MySQL£º´ó²¢·¢ÏÂTRX_SYS mutex°¸Àý·ÖÎö

for (view = UT_LIST_GET_LAST(m_views);
      view != NULL;
      view = UT_LIST_GET_PREV(m_view_list, view)) {

  if (!view->is_closed()) {
   break;
  }
 }

(gdb) p trx_sys->mvcc->m_views
$12 = {count = 4, start = 0x33deb78, end = 0x33ded58, node = &ReadView::m_view_list, init = 51966}

class MVCC£º
private:
 typedef UT_LIST_BASE_NODE_T(ReadView) view_list_t;

 /** Free views ready for reuse. */
 view_list_t  m_free;

 /** Active and closed views, the closed views will have the
 creator trx id set to TRX_ID_MAX */
 view_list_t  m_views;

class ReadView£º
   class ids_t:
      /** Memory for the array */
    value_type* m_ptr;

    /** Number of active elements in the array */
    ulint  m_size;

    /** Size of m_ptr in elements */
    ulint  m_reserved;

 trx_id_t m_low_limit_id;
 trx_id_t m_up_limit_id;
 trx_id_t m_creator_trx_id;
 ids_t  m_ids; //µ±Ç°rw trx_id vectorÊý×é
 /** The view does not need to see the undo logs for transactions
 whose transaction number is strictly smaller (<) than this value:
 they can be removed in purge if not needed by other views */
 trx_id_t m_low_limit_no;
 bool  m_closed; //ÊÇ·ñ¹Ø±Õ
 /** This is a view cloned by clone but not by
 MVCC::clone_oldest_view. Used to make sure the cloned transaction does
 not see its own changes. */
 bool  m_cloned;

 typedef UT_LIST_NODE_T(ReadView) node_t;
 byte  pad1[64 - sizeof(node_t)];
 node_t  m_view_list;   //ÔÚtrx_sysÉϵÄÁ´±ínode
 

MVCC  ---> m_free
      ---> m_views


trx_sys->mvcc->m_views


1¡¢½¨Á¢
    
MVCC::view_open
  ->if (view != NULL)
    Èç¹ûÊÓͼ´æÔÚ
  ->uintptr_t p = reinterpret_cast<uintptr_t>(view); 
    view = reinterpret_cast<ReadView*>(p & ~1); 
    ת»»Ö¸Õë
  ->ut_ad(view->m_closed); 
    ¶ÏÑÔm_closedΪfalse
  ->if (trx_is_autocommit_non_locking(trx) && view->empty())
    Èç¹ûÊÂÎñÊÇautocommitÇÒÎÞËø,²¢ÇÒûÓжÁдÊÂÎñ
    ->view->m_closed = false; 
      ÉèÖÃfalse
    ->if (view->m_low_limit_id == trx_sys_get_max_trx_id())
      Èç¹û ÉÏÏÞµÈÓÚµ±Ç°×î´óµÄmax trx id
      return; 
      Ö±½Ó·µ»Ø
    ->mutex_enter(&trx_sys->mutex)
      ¼ÓËø
    ->UT_LIST_REMOVE(m_views, view); 
      ´Ómvcc m_viewsÖÐÒƳýÕâ¸öview
  ->else
    Èç¹ûÊÓͼΪ¿Õ
    ->mutex_enter(&trx_sys->mutex); 
      ¼ÓËø
    ->view = get_view(MVCC::get_view)
      »ñÈ¡Ò»¸öеÄview
      ->if (UT_LIST_GET_LEN(m_free) > 0)
        Èç¹û´æÔÚ¿ÕÏеÄread view  
        ->view = UT_LIST_GET_FIRST(m_free);
          ´ÓfreeÖзÖÅä
        ->UT_LIST_REMOVE(m_free, view);
          ´Óm_freeÖÐÈ¥µô  
      ->else
        Èç¹ûûÓпÕÏеÄview
        ->view = UT_NEW_NOKEY(ReadView());
         ·ñÔòÐèÒª³õʼ»¯ÁË 
  ->if (view != NULL)
    ÕâÀï¾ÍÄõ½ÁËviewÁË
    ->view->prepare(trx->id);
      ->ReadView::prepare
        È·ÈϼÓËø
        ->m_creator_trx_id = id
          ¼Ç¼½¨Á¢Õâ¸öviewµÄtrx_id
        ->m_low_limit_no = m_low_limit_id = trx_sys->max_trx_id;
          ÉèÖÃΪµ±Ç°×î´óµÄtrx id
        ->if (!trx_sys->rw_trx_ids.empty())
          Èç¹ûµ±Ç°rw trxid Êý×鲻Ϊ¿Õ
          ->copy_trx_ids(trx_sys->rw_trx_ids)
            ½«trx_sysµÄrw_trx_ids¶ÁдÊÂÎñÊý×飬¿½±´µ½Õâ¸öviewÖÐ
        ->else
          Èç¹ûµ±Ç°rw trxidΪ¿Õ
          m_ids.clear(); 
        ->if (UT_LIST_GET_LEN(trx_sys->serialisation_list) > 0)
          Èç¹ûÌá½»ÖеÄÊÂÎñ´óÓÚ0 
          ->trx = UT_LIST_GET_FIRST(trx_sys->serialisation_list);
            »ñÈ¡Ìá½»ÊÂÎñÖеÄÒ»¸öÊÂÎñ,Í·²¿
          ->if (trx->no < m_low_limit_no)
            Èç¹ûÕâ¸öÊÂÎñµÄtrx_noСÓÚtrx_sys->max_trx_id
            ->m_low_limit_no = trx->no       
    ->MVCC::complete(view->complete())
      ->m_up_limit_id = !m_ids.empty() ? m_ids.front() : m_low_limit_id;
        Èç¹ûm_idsÓлîÔ¾RWÊÂÎñ£¬¾ÍÉèÖÃm_up_limit_idΪm_ids vectorµÄµÚÒ»¸ö(×îСµÄÒ»¸ö)
      ->m_closed = false;
        ÉèÖÃΪfalse        
    ->MVCC::view_add(view_add(view))
      ->ut_ad(trx_sys_mutex_own())
        »¹ÊÇÏȶÏÑÔ¼ÓËø
      ->UT_LIST_ADD_FIRST(m_views, const_cast<ReadView *>(view))
        ¼ÓÈëµ½MVCCµÄm_viewsÁ´±íÖÐ
  ->trx_sys_mutex_exit();
    ½âËø
    
    
2¡¢¹Ø±Õ


MVCC::view_close ¶ÔÓÚauto commitµÄselectµÚ¶þ¸ö²ÎÊýΪfalse
  ->p = reinterpret_cast<uintptr_t>(view)
  ->if (!own_mutex) 
    ´Óopen viewÀ´¿´Èç¹ûÊÇauto commitÇÒÊÇÖ»¶ÁÊý¾Ý£¬²¢ÇÒÈç¹ûûÓÐrwÊÂÎñ
    ÕâÕâÀï¿ÉÒÔÊÇown_mutex=false
    ->ReadView* ptr = reinterpret_cast<ReadView*>(p & ~1);
      »ñÈ¡Õâ¸öÖ¸Õë
      ptr->m_closed = true;
    ptr->m_cloned = false;
    /* Set the view as closed. */
    view = reinterpret_cast<ReadView*>(p | 0x1);
    Õû¸ö¹ý³Ì²»Éæ¼°µ½MVCCµÄÐ޸ģ¬Ö»ÊÇͨ¹ý±¾ÊÓͼ½øÐÐÐ޸ģ¬±ê¼ÇΪclose
  ->else
    view = reinterpret_cast<ReadView*>(p & ~1);
    view->close();
    UT_LIST_REMOVE(m_views, view);
    ´ÓMVCC Á´±íÖÐÈ¥µô
  UT_LIST_ADD_LAST(m_free, view);
    ¼ÓÈëµ½freeÖÐ
    view = NULL;
    ÇåÀíviewÖ¸Õë
    
    
trx_disconnect_from_mysql
  ...
  if (trx->read_view != NULL) {
  trx_sys->mvcc->view_close(trx->read_view, true);
 }
 ...