONGLONG_STATUS},
  {"Table_open_cache_overflows", (char*) offsetof(STATUS_VAR, table_open_cache_overflows), SHOW_LONGLONG_STATUS},

sql/table_cache.cc

@@ -56,7 +56,7 @@
 ulong tdc_size; /**< Table definition cache threshold for LRU eviction. */
 ulong tc_size; /**< Table cache threshold for LRU eviction. */
 uint32 tc_instances;
-uint32 tc_active_instances= 1;
+static std::atomic<uint32_t> tc_active_instances(1);
 static std::atomic<bool> tc_contention_warning_reported;
 
 /** Data collections. */
@@ -163,7 +163,7 @@ struct Table_cache_instance
  overhead on TABLE object release. All other table cache mutex acquistions
  are considered out of hot path and are not instrumented either.
  */
- void lock_and_check_contention(uint32 n_instances, uint32 instance)
+ void lock_and_check_contention(uint32_t n_instances, uint32_t instance)
  {
  if (mysql_mutex_trylock(&LOCK_table_cache))
  {
@@ -172,11 +172,10 @@ struct Table_cache_instance
  {
  if (n_instances < tc_instances)
  {
- if (my_atomic_cas32_weak_explicit((int32*) &tc_active_instances,
- (int32*) &n_instances,
- (int32) n_instances + 1,
- MY_MEMORY_ORDER_RELAXED,
- MY_MEMORY_ORDER_RELAXED))
+ if (tc_active_instances.
+ compare_exchange_weak(n_instances, n_instances + 1,
+ std::memory_order_relaxed,
+ std::memory_order_relaxed))
  {
  sql_print_information("Detected table cache mutex contention at instance %d: "
  "%d%% waits. Additional table cache instance "
@@ -354,8 +353,8 @@ void tc_purge(bool mark_flushed)
 
 void tc_add_table(THD *thd, TABLE *table)
 {
- uint32 i= thd->thread_id % my_atomic_load32_explicit((int32*) &tc_active_instances,
-  MY_MEMORY_ORDER_RELAXED);
+ uint32_t i=
+ thd->thread_id % tc_active_instances.load(std::memory_order_relaxed);
  TABLE *LRU_table= 0;
  TDC_element *element= table->s->tdc;
 
@@ -408,10 +407,8 @@ void tc_add_table(THD *thd, TABLE *table)
 
 TABLE *tc_acquire_table(THD *thd, TDC_element *element)
 {
- uint32 n_instances=
- my_atomic_load32_explicit((int32*) &tc_active_instances,
- MY_MEMORY_ORDER_RELAXED);
- uint32 i= thd->thread_id % n_instances;
+ uint32_t n_instances= tc_active_instances.load(std::memory_order_relaxed);
+ uint32_t i= thd->thread_id % n_instances;
  TABLE *table;
 
  tc[i].lock_and_check_contention(n_instances, i);
@@ -1342,3 +1339,14 @@ int tdc_iterate(THD *thd, my_hash_walk_action action, void *argument,
  }
  return res;
 }
+
+
+int show_tc_active_instances(THD *thd, SHOW_VAR *var, char *buff,
+ enum enum_var_type scope)
+{
+ var->type= SHOW_UINT;
+ var->value= buff;
+ *(reinterpret_cast<uint32_t*>(buff))=
+ tc_active_instances.load(std::memory_order_relaxed);
+ return 0;
+}

sql/table_cache.h

@@ -71,7 +71,6 @@ enum enum_tdc_remove_table_type
 extern ulong tdc_size;
 extern ulong tc_size;
 extern uint32 tc_instances;
-extern uint32 tc_active_instances;
 
 extern bool tdc_init(void);
 extern void tdc_start_shutdown(void);
@@ -98,6 +97,8 @@ extern int tdc_iterate(THD *thd, my_hash_walk_action action, void *argument,
  bool no_dups= false);
 
 extern uint tc_records(void);
+int show_tc_active_instances(THD *thd, SHOW_VAR *var, char *buff,
+ enum enum_var_type scope);
 extern void tc_purge(bool mark_flushed= false);
 extern void tc_add_table(THD *thd, TABLE *table);
 extern void tc_release_table(TABLE *table);