Simplify thread attach/detach. Use connection specific mysys_var, rather than...

Simplify thread attach/detach. Use connection specific mysys_var, rather than sharing worker thread's my_thread_var with THD.

sql/threadpool_common.cc

@@ -26,99 +26,105 @@ uint threadpool_max_threads;
 uint threadpool_oversubscribe;
 
 
+extern "C" pthread_key(struct st_my_thread_var*, THR_KEY_mysys);
+
 /*
-  Attach/associate the connection with the OS thread, for command processing.
+  Worker threads contexts, and THD contexts.
+  =====================================
+  
+  Both worker threads and connections have their sets of thread local variables 
+  At the moment it is mysys_var (which has e.g dbug my_error and similar 
+  goodies inside), and PSI per-client structure.
+
+  Whenever query is executed following needs to be done:
+
+  1. Save worker thread context.
+  2. Change TLS variables to connection specific ones using thread_attach(THD*).
+     This function does some additional work , e.g setting up 
+     thread_stack/thread_ends_here pointers.
+  3. Process query
+  4. Restore worker thread context.
+
+  Connection login and termination follows similar schema w.r.t saving and 
+  restoring contexts. 
+
+  For both worker thread, and for the connection, mysys variables are created 
+  using my_thread_init() and freed with my_thread_end().
+
 */
-static inline bool thread_attach(THD* thd, char *stack_start, PSI_thread **save_psi_thread)
+struct Worker_thread_context
 {
-  DBUG_ENTER("thread_attach");
+  PSI_thread *psi_thread;
+  st_my_thread_var* mysys_var;
 
-  if (PSI_server)
+  void save()
   {
-    *save_psi_thread= PSI_server->get_thread();
-    PSI_server->set_thread(thd->event_scheduler.m_psi);
+    psi_thread=  PSI_server?PSI_server->get_thread():0;
+    mysys_var= (st_my_thread_var *)pthread_getspecific(THR_KEY_mysys);
   }
-  else
-    *save_psi_thread= NULL;
-   
-  /*
-    We need to know the start of the stack so that we could check for
-    stack overruns.
-  */
-  thd->thread_stack= stack_start;
-
 
-  /* Calls close_connection() on failure */
-  if (setup_connection_thread_globals(thd))
+  void restore()
   {
-    DBUG_RETURN(TRUE);
+    if (PSI_server)
+      PSI_server->set_thread(psi_thread);
+    pthread_setspecific(THR_KEY_mysys,mysys_var);
+    pthread_setspecific(THR_THD, 0);
+    pthread_setspecific(THR_MALLOC, 0);
   }
+};
 
-  /* clear errors from processing the previous THD */
-  my_errno= 0;
-  thd->mysys_var->abort= 0;
-
-#ifndef DBUG_OFF
-  if (thd->event_scheduler.set_explain)
-    DBUG_SET(thd->event_scheduler.dbug_explain);
-#endif
-
-  DBUG_RETURN(FALSE);
-}
 
 /*
-  Detach/disassociate the connection with the OS thread.
+  Attach/associate the connection with the OS thread,
 */
-static inline void thread_detach(THD* thd, PSI_thread *restore_psi_thread)
+static inline bool thread_attach(THD* thd)
 {
-  DBUG_ENTER("thread_detach");
-  mysql_mutex_lock(&thd->LOCK_thd_data);
-  thd->mysys_var = NULL;
-  mysql_mutex_unlock(&thd->LOCK_thd_data);
-#ifndef DBUG_OFF
-  /*
-    If during the session @@session.dbug was assigned, the
-    dbug options/state has been pushed. Check if this is the
-    case, to be able to restore the state when we attach this
-    logical connection to a physical thread.
-  */
-  if (_db_is_pushed_())
-  {
-    thd->event_scheduler.set_explain= TRUE;
-    if (DBUG_EXPLAIN(thd->event_scheduler.dbug_explain, sizeof(thd->event_scheduler.dbug_explain)))
-      sql_print_error("thd_scheduler: DBUG_EXPLAIN buffer is too small");
-  }
-  /* DBUG_POP() is a no-op in case there is no session state */
-  DBUG_POP();
-#endif
+  pthread_setspecific(THR_KEY_mysys,thd->mysys_var);
+  thd->thread_stack=(char*)&thd;
+  thd->store_globals();
   if (PSI_server)
-    PSI_server->set_thread(restore_psi_thread);
-  pthread_setspecific(THR_THD, NULL);
-  DBUG_VOID_RETURN;
+    PSI_server->set_thread(thd->event_scheduler.m_psi);
+  return 0;
 }
 
 
-
 int threadpool_add_connection(THD *thd)
 {
   int retval=1;
-  PSI_thread *psi_thread;
-#ifndef DBUG_OFF
-  thd->event_scheduler.set_explain = 0;
-#endif
-  thread_attach(thd, (char *)&thd, &psi_thread);
-  ulonglong now= microsecond_interval_timer();
-  thd->prior_thr_create_utime= now;
-  thd->start_utime= now;
-  thd->thr_create_utime= now;
+  Worker_thread_context worker_context;
+  worker_context.save();
+
+  /*
+    Create a new connection context: mysys_thread_var and PSI thread 
+    Store them in thd->mysys_var and thd->scheduler.m_psi.
+  */
+
+  /* Use my_thread_init() to create new mysys_thread_var. */
+  pthread_setspecific(THR_KEY_mysys, 0);
+  my_thread_init();
+  thd->mysys_var= (st_my_thread_var *)pthread_getspecific(THR_KEY_mysys);
+  if (!thd->mysys_var)
+  {
+    /* Out of memory? */
+    worker_context.restore();
+    return 1;
+  }
 
+  /* Create new PSI thread for use with the THD. */
   if (PSI_server)
   {
     thd->event_scheduler.m_psi = 
       PSI_server->new_thread(key_thread_one_connection, thd, thd->thread_id);
-    PSI_server->set_thread(thd->event_scheduler.m_psi);
   }
-  
+
+
+  /* Login. */
+  thread_attach(thd);
+  ulonglong now= microsecond_interval_timer();
+  thd->prior_thr_create_utime= now;
+  thd->start_utime= now;
+  thd->thr_create_utime= now;
+
   if (setup_connection_thread_globals(thd) == 0)
   {
     if (login_connection(thd) == 0)
@@ -129,15 +135,19 @@ int threadpool_add_connection(THD *thd)
     }
   }
   thd->skip_wait_timeout= true;
-  thread_detach(thd, psi_thread);
+
+  worker_context.restore();
   return retval;
 }
 
 void threadpool_remove_connection(THD *thd)
 {
-  PSI_thread *save_psi_thread;
 
-  thread_attach(thd, (char *)&thd, &save_psi_thread);
+  Worker_thread_context worker_context;
+  worker_context.save();
+
+  thread_attach(thd);
+
   thd->killed= KILL_CONNECTION;
 
   thd->net.reading_or_writing= 0;
@@ -152,17 +162,21 @@ void threadpool_remove_connection(THD *thd)
   unlink_thd(thd);
   mysql_mutex_unlock(&LOCK_thread_count);
   mysql_cond_broadcast(&COND_thread_count);
-  DBUG_POP();
-  if (PSI_server)
-    PSI_server->delete_current_thread();
-  pthread_setspecific(THR_THD, NULL);
+
+  /* Free resources (thread_var and PSI connection specific struct)*/
+  my_thread_end();
+
+  worker_context.restore();
+
 }
 
 int threadpool_process_request(THD *thd)
 {
   int retval= 0;
-  PSI_thread *psi_thread;
-  thread_attach(thd, (char *)&thd, &psi_thread);
+  Worker_thread_context  worker_context;
+  worker_context.save();
+
+  thread_attach(thd);
 
   if (thd->killed >= KILL_CONNECTION)
   {
@@ -170,7 +184,7 @@ int threadpool_process_request(THD *thd)
       kill flag can be set have been killed by 
       timeout handler or by a KILL command
     */
-    thread_detach(thd, psi_thread);
+    worker_context.restore();
     return 1;
   }
 
@@ -199,9 +213,10 @@ int threadpool_process_request(THD *thd)
       break;
     }
   }
-  thread_detach(thd, psi_thread);
   if (!retval)
     thd->net.reading_or_writing= 1;
+
+  worker_context.restore();
   return retval;
 }